research questions about the earthquake

Questions and answers on the subject of earthquakes

Faqs on the subject of earthquakes are answered by researchers from the helmholtz-gemeinschaft (helmholtz association)..

1. What are earthquakes and what causes them? 2. How many earthquakes occur annually worldwide? 3. What equipment is used to record and measure earthquakes? 4. Where do earthquakes occur most frequently? 5. Is it possible to predict earthquakes? 6. Why are the values published on the magnitude of an earthquake sometimes slightly different? 7. Where can I obtain information on current and past earthquakes? 8. How can I protect myself during an earthquake? 9. How much energy is released by an earthquake? 10. How large is the risk of an earthquake in Germany? 11. What was the strongest earthquake ever recorded in Germany? 12. What does epicentre mean? 13. What is the intensity of an earthquake? 14. What is "earthquake magnitude"? 15. What is a Richter scale? 16. What was the strongest earthquake ever recorded? 17. Which magnitude values can be distinguished from each other? 18. Are earthquake-proof building structures possible? 19. Why can the ground liquefy due to an earthquake?

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1. What are earthquakes and what causes them?

Earthquakes are rupturing processes in the Earth's crust that lead to vibrations on the sur­face layer of the planet. Most of the damaging earthquakes so far have been tectonic in origin (tectonic quakes).  They are caused by a sudden displacement along a fracture face in the Earth's crust and by the resulting release of accumulated elastic energy. These fault zones are predominantly located along plate boundaries. However, there are other reasons than tectonics for the occurrence of earthquakes.

2. How many earthquakes occur annually worldwide?

Very strong earthquakes with magnitudes of 8 and higher occur once a year on a global average. On average, 15 quakes ranging in magnitude between 7 and 8 strike on an annual basis. Quakes with magnitudes greater than 7 can have devastating effects on people and the environment. Up to 1,300 moderate quakes on a scale of 5 to 6 take place worldwide every year, smaller quakes with magnitudes of 3 to 4 occur, roughly speaking, 130,000 times a year. Magnitude 3 earthquakes are usually still noticed by people if they are in the vicinity of the epicentre, but in most cases they do not cause any damage.

3. What equipment is used to record and measure earthquakes?

Earthquakes are usually measured by seismometers. Seismometers are installed on the Earth's surface around the globe in particularly "quiet places", generally in seismological observatories. These may be old tunnels, basements in remote buildings or specifically dedicated buildings on their own piece of land. The best-known seismological observatories in Germany are located in the Black Forest (BFO station near Schlitach), in Bavaria (WET station near Wetzell) and in Thuringia (MOX station near Jena). The Deutsches GeoForschungsZentrum (German Research Centre for Geosciences — GFZ) operates seismological stations in cooperation with research institutions in other countries around the world. All observatories record their data on a standardised time basis (Coordinated Universal Time, UTC), so that the data of a recorded earthquake can be collected in one place and jointly analysed.  In addition to the traditional observatories, seismometers are now being operated on the sea floor, at active volcanoes, on ice floes, in glaciers, and even temporarily on the moon.

4. Where do earthquakes occur most frequently?

The uppermost layers of the earth are made up of many rigid plates (tectonic plates) that either slide towards or away from each other or over and under each other. The strongest earthquakes usually occur along the plate boundaries. Severely affected regions include, for example, the west coast of North and South America, Indonesia, Japan, Central Asia and parts of China and Turkey, and in Europe, Italy, Greece and Iceland in particular, where strong quakes are recurrent.

5. Is it possible to predict earthquakes?

No, the precise date, place and magnitude of an earthquake cannot be predicted. However, seismologists nowadays develop seismic hazard maps in which the probability of the occurrence of strong ground tremors due to tectonic quakes can be indicated for a specific period.

6. Why are the values published on the strength of an earthquake sometimes slightly different?

One reason may be that different "strength scales" are being cited. For example, there are several different magnitude scales for earthquakes that are based on different types of data and analyses. Other reasons could be that just after an earthquake has struck, the various services and observatories can initially only access different monitoring stations and are not yet able to share or analyse all the data completely. This may be one of the reasons for slightly different results for one and the same magnitude scale. The first early statements about the strength of an earthquake are associated with greater uncertainties due to the still small amount of data. Over the course of time, more and more data is analysed by an increasing number of monitoring stations, so that the statements about the strength of an earthquake become more accurate.

7. Where can I obtain information on current and past earthquakes?

The GFZ in Potsdam operates a global network of stations consisting of over 100 stations in which seismometers detect ground tremors. All in all, there are only a few of these global networks, but they all work closely together. The denser the monitoring network, the faster the location of the epicentre and the magnitude of the earthquake can be determined. GEOFON stands for GEOFOrschungsNetzwerk (Geosciences Research Network). You can find current global earthquake reports at www.gfz-potsdam.de/portal/gfz/Services .

8. How can I protect myself during an earthquake?

If you are inside a building:

There is no specific protection against earthquakes as they cannot yet be predicted. However, the GFZ has published a list of rules of conduct: Stay calm! Do not panic! Do not jump out of the window or from the balcony! Seek immediate protection beneath a heavy, sturdy piece of furniture (for example a table) and hold on tight to something as long as the tremors persist, even if the furniture moves. If this is not possible, take refuge under a sturdy door frame or lie down on the floor near to a load-bearing interior wall away from windows and protect your head and face with crossed arms. Stay in the building as long as the earthquake tremors persist! The most dangerous thing you can do is to try and leave the building during the quake. You can be injured by falling objects or broken glass. Exception: When the earthquake begins, you are on the ground floor and near to an exit door that leads directly to the outside (garden or open square, not a narrow street). Do not use the stairs! Do not use the elevator!

If you are outdoors:

Go as quickly as possible to an open area, far away from buildings, street lamps and utility lines. Stay there until the tremors have stopped. If you are in a car, drive immediately to the side of the road, away from buildings, trees, flyovers and utility lines. Stay in the car as long as the earthquake tremors persist! Turn on the radio. Do not drive over bridges, cross-roads or below flyovers! When the quake has subsided, continue to drive with the utmost caution (avoid bridges and ramps that could have been damaged by the event) or leave the car parked where it is. If you are at the foot of a steep slope when the tremors begin, move immediately away from it (risk of landslides or falling rocks!). If you feel earth­quake tremors along a flat coastline, run as fast as you can inland to the highest point possi­ble. An earthquake can trigger extreme (up to 30 m high) ocean waves (tsunami). These waves sometimes hit the shoreline long after the quake tremors have subsided. A second wave can also follow a lot later. For this reason, do not leave your elevated place of refuge until the official tsunami all-clear has been given.

9. How much energy is released by an earthquake?

A magnitude 3 earthquake, which people can feel under favourable conditions, releases a seismic energy of approximately two billion joules, which corresponds to 555.6 kilowatt hours (kWh). With every added increment of magnitude, the energy increases by a factor of 30. In 2010, the average energy consumption of a private household was 66 GJ, which corresponds to 18,335 MWh and an earthquake magnitude of 4. A highly destructive magnitude 7 quake releases an energy volume of 450 gigawatt hours, which is ten per cent of the annual electrical energy volume provided by the block of a modern coal-fired power plant. In 2011, the total consumption of all private households in Germany added together came to 2194 PJ (source: Arbeitsgemeinschaft Energiebilanzen [Working Group on Energy Balances] 10/2012), which corresponds roughly to a magnitude 9 earthquake.

10. How large is the risk of earthquakes in Germany?

The risk of earthquakes in Germany is relatively low in global terms, but still not negligible. Smaller quakes occur quite frequently in particular in the area of the Rhine, the Swabian Alb, in eastern Thuringia and western Saxony, including the earthquake swarm area of Vogtland. However, clearly perceptible or even destructive quakes are rare events in Germany.

11. What was the strongest earthquake in Germany so far?

The strongest historically documented quake with an estimated magnitude of roughly 6.1 occurred on 18 February 1756 in the German region of the Lower Rhine Basin in the Cologne-Aachen-Düren area.  One person was killed. If an earthquake of similar magnitude to the one in 1756 occurred today in the same location, the impact would be much more grievous due to the greater population density. In 1750, Cologne, for example, with less than 50,000 inhabitants, had almost one-twentieth of its current population. One of the strongest earthquakes in recent history hit Germany in the early morning hours of 13 April 1992 in the German-Dutch border area. The epicentre was located four kilometres to the southwest of Roermond in the Netherlands. The quake's hypocentre with a magnitude of 5.9 was located at a depth of 18 kilometres. In North Rhine-Westphalia, more than 30 people were injured, mainly by falling roof slates and chimneys.

12. What does epicentre mean?

The epicentre is located on the Earth's surface directly above an earthquake's hypocentre. This is the place in the Earth's crust where the fracture begins to spread across the fracture face.

13. What is the intensity of an earthquake?

Earthquake research uses two scales to classify earthquakes and earthquake tremors. They are often confused. The magnitude scale is a measure of the energy released during the fracture process at the quake's hypocentre. In contrast to this, the intensity scale classifies the shocks/vibrations at any given location on the Earth's surface according to the type of vibration as perceived by people and the degree of earthquake damage. This intensity scale (sometimes also abbreviated according to its authors' names to MSK or MM or - in the latest version for Europe - to EMS98) divides earthquakes into 12 classes. An intensity of 12 on this scale corresponds to total destruction. If the corresponding maximum vibrations do not apply for an indefinite distance from the quake's hypocentre but rather for the area directly above the hypocentre, at the so-called epicentre, then one speaks of the so-called I0 epicentral intensity. As a rule, it is the greatest intensity observed in an earthquake. Because of its spatial nature, the earthquake intensity scale is comparable to the Beaufort wind force scale, which also consists of 12 classes - from "Calm" to "Hurricane force".

14. What is "earthquake magnitude"?

Magnitude is the logarithmic measure of the seismic energy released by an earthquake at its hypocentre. To determine the magnitude, the ground movements must be recorded as seismograms using seismometers. An increase in magnitude of one unit corresponds to an increase in ground movement by a factor of 10 and increase in energy roughly to the power of thirty. Whereas the magnitude is a measure of the energy released in the earthquake's hypocentre, the intensity classifies the vibrations at any given location on the Earth's surface.

15. What is a Richter scale?

It is a magnitude scale designed by the American seismologist Charles Francis Richter in 1935 for California. It ranks the ground motion of the primary waves measured with a spe­cial seismograph (Wood Anderson seismograph) on a logarithmic scale. The Richter scale was originally defined for stations at a distance of a few hundred kilometres. In the following years further magnitude scales were developed to include stations at greater distances and sometimes analyse other wave types.

16. What was the strongest earthquake ever recorded?

The Shaanxi earthquake in China in 1556 is considered the most devastating quake in human history, with a death toll of approximately 830,000 and an estimated magnitude of 8. The strongest quake in the last hundred years took place in Chile on 22 May 1960 with a (moment) magnitude of 9.5. On 28 March 1964, a magnitude 9.1 quake shook the Prince William Sound in Alaska. Further strong quakes occurred on 26 December 2004 off the north-eastern coast of Indonesia in the Indian Ocean with a magnitude of 9.2, and on 11 March 2010 in the Pacific Ocean off the east coast of Japan with a magnitude of 9.0. All four events took place below the sea and triggered devastating tsunamis.

17. Which magnitude values can be distinguished from each other?

Local earthquake magnitude (ML) is determined on the basis of the primary waves from only relatively close stations. Normally this magnitude scale applies to distances of up to several hundred kilometres between the earthquake and the station. In contrast to this, the body wave magnitude (mb) uses seismic waves travelling through the deep interior of the Earth that are recorded by stations at distances of over 2,000 km. This magnitude is always determined very quickly. However, for strong earthquakes (> 6 mb), the bodywave magnitude is considered to be saturated, so that the magnitude hardly increases, even though the quake was a great deal stronger. Surface waves travel relatively slowly across the surface of the earth (velocities of some 3-4 km/s compared with 8-14 km/s for the body waves in the Earth's interior), but they can still be measured well at large distances from the hypocentre. The surface-wave magnitude (MS) determined from these waves only saturates during stronger events and was used for a long time to characterise strong quakes. However, the slow propagation speed means that the MS only becomes available some time after the event. Nowadays, earthquakes and stronger quakes are characterised primarily by the moment magnitude (Mw) that no longer saturates and can be linked directly with the physical parameters of the hypocentre. To determine this magnitude, theoretical seismograms are usually computed for the Earth and compared with observations. In the case of strong quakes, surface waves are mostly compared with each other, which is why the Mw value also cannot be made available immediately after the event.

18. Are earthquake-proof building structures possible?

The use of steel beams in construction work in earthquake hazard regions has distinct ad­vantages. However, complete protection from earthquakes does not exist. Nevertheless, suitable construction measures help to considerably reduce the danger of a structure col­lapsing, even in the event of strong earthquakes. There are no worldwide standards, but at least for Europe the requirements on the design of earthquake-resistant structures have been summarised (EUROCODE 8). Safety standards have been defined for high-rise build­ings, bridges, pipelines, towers and stacks.

19. Why can the ground liquefy due to an earthquake?

Soil liquefaction is a physical phenomenon related to a complete loss of shear resistance.

Granular loose material like sand undergoes a rapid compaction when shaken. If this material is saturated, in the compaction leads to a rapid pore pressure increase. As a result the water attempts to flow out from the soil towards the ground surface. The deformation associated with liquefaction goes from being very limited to huge lateral displacements and vertical disruptions.  Liquefaction mainly affects young geological formations, poorly consolidated deposits such as alluvial and littoral formations and also man-made landfills.

The effect of liquefaction can be reproduced, for example, by kicking a couple of times the sand close to the shoreline making this mechanically stressed area flabby. Experts call this liquefaction, thixotropy.

Even a strong (although not Major Great) earthquake like the 6.2 quake in 2011 in Christchurch, New Zealand caused an enormous damage by ground liquefactions. Some buildings collapsed or were uninhabitable due to the invading mudflow.

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Earthquakes

Earthquakes happen every day, but most are so small that humans cannot feel them. Nonetheless, over the past 50 years, earthquakes and the tsunamis and landslides that resulted from them have contributed to millions of injuries and deaths and more than $1 trillion in damage. For nearly a century, Caltech scientists and engineers have led the world in earthquake measurement and monitoring. By informing preparedness and response initiatives, and pioneering innovations in early warning, their work aims to reduce the human toll of these natural disasters. Learn more about earthquake science and engineering.

Earthquakes Terms to Know >

What Happens During an Earthquake?

What causes earthquakes, and what types of earthquakes are there? To answer these questions, it is first helpful to have an understanding of Earth's composition.

How Are Earthquakes Measured?

Two different viewpoints underpin the most important measurements related to earthquakes: magnitude and intensity . To scientists, an earthquake is an event inside the earth. To the rest of us, it is an extraordinary movement of the ground. Magnitude measures the former, while intensity measures the latter.

Can Seismologists Predict Earthquakes?

It is not currently possible to predict exactly when and where an earthquake will occur, nor how large it will be. However, seismologists can estimate where earthquakes may be likely to strike by calculating probabilities and forecasts .

How Could a Major Earthquake Affect Urban Infrastructure?

Megacities are especially vulnerable to earthquakes. Learn about cascading effects and how modeling can minimize the risk of a natural hazard turning into a disaster.

What Happens to Buildings During Earthquakes?

Find out how earthquakes affect houses, high-rises, and other buildings, and which are considered the safest and most dangerous places to be.

How Do We Know What Makes a Building Earthquake Resistant?

Learn how the Community Seismic Network gathers data about how the ground and buildings move to inform safer construction and better damage detection.

EARTHQUAKE PREPAREDNESS

How Do Earthquake Early Warning Systems Work?

Earthquake early warning systems don't predict earthquakes. Instead, they detect ground motion as soon as an earthquake begins and quickly send alerts that a tremor is on its way, giving people crucial seconds to prepare.

What Should You Do Before, During, and After an Earthquake?

It is impossible to predict when and where an earthquake will strike. Nonetheless, you can take steps before, during, and after a quake to help yourself stay safe and recover quickly.

Ask a Caltech Expert

Lucy Jones on Earthquakes

Find answers to common questions about earthquakes from seismologist and science communicator Lucy Jones, a visiting associate in geophysics at Caltech and the founder of the Dr. Lucy Jones Center for Science and Society.

Terms to Know

A smaller earthquake that occurs after the largest event of an earthquake sequence (mainshock). Aftershocks can occur for days, months, or years after the mainshock, but reduce in frequency over time.

Dip-slip fault

Fault where the two sides have moved vertically relative to each other.

Earthquake early warning (EEW) systems

When significant earthquakes begin, these systems distribute electronic alerts to warn people before shaking reaches them, providing potentially crucial seconds of preparation time.

Earthquake forecast

The probability of an earthquake of a certain size happening within a certain period of time. This is different from an earthquake "prediction," which requires a specific date and time, location, and magnitude. It is not yet possible to predict earthquakes.

The point on the surface of the earth directly above where an earthquake rupture begins.

A fracture in earth's crust. On either side of a fault, blocks of crust have moved relative to each other. Earthquakes occur when rock on one side of the fault suddenly slips.

An earthquake that comes before a larger earthquake in the same sequence. Foreshocks do not show any identifying characteristics when they occur; they are identified when a larger event follows.

For a given earthquake, the location within Earth's interior where the earthquake rupture starts

The severity of an earthquake in terms of what people and structures experience. A single earthquake has different intensities in different places.

The overall size of an earthquake, based on measurements of seismic waves recorded by seismographs. One earthquake may be felt at various intensities in different places, but it has only one magnitude.

The largest earthquake in a sequence. Mainshocks are sometimes preceded by foreshocks, and always followed by aftershocks.

Moment magnitude scale

A measure of earthquake magnitude based on the area of fault that moved, the amount that it moved, and the friction between the rocks. Developed by Caltech's Hiroo Kanamori and seismologist Thomas C. Hanks, this is the only method of measuring magnitude that is uniformly applicable to all sizes of earthquakes, but it is more difficult to compute than other scales.

Richter scale

A measure of earthquake magnitude based on seismic wave amplitudes that was introduced in 1935 by Caltech seismologists Charles Richter and Beno Gutenberg. The term is used colloquially to reference magnitude of any kind despite the fact that other magnitude scales, such as moment magnitude, are more commonly used today.

The squiggle-shaped record of ground motion collected by a seismometer.

Seismometer

A precise motion sensor used to record vibrations in the ground, such as seismic waves from earthquakes. Also known as a seismograph.

Strike-slip fault

Fault where the two sides have moved horizontally relative to each other.

Tectonic plates

Large, rigid pieces of the earth's crust that move relative to one another. Places where tectonic plates meet experience more earthquakes.

Thrust fault

Faults that occur in areas of Earth's crust where one slab of rock compresses against another, sliding up and over it during an earthquake. Thrust faults have been the sites of some of the world's largest quakes.

A series of earthquakes with no distinct mainshock occurring in a single area in a short period of time.

Dive Deeper

More Caltech Earthquake Research Coverage

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Shaking up earthquake research at MIT

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Major environmental events write their own headlines. With loss of life and crippling infrastructure damage, the aftershocks of earthquakes reverberate around the world — not only as seismic waves, but also in the photos and news stories that follow a major seismic event. So, it is no wonder that both scientists and the public are keen to understand the dynamics of faults and their hazard potential, with the ultimate goal of prediction.

To do this, William Frank and Camilla Cattania, assistant professors in MIT’s Department of Earth, Atmospheric and Planetary Sciences (EAPS), have teamed up as EQSci@MIT to uncover hidden earthquake behaviors and fault complexity, through observation, statistics, and modeling. Together, their complementary avenues of research are helping to expose the fault mechanics underpinning everything from aseismic events, like slow slip actions that occur over periods of hours or months, to large magnitude earthquakes that strike in seconds. They’re also looking at the ways tectonic regions interact with neighboring events to better understand how faults and seismic events evolve — and, in the process, shedding light on how frequently and predictably these events might occur.

“Basically, [we’re] trying to build together a pipeline from observations through modeling to answer the big-picture questions,” says Frank. “When we actually observe something, what does that mean for the big-picture result, in places where we have strong heterogeneity and lots of earthquake activity?”

Observing Earth as it creeps

While there are many ways to investigate different types of earthquakes and faults, Frank takes a detailed and steady approach: looking at slow-moving, low wave frequency earthquakes — called slow slip — in subduction zones over long periods of time. These events tend to go unnoticed by the public and lack an obvious seismic wave signature that would be registered by seismometers. However, they play a significant role in tectonic buildup and release of energy. “When we start to look at the size of these slow slip events, we realize that they are just as big as earthquakes,” says Frank.

His group leverages geodetic data, like GPS, to monitor how the ground moves on and near a fault to reveal what’s happening along the plate interface as you descend deeper underground. In the crust, near the surface, the plates tend to be locked together along the boundary, building up pressure and then releasing it as a giant earthquake. However, below that region, Frank says, the rocks are more elastic and can deform and creep, which can be picked up on instrumentation. “There are events that are transient. They happen over a set period of time, just like an earthquake, but instead of several seconds to minutes, they last several days to months,” he says.

Since slow slip has the capacity to cause energy loading in subduction zones through both stress and release, Frank and his group want to understand how slow earthquakes interact with seismic regions, where there’s potential for a large earthquake. By digging into observational data, from long-term readings to those taken on the scale of a few hours, Frank has learned that often there are many tiny earthquakes that repeat during slow slip. While a first glance at the data may look like just noise, clear signals emerge on closer inspection that reveal a lot about the subsurface plate interface — like the presence of trapped fluid, and how subduction zones behave at different locations along a fault.

“If we really want to understand where and when and how we're going to have a big earthquake, you have to understand what's happening around it,” says Frank, who has projects spread out around the globe, investigating subducting plate boundaries from Japan to the Pacific Northwest, and all the way to Antarctica.

Modeling complexity

Camilla Cattania’s work provides a counterpoint for Frank’s. Where the Frank group incorporates seismic and geodetic record collection, Cattania employs numerical, analytical, and statistical tools to understand the physics of earthquakes. Through modeling, her team can test hypotheses and then look for corroborating evidence in the field, or vice versa, using collected data to inform and refine models. Influenced by major seismic hazards in her home country of Italy, Cattania is keenly interested in the potential to contribute models for practical use in earthquake forecasting.

One aspect of her work has been to reconcile theoretical models with the complex reality of fault geometry. Each fault has its own physical characteristics that affect its behavior and can evolve over time — not just the dimensions of the fault, but also factors like the orientation of the rock fractures, the elastic properties of the rocks, and the irregularity and roughness of their surfaces. When looking into numerical models of aftershock sequences, she was able to show that they weren’t as predictive as statistical models because previous models were using idealized fault planes in the calculations.

To remedy this, Cattania explored ways to incorporate fault geometry that's more consistent with the complexity found in nature. “We were the first to implement this in a systematic way and then compare it to statistical models, and … to show that these physical models can do well, if you make them realistic enough,” she says.

Cattania has also been looking into modeling how the physical properties of faults control the frequency and size of earthquakes — a key question in understanding the hazards they pose. Some earthquake sequences tend to recur at intervals, but most don’t, defying easy prediction. In trying to understand why this is, Cattania explains, size is everything. “It turns out that periodicity is a property which depends on the size of the earthquake. It's much more unlikely to get periodic behavior for a large earthquake than it is for a small one, and it just comes out of the fundamental physics of how friction and elasticity control the cycle,” she says.

A synergistic approach

Ultimately, through their collaboration in EAPS at MIT, Frank and Cattania are trying to build more communication between observation and modeling in order to foster more rapid advancements in earthquake science. “Ever-improving seismic and geodetic measurements, together with new data analysis techniques, are providing unprecedented opportunities to probe fault behavior,” says Cattania. “With numerical models and theory, we try to explain why faults slip the way they do, and the best way to make progress is for modelers and observationalists to talk to each other.”

“What I really like about observational geophysics, and for my science to be useful, is collaborating and interacting with many different people,” says Frank. “Part of that is bringing together the different observational approaches and the constraints that we can generate, and [then] communicating our results to the modelers. More often than not, there's not as much communication as we'd like [between the groups]; so I’m super excited about Camilla being here.”

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National Earthquake Resilience: Research, Implementation, and Outreach (2011)

Chapter: 1 introduction.

1 Introduction

When a strong earthquake hits an urban area, structures collapse, people are injured or killed, infrastructure is disrupted, and business interruption begins. The immediate impacts caused by an earthquake can be devastating to a community, challenging it to launch rescue efforts, restore essential services, and initiate the process of recovery. The ability of a community to recover from such a disaster reflects its resilience, and it is the many factors that contribute to earthquake resilience that are the focus of this report. Specifically, we provide a roadmap for building community resilience within the context of the Strategic Plan of the National Earthquake Hazards Reduction Program (NEHRP), a program first authorized by Congress in 1977 to coordinate the efforts of four federal agencies—National Institute of Standards and Technology (NIST), Federal Emergency Management Agency (FEMA), National Science Foundation (NSF), and U.S. Geological Survey (USGS).

The three most recent earthquake disasters in the United States all occurred in California—in 1994 near Los Angeles at Northridge, in 1989 near San Francisco centered on Loma Prieta, and in 1971 near Los Angeles at San Fernando. In each earthquake, large buildings and major highways were heavily damaged or collapsed and the economic activity in the afflicted area was severely disrupted. Remarkably, despite the severity of damage, deaths numbered fewer than a hundred for each event. Moreover, in a matter of days or weeks, these communities had restored many essential services or worked around major problems, completed rescue efforts, and economic activity—although impaired—had begun to recover. It could be argued that these communities were, in fact, quite resilient. But

it should be emphasized that each of these earthquakes was only moderate to strong in size, less than magnitude-7, and that the impacted areas were limited in size. How well would these communities cope with a magnitude-8 earthquake? What lessons can be drawn from the resilience demonstrated for a moderate earthquake in preparing for a great one?

Perhaps experience in dealing with hurricane disasters would be instructive in this regard. In a typical year, a few destructive hurricanes make landfall in the United States. Most of them cause moderate structural damage, some flooding, limited disruption of services—usually loss of power—and within a few days, activity returns to near normal. However, when Hurricane Katrina struck the New Orleans region in 2005 and caused massive flooding and long-term evacuation of much of the population, the response capabilities were stretched beyond their limits. Few observers would argue that New Orleans, at least in the short term, was a resilient community in the face of that event.

Would an earthquake on the scale of the 1906 event in northern California or the 1857 event in southern California lead to a similar catastrophe? It is likely that an earthquake on the scale of these events in California would indeed lead to a catastrophe similar to hurricane Katrina, but of a significantly different nature. Flooding, of course, would not be the main hazard, but substantial casualties, collapse of structures, fires, and economic disruption could be of great consequence. Similarly, what would happen if there were to be a repeat of the New Madrid earthquakes of 1811-1812, in view of the vulnerability of the many bridges and chemical facilities in the region and the substantial barge traffic on the Mississippi River? Or, consider the impact if an earthquake like the 1886 Charleston tremor struck in other areas in the central or eastern United States, where earthquake-prone, unreinforced masonry structures abound and earthquake preparedness is not a prime concern? The resilience of communities and regions, and the steps—or roadmap—that could be taken to ensure that areas at risk become earthquake resilient, are the subject of this report.

EARTHQUAKE RISK AND HAZARD

Earthquakes proceed as cascades, in which the primary effects of faulting and ground shaking induce secondary effects such as landslides, liquefaction, and tsunami, which in turn set off destructive processes within the built environment such as fires and dam failures (NRC, 2003). The socioeconomic effects of large earthquakes can reverberate for decades.

The seismic hazard for a specified site is a probabilistic forecast of how intense the earthquake effects will be at that site. In contrast, seismic risk is a probabilistic forecast of the damage to society that will be caused by earthquakes, usually measured in terms of casualties and economic losses in a

specified area integrated over the post-earthquake period. Risk depends on the hazard, but it is compounded by a community’s exposure —its population and the extent and density of its built environment—as well as the fragility of its built environment, population, and socioeconomic systems to seismic hazards. Exposure and fragility contribute to vulnerability . Risk is lowered by resiliency , the measure of how efficiently and how quickly a community can recover from earthquake damage.

Risk analysis seeks to quantify the risk equation in a framework that allows the impact of political policies and economic investments to be evaluated, to inform the decision-making processes that contribute to risk reduction. Risk quantification is a difficult problem, because it requires detailed knowledge of the natural and the built environments, as well as an understanding of both earthquake and human behaviors. Moreover, national risk is a dynamic concept because of the exponential rise in the urban exposure to seismic hazards (EERI, 2003b)—calculating risk involves predictions of highly uncertain demographic trends.

Estimating Losses from Earthquakes

The synoptic earthquake risk studies needed for policy formulation are the responsibility of NEHRP. These studies can take the form of deterministic or scenario studies where the effects of a single earthquake are modeled, or probabilistic studies that weight the effects from a number of different earthquake scenarios by the annual likelihood of their occurrence. The consequences are measured in terms of dollars of damage, fatalities, injuries, tons of debris generated, ecological damage, etc. The exposure period may be defined as the design lifetime of a building or some other period of interest (e.g., 50 years). Typically, seismic risk estimates are presented in terms of an exceedance probability (EP) curve (Kunreuther et al., 2004), which shows the probability that specific parameters will equal or exceed specified values ( Figure 1.1 ). On this figure, a loss estimate calculated for a specific scenario earthquake is represented by a horizontal slice through the EP curve, while estimates of annualized losses from earthquakes are portrayed by the area under the EP curve.

The 2008 Great California ShakeOut exercise in southern California is an example of a scenario study that describes what would happen during and after a magnitude-7.8 earthquake on the southernmost 300 km of the San Andreas Fault ( Figure 1.2 ), a plausible event on the fault that is most likely to produce a major earthquake. Analysis of the 2008 ShakeOut scenario, which involved more than 5,000 emergency responders and the participation of more than 5.5 million citizens, indicated that the scenario earthquake would have resulted in an estimated 1,800 fatalities, $113 billion in damages to buildings and lifelines, and nearly $70 billion in busi-

FIGURE 1.1 Sample mean EP curve, showing that for a specified event the probability of insured losses exceeding L i is given by p i . SOURCE: Kunreuther et al. (2004).

ness interruption (Jones et al., 2008; Rose et al., in press). The broad areal extent and long duration of water service outages was the main contributor to business interruption losses. Moreover, the scenario is essentially a compound event like Hurricane Katrina, with the projected urban fires caused by gas main breaks and other types of induced accidents projected to cause $40 billion of the property damage and more than $22 billion of the business interruption. Devastating fires occurred in the wake of the 1906 San Francisco, 1923 Tokyo, and 1995 Kobe earthquakes.

Loss estimates have been published for a range of earthquake scenarios based on historic events—e.g., the 1906 San Francisco earthquake (Kircher et al., 2006); the 1811/1812 New Madrid earthquakes (Elnashai et al., 2009); and the magnitude-9 Cascadia subduction earthquake of 1700 (CREW, 2005)—or inferred from geologic data that show the magnitudes and locations of prehistoric fault ruptures (e.g., the Puente Hills blind thrust that runs beneath central Los Angeles; Field et al., 2005). In all cases, the results from such estimates are staggering, with economic losses that run into the hundreds of billions of dollars.

FEMA’s latest estimate of Annualized Earthquake Loss (AEL) for the nation (FEMA, 2008) is an example of a probabilistic study—an estimate of national earthquake risk that used HAZUS-MH software ( Box 1.1 ) together with input from Census 2000 data and the 2002 USGS National Seismic Hazard Map. The current AEL estimate of $5.3 billion (2005$)

FIGURE 1.2 A “ShakeMap” representing the shaking produced by the scenario earthquake on which the Great California ShakeOut was based. The colors represent the Modified Mercalli Intensity, with warmer colors representing areas of greater damage. SOURCE: USGS. Available at earthquake.usgs.gov/earthquakes/shakemap/sc/shake/ShakeOut2_full_se/ .

reflects building-related direct economic losses including damage to buildings and their contents, commercial inventories, as well as damaged building-related income losses (e.g., wage losses, relocation costs, rental income losses, etc.), but does not include indirect economic losses or losses to lifeline systems. For comparison, the Earthquake Engineering Research Institute (EERI) (2003b) extrapolated the FEMA (2001) estimate of AEL ($4.4 billion) for residential and commercial building-related direct economic losses by a factor of 2.5 to include indirect economic losses, the social costs of death and injury, as well as direct and indirect losses to the

BOX 1.1 HAZUS ® —Risk Metrics for NEHRP

The ability to monitor and compare seismic risk across states and regions is critical to the management of NEHRP. At the state and local level, an understanding of seismic risk is important for planning and for evaluating costs and benefits associated with building codes, as well as a variety of other prevention measures. HAZUS is Geographic Information System (GIS) software for earthquake loss estimation that was developed by FEMA in cooperation with the National Institute of Building Sciences (NIBS). HAZUS-MH (Hazards U.S.-Multi-Hazard) was released in 2003 to include wind and flood hazards in addition to the earthquake hazards that were the subject of the 1997 and 1999 HAZUS releases. Successive HAZUS maintenance releases (MR) have been made available by FEMA since the initial HAZUS-MH MR-1 release; the latest version, HAZUS-MH MR-5, was released in December 2010.

Annualized Earthquake Loss (AEL) is the estimated long-term average of earthquake losses in any given year for a specific location. Studies by FEMA based on the 1990 and 2000 censuses provide two “snapshots” of seismic risk in the United States (FEMA, 2001, 2008). These studies, together with an earlier analysis of the 1970 census by Petak and Atkisson (1982), show that the estimated national AEL increased from $781 million (1970$) to $4.7 billion (2000$)—or by about 40 percent—over four decades ( Figure 1.3 ). All three studies used building-related direct economic losses and included structural and nonstructural replacement costs, contents damage, business inventory losses, and direct business interruption losses.

industrial, manufacturing, transportation, and utility sectors to arrive at an annual average financial loss in excess of $10 billion.

Although the need to address earthquake risk is now accepted in many communities, the ability to identify and act on specific hazard and risk issues can be improved by reducing the uncertainties in the risk equation. Large ranges in loss estimates generally stem from two types of uncertainty—the natural variability assigned to earthquake processes ( aleatory uncertainty ), as well as a lack of knowledge of the true hazards and risks involved ( epistemic uncertainty ). Uncertainties are associated with the methodologies, the assumptions, and databases used to estimate the ground motions and building inventories, the modeling of building responses, and the correlation of expected economic and social losses to the estimated physical damages.

FIGURE 1.3 Growth of seismic risk in the United States. Annualized Earthquake Loss (AEL) estimates are shown for the census year on which the estimate is based, in census year dollars. Estimate for 1970 census from Petak and Atkinson (1982); HAZUS-99 estimate for 1990 census from FEMA (2001); and HAZUS-MH estimate for 2000 census from FEMA (2008). Consumer Price Index (CPI) dollar adjustments based on CPI inflation calculator (see data.bls.gov/cgi-bin/cpicalc.pl ).

Comparison of published risk estimates reveals the sensitivity of such estimates to varying inputs, such as soil types and ground motion attenuation models, or building stock inventories and damage calculations. The basic earth science and geotechnical research and data that the NEHRP agencies provide to communities help to reduce these types of epistemic uncertainty, whereas an understanding of the intrinsic aleatory uncertainty is achieved through scientific research into the processes that cause earthquakes. Accurate loss estimation models increase public confidence in making seismic risk management decisions. Until the uncertainties surrounding the EP curve in Figure 1.1 are reduced, there will be either unnecessary or insufficient emergency response planning and mitigation because the experts in these areas will be unable to inform decision-makers of the probabilities and potential outcomes with an appropriate degree of

confidence (NRC, 2006a). Information about new and rehabilitated buildings and infrastructure, coupled with improved seismic hazard maps, can allow policy-makers to track incremental reductions in risk and improvements in safety through earthquake mitigation programs (NRC, 2006b).

NEHRP ACCOMPLISHMENTS—THE PAST 30 YEARS

In its 30 years of existence, NEHRP has provided a focused, coordinated effort toward developing a knowledge base for addressing the earthquake threat. The following summary of specific accomplishments from the earth sciences and engineering fields are based on the 2008 NEHRP Strategic Plan (NIST, 2008):

• Improved understanding of earthquake processes. Basic research and earthquake monitoring have significantly advanced the understanding of the geologic processes that cause earthquakes, the characteristics of earthquake faults, the nature of seismicity, and the propagation of seismic waves. This understanding has been incorporated into seismic hazard assessments, earthquake potential assessments, building codes and design criteria, rapid assessments of earthquake impacts, and scenarios for risk mitigation and response planning.

• Improved earthquake hazard assessment. Improvements in the National Seismic Hazard Maps have been developed through a scientifically defensible and repeatable process that involves peer input and review at regional and national levels by expert and user communities. Once based on six broad zones, they now are based on a grid of seismic hazard assessments at some 150,000 sites throughout the country. The new maps, first developed in 1996, are periodically updated and form the basis for the Design Ground Motion Maps used in the NEHRP Recommended Provisions for Seismic Regulations for New Buildings and Other Structures, the foundation for the seismic elements of model building codes.

• Improved earthquake risk assessment. Development of earthquake hazard- and risk-assessment techniques for use throughout the United States has improved awareness of earthquake impacts on communities. NEHRP funds have supported the development and continued refinement of HAZUS-MH. The successful NEHRP-supported integration of earthquake risk-assessment and loss-estimation methodologies with earthquake hazard assessments and notifications has provided significant benefits for both emergency response and community planning. Moreover, major advances in risk assessment and hazard loss estimation beyond what could be included in a software package for general users were developed by the three NSF-supported earthquake engineering centers.

• Improved earthquake safety in design and construction. Earthquake safety in new buildings has been greatly improved through the adoption, in whole or in part, of earthquake-resistant national model building codes by state and local governments in all 50 states. Development of advanced earthquake engineering technologies for use in design and construction has greatly improved the cost-effectiveness of earthquake-resistant design and construction while giving options with predicted decision consequences. These techniques include new methods for reducing the seismic risk associated with nonstructural components, base isolation methods for dissipating seismic energy in buildings, and performance-based design approaches.

• Improved earthquake safety for existing buildings. NEHRP-led research, development of engineering guidelines, and implementation activities associated with existing buildings have led to the first generation of consensus-based national standards for evaluating and rehabilitating existing buildings. This work provided the basis for two American Society of Civil Engineers (ASCE) standards documents: ASCE 31 (Seismic Evaluation of Existing Buildings) and ASCE 41 (Seismic Rehabilitation of Existing Buildings).

• Development of partnerships for public awareness and earthquake mitigation. NEHRP has developed and sustained partnerships with state and local governments, professional groups, and multi-state earthquake consortia to improve public awareness of the earthquake threat and support the development of sound earthquake mitigation policies.

• Improved development and dissemination of earthquake information. There is now a greatly increased body of earthquake-related information available to public- and private-sector officials and the general public. This comes through effective documentation, earthquake response exercises, learning-from-earthquake activities, publications on earthquake safety, training, education, and information on general earthquake phenomena and means to reduce their impact. Millions of earthquake preparedness handbooks have been delivered to at-risk populations, and many of these handbooks have been translated from English into languages most easily understood by large sectors of the population. NEHRP now maintains a website 1 that provides information on the program and communicates regularly with the earthquake professional community through the monthly electronic newsletter, Seismic Waves.

• Improved notification of earthquakes. The USGS National Earthquake Information Center and regional networks, all elements of the Advanced National Seismic System (ANSS), now provide earthquake

_________________

1 See www.nehrp.gov .

alerts describing a magnitude and location within a few minutes after an earthquake. The USGS PAGER system 2 provides estimates of the number of people and the names of cities exposed to shaking, with corresponding levels of impact shown by the Modified Mercalli Intensity scale and estimates of the number of fatalities and economic loss, following significant earthquakes worldwide ( Figure 1.4 ). When coupled with graphic ShakeMaps 3 showing the distribution and severity of ground shaking (e.g., Chapter 3 , Figure 3.2 ), this information is essential for effective emergency response, infrastructure management, and recovery planning.

• Expanded training and education of earthquake professionals. Thousands of graduates of U.S. colleges and universities have benefited from their involvement and experiences with NEHRP-supported research projects and training activities. Those graduates now form the nucleus of America’s earthquake professional community.

• Development of advanced data collection and research facilities. NEHRP took the lead in developing ANSS and the George E. Brown, Jr. Network for Earthquake Engineering Simulation (NEES). Through these initiatives, NEES now forms a national infrastructure for testing geotechnical, structural, and nonstructural systems, and once completed, ANSS will provide a comprehensive, nationwide system for monitoring seismicity and collecting data on earthquake shaking on the ground and in structures. NEHRP also has participated in the development of the Global Seismographic Network to provide data on seismic events worldwide.

As well as this list of important accomplishments cited in the 2008 NEHRP Strategic Plan, the following range of NEHRP accomplishments in the social science arena were described in NRC (2006a):

• Development of a comparative research framework. Largely supported by NEHRP, over the past three decades social scientists increasingly have placed the study of earthquakes within a comparative framework that includes other natural, technological, and willful events. This evolving framework calls for the integration of hazards and disaster research within the social sciences and among social science, natural science, and engineering disciplines.

• Documentation of community and regional vulnerability to earthquakes and other natural hazards. Under NEHRP sponsorship, social science knowledge has expanded greatly in terms of data on community and regional exposure and vulnerability to earthquakes and other natural hazards, such that the foundation has been established for devel-

2 See earthquake.usgs.gov/earthquakes/pager/ .

3 See earthquake.usgs.gov/earthquakes/shakemap/ .

FIGURE 1.4 Sample PAGER output for the strong and damaging February 2011 earthquake in Christchurch, New Zealand. SOURCE: USGS. Available at earthquake.usgs.gov/earthquakes/pager/events/us/b0001igm/index.html .

oping more precise loss estimation models and related decision support tools (e.g., HAZUS). The vulnerabilities are increasingly documented through state-of-the-art geospatial and temporal methods (e.g., GIS, remote sensing, and visual overlays of hazardous areas with demographic information), and the resulting data are equally relevant to pre-, trans-, and post-disaster social science investigations.

• Household and business-sector adoption of self-protective measures. A solid knowledge base has been developed under NEHRP at the household level on vulnerability assessment, risk communication, warning response (e.g., evacuation), and the adoption of other forms of protective action (e.g., emergency food and water supplies, fire extinguishers, procedures and tools to cut off utilities, hazard insurance). Adoption of these and other self-protective measures has been modeled systematically, highlighting the importance of disaster experience and perceptions of personal risk (i.e., beliefs about household vulnerability to and consequences of specific events) and, to a lesser extent, demographic variables (e.g., income, education, home ownership) and social influences (e.g., communications patterns and observations of what other people are doing). Although research on adoption of self-protective measures of businesses is much more limited, recent experience of disaster-related business or lifeline interruptions has been shown to be correlated with greater preparedness activities, at least in the short run. Such preparedness activities are more likely to occur in larger as opposed to smaller commercial enterprises.

• Public-sector adoption of disaster mitigation measures. Most NEHRP-sponsored social science research has focused on the politics of hazard mitigation as they relate to intergovernmental issues in land-use regulations. The highly politicized nature of these regulations has been well documented, particularly when multiple layers of government are involved. Governmental conflicts regarding responsibility for the land-use practices of households and businesses are compounded by the involvement of other stakeholders (e.g., bankers, developers, industry associations, professional associations, other community activists, and emergency management practitioners). The results are complex social networks of power relationships that constrain the adoption of hazard mitigation policies and practices at local and regional levels.

• Hazard insurance issues. NEHRP-sponsored social research has documented many difficulties in developing and maintaining an actuarially sound insurance program for earthquakes and floods—those who are most likely to purchase earthquake and flood insurance are, in fact, those who are most likely to file claims. This problem makes it virtually impossible to sustain an insurance market in the private sector for these hazards. Economists and psychologists have documented in laboratory studies

a number of logical deficiencies in the way people process information related to risks as it relates to insurance decision-making. Market failure in earthquake and flood insurance remains an important social science research and public policy issue.

• Public-sector adoption of disaster emergency and recovery preparedness measures. NEHRP-sponsored social science studies of emergency preparedness have addressed the extent of local support for disaster preparedness, management strategies for improving the effectiveness of community preparedness, the increasing use of computer and communications technologies in disaster planning and training, the structure of community preparedness networks, and the effects of disaster preparedness on both pre-determined (e.g., improved warning response and evacuation behavior) and improvised (e.g., effective ad hoc uses of personnel and resources) responses during actual events. Thus far there has been little social science research on the disaster recovery aspect of preparedness.

• Social impacts of disasters. A solid body of social science research supported by NEHRP has documented the destructive impacts of disasters on residential dwellings and the processes people go through in housing recovery (emergency shelter, temporary sheltering, temporary housing, and permanent housing), as well as analogous impacts on businesses. Documented specifically are the problems faced by low-income households, which tend to be headed disproportionately by females and racial or ethnic minorities. Notably, there has been little social science research under NEHRP on the impacts of disasters on other aspects of the built environment. There is a substantial research literature on the psychological, social, and economic and (to a lesser extent) political impacts of disaster, which suggests that these impacts, while not random within impacted populations, are generally modest and transitory.

• Post-disaster responses by the public and private sectors. Research before and since the establishment of NEHRP in 1977 has contradicted misconceptions that during disasters, panic will be widespread, that large percentages of those who are expected to respond will simply abandon disaster relief roles, that local institutions will break down, that crime and other forms of anti-social behavior will be rampant, and that the mental impairment of victims and first responders will be a major problem. Existing and ongoing research is documenting and modeling the mix of expected and improvised responses by emergency management personnel, the public and private organizations of which they are members, and the multi-organizational networks within which these individual and organizational responses are nested. As a result of this research, a range of decision support tools is now being developed for emergency management practitioners.

• Post-disaster reconstruction and recovery by the public and private sectors. Prior to NEHRP relatively little was known about disas-

ter recovery processes and outcomes at different levels of analysis (e.g., households, neighborhoods, firms, communities, and regions). NEHRP-funded projects have helped to refine general conceptions of disaster recovery, made important contributions in understanding the recovery of households and communities (primarily) and businesses (more recently), and contributed to the development of statistically based community and regional models of post-disaster losses and recovery processes.

• Research on resilience has been a major theme of the NSF-supported earthquake research centers. The Multidisciplinary Center for Earthquake Engineering Research (MCEER) sponsored research providing operational definitions of resilience, measuring its cost and effectiveness, and designing policies to implement it at the level of the individual household, business, government, and nongovernment institution. The Mid-American Earthquake Center (MAE) sponsored research on the promotion of earthquake-resilient regions.

ROADMAP CONTEXT—THE EERI REPORT AND NEHRP STRATEGIC PLAN

The 2008 NEHRP Strategic Plan calls for an accelerated effort to develop community resilience. The plan defines a vision of “a nation that is earthquake resilient in public safety, economic strength, and national security,” and articulates the NEHRP mission “to develop, disseminate, and promote knowledge, tools, and practices for earthquake risk reduction—through coordinated, multidisciplinary, interagency partnerships among NEHRP agencies and their stakeholders—that improve the Nation’s earthquake resilience in public safety, economic, strength, and national security.” The plan identifies three goals with fourteen objectives (listed below), plus nine strategic priorities (presented in Appendix A ).

Goal A: Improve understanding of earthquake processes and impacts.

Objective 1: Advance understanding of earthquake phenomena and generation processes.

Objective 2: Advance understanding of earthquake effects on the built environment.

Objective 3: Advance understanding of the social, behavioral, and economic factors linked to implementing risk reduction and mitigation strategies in the public and private sectors.

Objective 4: Improve post-earthquake information acquisition and management.

Goal B: Develop cost-effective measures to reduce earthquake impacts on individuals, the built environment, and society-at-large.

Objective 5: Assess earthquake hazards for research and practical application.

Objective 6: Develop advanced loss estimation and risk assessment tools.

Objective 7: Develop tools that improve the seismic performance of buildings and other structures.

Objective 8: Develop tools that improve the seismic performance of critical infrastructure.

Goal C: Improve the earthquake resilience of communities nationwide.

Objective 9: Improve the accuracy, timeliness, and content of earthquake information products.

Objective 10: Develop comprehensive earthquake risk scenarios and risk assessments.

Objective 11: Support development of seismic standards and building codes and advocate their adoption and enforcement.

Objective 12: Promote the implementation of earthquake-resilient measures in professional practice and in private and public policies.

Objective 13: Increase public awareness of earthquake hazards and risks.

Objective 14: Develop the nation’s human resource base in earthquake safety fields.

Although the Strategic Plan does not specify the activities that would be required to reach its goals, in the initial briefing to the committee NIST, the NEHRP lead agency, described the 2003 report by the EERI, Securing Society Against Catastrophic Earthquake Losses, as at least a starting point. The EERI report lists specific activities—and estimates costs—for a range of research programs (presented in Appendix B ) that are in broad accord with the goals laid out in the 2008 NEHRP Strategic Plan. The committee was asked to review, update, and validate the programs and cost estimates laid out in the EERI report.

COMMITTEE CHARGE AND SCOPE OF THIS STUDY

The National Institute of Standards and Technology—the lead NEHRP agency—commissioned the National Research Council (NRC) to undertake a study to assess the activities, and their costs, that would be required for the nation to achieve earthquake resilience in 20 years ( Box 1.2 ). The charge

BOX 1.2 Statement of Task

A National Research Council committee will develop a roadmap for earthquake hazard and risk reduction in the United States. The committee will frame the road map around the goals and objectives for achieving national earthquake resilience in public safety and economic security stated in the current strategic plan of the National Earthquake Hazard Reduction Program (NEHRP) submitted to Congress in 2008. This roadmap will be based on an analysis of what will be required to realize the strategic plan’s major technical goals for earthquake resilience within 20 years. In particular, the committee will:

• Host a national workshop focused on assessing the basic and applied research, seismic monitoring, knowledge transfer, implementation, education, and outreach activities needed to achieve national earthquake resilience over a twenty-year period.

• Estimate program costs, on an annual basis, that will be required to implement the roadmap.

• Describe the future sustained activities, such as earthquake monitoring (both for research and for warning), education, and public outreach, which should continue following the 20-year period.

to the committee recognized that there would be a requirement for some sustained activities under the NEHRP program after this 20-year period.

To address the charge, the NRC assembled a committee of 12 experts with disciplinary expertise spanning earthquake and structural engineering; seismology, engineering geology, and earth system science; disaster and emergency management; and the social and economic components of resilience and disaster recovery. Committee biographic information is presented in Appendix C .

The committee held four meetings between May and December, 2009, convening twice in Washington, DC; and also in Irvine, CA; and Chicago, IL (see Appendix D ). The major focal point for community input to the committee was a 2-day open workshop held in August 2009, where concurrent breakout sessions interspersed with plenary addresses enabled the committee to gain a thorough understanding of community perspectives regarding program needs and priorities. Additional briefings by NEHRP agency representatives were presented during open sessions at the initial and final committee meetings.

Report Structure

Building on the 2008 NEHRP Strategic Plan and the EERI report, this report analyses the critical issues affecting resilience, identifies challenges and opportunities in achieving that goal, and recommends specific actions that would comprise a roadmap to community resilience. Because the concept of “resilience” is a fundamental tenet of the roadmap for realizing the major technical goals of the NEHRP Strategic Plan, Chapter 2 presents an analysis of the concept of resilience, a description of the characteristics of a resilient community, resilience metrics, and a description of the benefits to the nation of a resilience-based approach to hazard mitigation. Chapter 3 contains descriptions of the 18 broad, integrated tasks comprising the elements of a roadmap to achieve national earthquake resilience focusing on the specific outcomes that could be achieved in a 20-year timeframe, and the elements realizable within 5 years. These tasks are described in terms of the proposed activity and actions, existing knowledge and current capabilities, enabling requirements, and implementation issues. Costs to implement these 18 tasks are presented in Chapter 4 , in as much detail as possible within the constraint that some components have been the subject of specific, detailed costing exercises whereas others are necessarily broad-brush estimates at this stage. The final chapter briefly summarizes the major elements of the roadmap.

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The United States will certainly be subject to damaging earthquakes in the future. Some of these earthquakes will occur in highly populated and vulnerable areas. Coping with moderate earthquakes is not a reliable indicator of preparedness for a major earthquake in a populated area. The recent, disastrous, magnitude-9 earthquake that struck northern Japan demonstrates the threat that earthquakes pose. Moreover, the cascading nature of impacts-the earthquake causing a tsunami, cutting electrical power supplies, and stopping the pumps needed to cool nuclear reactors-demonstrates the potential complexity of an earthquake disaster. Such compound disasters can strike any earthquake-prone populated area. National Earthquake Resilience presents a roadmap for increasing our national resilience to earthquakes.

The National Earthquake Hazards Reduction Program (NEHRP) is the multi-agency program mandated by Congress to undertake activities to reduce the effects of future earthquakes in the United States. The National Institute of Standards and Technology (NIST)-the lead NEHRP agency-commissioned the National Research Council (NRC) to develop a roadmap for earthquake hazard and risk reduction in the United States that would be based on the goals and objectives for achieving national earthquake resilience described in the 2008 NEHRP Strategic Plan. National Earthquake Resilience does this by assessing the activities and costs that would be required for the nation to achieve earthquake resilience in 20 years.

National Earthquake Resilience interprets resilience broadly to incorporate engineering/science (physical), social/economic (behavioral), and institutional (governing) dimensions. Resilience encompasses both pre-disaster preparedness activities and post-disaster response. In combination, these will enhance the robustness of communities in all earthquake-vulnerable regions of our nation so that they can function adequately following damaging earthquakes. While National Earthquake Resilience is written primarily for the NEHRP, it also speaks to a broader audience of policy makers, earth scientists, and emergency managers.

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• Published: 09 December 2022

A multi-disciplinary view on earthquake science

Nature Communications volume  13 , Article number:  7331 ( 2022 ) Cite this article

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Earthquakes are a natural hazard affecting millions of people globally every year. Researchers are working on understanding the mechanisms of earthquakes and how we can predict them from various angles, such as experimental work, theoretical modeling, and machine learning. We invited Marie Violay (EPFL Lausanne), Annemarie Baltay (USGS), Bertrand Rouet-Leduc (Kyoto University) and David Kammer (ETH Zürich) to discuss how such a multi-disciplinary approach can advance our understanding of Earthquakes.

Can you give a brief overview of what your scientific work looks like and from what angle you approach Earthquakes?

Bertrand: My research on earthquakes is focused on the topics of earthquake nucleation and the interaction between slip modes - the way tectonic stress is released. A variety of slip modes exist, with dynamic earthquakes and creep at both ends of a spectrum that encompasses slow slip events of varied duration and scale. Many questions remain on the interplay between the members of this spectrum, including what may determine how and why a slow slip event may degenerate into an earthquake.

Marie: My research aims to understand the physics of fluid-induced earthquakes. Anthropogenic fluid injections during hydraulic fracturing, reservoir impoundment, the injection of waste water or CO2 storage can induce small stress perturbations in the underground and lead to fault reactivation and enhanced seismic activity. Moreover, long-lasting regular natural earthquake sequences are often associated with elevated pore fluid pressures at seismogenic depths. The mechanisms that govern the nucleation, propagation and recurrence of fluid-induced earthquakes are poorly constrained, and our ability to assess the seismic hazard that is associated with natural and induced events remains limited. At EPFL, we aim to improve our knowledge of fluid-induced earthquake mechanisms through multi-scale experimental approaches.

David: In my research, we aim to establish a fundamental understanding of tectonic fault ruptures as they occur during natural earthquakes. We develop theoretical and numerical models that describe the full cycle of an earthquake, including nucleation, propagation and arrest of the fault rupture, and help us to understand the mechanisms that govern earthquakes.

Annemarie: I am an observational earthquake scientist at the U.S. Geological Survey, using seismograms recorded at various distances from the earthquakes to probe what we know about both the earthquake source as well as how seismic waves propagate through Earth. I am interested in how both earthquakes and Earth control ground motions which are measured at distance, and how these reveal the earthquake source and path. I am particularly interested in earthquake stress drop, which is the amount of tectonic stress released during an earthquake rupture, and which can be estimated from the radiated seismic waves.

My research approaches these questions of earthquake nucleation and the interplay between slip modes from two angles: at multiple scales and using data science. I develop machine learning-based methods to detect seismic and geodetic signals from the scale of laboratory experiments, to the scale of subduction zones.

We apply cm-scale friction experiments to study the effect of fluid pressure on earthquake nucleation and propagation under crustal deformation conditions during the entire earthquake cycle. dm-scale dynamic rupture experiments are in turn applied on experimental faults to investigate the influence of fluid pressure on the nucleation and propagation of ruptures. Our analysis of post-mortem experimental faults is carried out with state-of-the-art microstructural techniques. We finally aim to calibrate the theoretical friction law with friction experiments and faulted rock microstructural observations.

We pursue our objectives along multiple research axes. First, we develop numerical methods that allow us to include more complexity into earthquake fault rupture models in order to build more realistic earthquake scenarios. Second, we calibrate our models with observations from friction experiments, as described by Marie, and use them to support the analysis of observations from large-scale laboratory earthquake experiments by giving access to quantities that are not easily measured in the experiments. Finally, we use our simulation results to develop fracture-mechanics-based theoretical models of laboratory earthquakes, which we then apply to upscale the knowledge gained from large-scale experiments to the field scale and natural earthquakes.

I further work on ground-motion models (GMMs) and their physical components and uncertainty. Reducing the latter, will ultimately lead to more precise and accurate seismic hazard maps. Currently, I am working towards physical explanations for variability in the source, site, and path components in ground motions. Ultimately, we will develop models for predicting those effects from geophysical observables, such as stress drop (for source), site velocity profiles and attenuation (for site), and whole-path attenuation (for path).

What are the most impactful recent advances in your communities and how do they add to the bigger picture in Earthquake science?

Bertrand: Recent physical models of the earthquake cycle and laboratory studies suggest earthquakes may nucleate during a preparatory aseismic phase of variable duration from minutes to years 1 , 2 , 3 , 4 . An aseismic phase is characterized through surface displacement, but the absence of notable earthquakes.

Thanks to increasing deployments of seismic and GPS stations, as well as the development of Interferometric Synthetic Aperture Radar (InSAR), the observation of such aseismic deformation is becoming common, from continuous aseismic slip 5 , 6 to week-long slow slip events 7 , 8 . The systematic observation of deformation events on faults is getting closer and may soon give definite answers on the interaction between slip modes and on earthquake nucleation.

Marie: Aseismic slip plays an important role for us as well - recent laboratory and natural observations suggest it to be one of the triggering mechanisms of fluid-induced earthquakes. Whereas other trigger mechanisms do exist as well, aseismic slip has an important role insofar that it can induce seismicity in regions beyond the fluid pressurized zone and hence potentially increase the seismic hazard area. Thus, it is critical for us to not only understand the mechanisms that cause fault slip, but also the conditions that lead to (a)seismic slip.

David : Our community is continuously pushing the theoretical and numerical approaches to create more realistic models for the full earthquake cycle. One important contribution in the large sense is the community code verification exercises 9 , in which various numerical codes are compared and benchmarked. This is a very important contribution to continue supporting rigor and reproducibility in our field, and I believe this will have long-lasting impact.

Annemarie : In earthquake seismology, we are starting to explore new ways to utilize the vast amounts of available data more efficiently. Novel machine learning (ML) techniques help us to improve our earthquake catalogs, in particular to understand seismic sequences for smaller and much more frequent events. ML is further applied to mine the ambient seismic wavefield to discover tectonic tremor which helps to track plate motions or map the Earth’s interior. This includes more effectively regressing instrumental records of moderate and large earthquakes which are spatially variable, to develop so-called non-ergodic ground-motion models, with increasing sophistication and customization; and even interpreting felt earthquake reports from citizen responders to get a better idea of how people experience shaking, a topic that we are currently working on now.

Other recent advances that I am personally very excited about are efforts to use numerical simulations to make theoretical models, which are often very simple, a degree more realistic, but in a fundamental way. A very nice example 10 , 11 is the development of theoretical models for elongated earthquake ruptures. Others include theoretical models for the propagation speed of frictional ruptures 12 , 13 , fluid-driven fault rupture 14 , 15 , and earthquake scaling 16 , 17 .

Finally, there are exciting efforts to enhance numerical simulations with more complexity, such as realistic fault geometry, multi-physical fault phenomena, and fault heterogeneity 18 , 19 , 20 , 21 , 22 .

What are the most pressing research questions your respective communities are working on at the moment?

Bertrand : Systematically observing deformation events on faults may well be key to understanding the interaction between modes of slip and earthquake nucleation, and might provide observables that may allow discriminating between a harmless slow slip event and an aseismic precursor to a major earthquake.

Marie: One major research task is to determine what controls the onset of dynamic instability, i.e. the competition between frictional aseimic preslip and fluid diffusion fronts. We further try to get a better handle on both what’s controlling the maximum magnitude of fluid-induced events, but also whether the maximum magnitude scales with a number of parameters (injected volume, the pre-stress, stress state, fault area, fluid injection rate, the compressibility of the fluid or a combination of these). A final question is whether heterogeneity enters into the scaling.

David: Physically speaking, there are many questions related to the earthquake cycle and the processes governing it. For instance, what is the exact nucleation process of an earthquake or how do natural fault ruptures arrest? Many of these questions are directly related to a need for a better understanding of fault friction properties (e.g., fracture energy) and multi-physical phenomena (e.g. pore pressure, temperature) under natural conditions, and for more information about fault heterogeneity and its effect on earthquake mechanics.

However, current geodetic methods cannot always resolve small (km-scale) day- to week-long events of slip, and doing so involves manual processing and analysis that cannot scale to the systematic and global observation of deformation events. Progress towards automatic detection of tectonic events, with recent successes from automatic detection of aseismic slip 23 to earthquakes 24 , is among the most pressing research topics in the quest towards a better understanding of the spectrum of slip modes, the interaction between slip modes, and earthquake nucleation.

From a theoretical perspective, there is an important question on reconciling observations from small-scale rock experiments, with large-scale laboratory earthquake experiments, and field observations. Can we build models that consolidate our knowledge from the lab with observations from the field?

Are there specific research questions you would like to see addressed by another community?

Bertrand : As progress towards automation of tectonic deformation is becoming a pressing issue to keep progressing towards a better understanding of earthquakes, the involvement of the data science and machine learning (ML) communities could make all the difference. Similar to how developments of ML for the life sciences have become ubiquitous, developments of ML specifically for the earth sciences will hopefully become another important area of applied ML research.

Marie: As an experimentalist we always try to make our measurements as precise and fast as possible, as close to the fault, and on as many points as possible. Digital image correlation allows fast and precise measurements of displacement for experiments performed without confining pressure. The development of distributed fiber optic measurement has just started to produce excellent results in pressure and temperature, and we intend to deepen our collaboration with this community.

David: As modelers we are always relying on experimental data for calibration and validation of our models (as a return we provide the opportunity of generalizing the experimental results). For this reason, more precise experimental observations of the local constitutive friction law at realistic conditions (e.g. high rupture speed and high contact pressure) would be very helpful. This is, of course, technically very challenging, but I would like to push for more direct collaboration between experimental and theoretical researchers, as this could lead to important progress in our fundamental understanding of earthquake mechanics.

Annemarie: As an observational earthquake seismologist, I think we need to strengthen our link in two directions -- earthquake simulations, both dynamic and kinematic, and laboratory experiments. In both of those cases, inputs such as stress, slip, dimension or material properties can be set and controlled, parameters which we have difficulty resolving in detail or with reliability observationally. We need to continue to validate the simulations, to ensure that they are capturing the correct physics and earth properties, and on the lab side, push the scale of experiments to bridge the link to in-situ earthquakes. Of course, the collaboration between all the disciplines is essential to ensure results and interpretations are brought together.

How would you like to see the link between earthquake policy and hazard mitigation strategies strengthened in regards to your research area?

Bertrand: In the not so distant future, tectonic deformation may be continuously monitored using data science and ML models on both seismic and geodetic data, notably yielding improved mappings of fault locking and slip budget, with the potential to inform and improve models of seismic hazard.

Marie: The reliability of natural hazard estimates needs to rely heavily on the definition of a faulting model, which needs to be underpinned by realistic physical constraints such as fault geometry, friction and rupture laws.

David: I agree that data-driven and ML approaches have the potential to support the process of determining the seismic hazard. As nicely pointed-out by Marie, the models should be constrained by physical considerations. In addition to those already mentioned, I would also include constraints based on fault rupture processes, such as energy balance, rupture mode, and propagation/arrest conditions.

Annemarie: As we continually refine and update our models of seismicity rates and occurrence, we have more detailed, specific, accurate models for seismic shaking, which also results in models that are more precise and less variable. Spatial and temporal dependence on finer scales could be incorporated into hazard and forecast products; in the case of USGS products such as Operational Aftershock Forecasting, we could give communities a more accurate and precise picture of what to expect after a large earthquake, which could quell anxiety and bring better preparedness.

This interview was conducted by Sebastian Müller.

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Earthquake preparedness of households and its predictors based on health belief model

• Masoumeh Rostami-Moez 1 , 2 ,
• Mohammad Rabiee-Yeganeh 2 ,
• Mohammadreza Shokouhi 3 ,
• Amin Dosti-Irani 1 , 4 &
• Forouzan Rezapur-Shahkolai   ORCID: orcid.org/0000-0001-5049-1109 5 , 6  

BMC Public Health volume  20 , Article number:  646 ( 2020 ) Cite this article

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Earthquakes are one of the most destructive natural disasters in which many people are injured, disabled, or died. Iran has only 1 % of the world’s population, but the percentage of its earthquake-related deaths is absolutely higher. Therefore, this study aimed to determine the level of earthquake preparedness of households and its predictors using the Health Belief Model (HBM).

This observational descriptive and analytical study was conducted on 933 households in Hamadan province, located in the west of Iran, in 2019. Multi-stage cluster random sampling was used for selecting the participants. The inclusion criteria were being at least 18 years old and being able to answer the questions. A questionnaire was used for data collection including earthquake preparedness, awareness of earthquake response, predictors of earthquake preparedness based on the HBM, and demographic information. Analysis of variance, independent t-test, and a linear regression model was used.

The mean age of participants was 38.24 ± 12.85 years. The average score of earthquake preparedness was low (approximately 30%). There was a significant relationship between earthquake preparedness and gender ( P  < 0.001), homeownership ( P  < 0.001), marriage status ( P  < 0.001), education ( P  < 0.001), and previous earthquake experience ( P  < 0.001). Regarding the HBM constructs, perceived benefits ( P  < 0.001), cues to action ( P  < 0.001), and self-efficacy ( P  < 0.001) were significant predictors of earthquake preparedness.

Conclusions

Earthquake preparedness was insufficient. Besides, perceived benefits, cues to action, and self-efficacy were predictors of earthquake preparedness. These predictors can be taken into account, for designing and implementing related future interventions.

Peer Review reports

Earthquakes are one of the most dangerous natural hazards that occur suddenly and uncontrollably. They cause physical, psychological, and social damages in human societies [ 1 ]. Over the past two decades, 800 million people have been injured by natural disasters. Besides, natural disasters have caused 42 million deaths in the world [ 2 ]. Iran is always at risk of earthquakes due to its geographical location on the Alpine-Himalayan orogenic belt [ 3 , 4 ]. More than 70% of the major cities in Iran are vulnerable to substantial damages. The earthquakes of recent decades have not only caused the deaths of thousands but also have caused massive economic damage and destroyed many cities and villages in the world [ 5 , 6 ]. Iran has only 1 % of the world’s population, but the percentage of its earthquake-related deaths is absolutely higher [ 7 ]. The disaster management cycle has four phases including mitigation, preparedness, response, and recovery. Preparedness is the most important phase in the disaster management cycle. Previous research in Iran has shown that the role of people as the most important and largest group has often been neglected in disaster preparedness program planning [ 8 ].

The Health Belief Model (HBM) describes the decision-making process that individuals use to adopt healthy behavior. It can be an effective framework for developing health promotion strategies [ 9 ]. Theoretically, in the HBM, perceived susceptibility, perceived severity, perceived benefits, perceived barriers, cues to action, and self-efficacy (the beliefs of individuals in their ability to prepare for disaster) predict behavior [ 1 , 9 , 10 ].

There are some studies on earthquake preparedness that have assessed the readiness of individuals based on their knowledge and skills [ 11 , 12 , 13 , 14 , 15 ]. Some studies have also considered structural and non-structural safety in some cities [ 16 ] and some studies have investigated students’ readiness [ 17 , 18 ]. There are a few studies that have used behavioral change models in the disaster area [ 5 ]. The Haraoka and Inal used the Health Belief Model to develop a questionnaire for earthquake preparedness [ 1 , 11 ].

Previous studies in Iran showed that most households did not have enough readiness and had a relatively high vulnerability to possible earthquake hazards [ 19 , 20 ]. Also, one study showed that improving the socio-economic status was correlated with improving the attitude of people about disaster preparedness [ 13 ]. In DeYoung et al.ʼs study, earthquake readiness was positively correlated with risk perception, self-efficacy, and trust in information about hazards through media [ 21 ].

To the best of the authors’ knowledge, this is the first study in Iran that examines earthquake preparedness of households, using a behavior change model. Considering the importance of earthquake preparedness of households, this study aims to asses the level of earthquake preparedness of households and its predictors based on HBM.

Study design and participants

This observational descriptive and analytical study was carried out in all counties of Hamadan province, located in the west of Iran, in 2019. These counties includes Hamadan (the capital of Hamadan province), Malayer, Tuyserkan, Nahavand, Razan, Bahar, Kabudarahang, Asadabad, and Famenin. Based on the previous study [ 19 ], the estimated sample size was 600 households. Cluster sampling was used for this study and we used the design effect of 1.5 plus 10% attrition. Subsequently, the final sample size was calculated at 1000 households. The data were collected from February to July 2019. From each county, a university graduate person was recruited and trained for data collection. The supervision and training were done by the first author. The verbal informed consent was obtained from all participants before the data gathering. The participants were first provided a description of the study and they were informed that the participation in the study was voluntary, and all study data were anonymous and confidential. Then, if they gave verbal informed consent, they would participate in the study and fill out the anonymous questionnaires. A person aged 18 or above was randomly selected from each household and answered the questions. For illiterate people, questionnaires were filled out through interviewing them. The inclusion criteria were being at least 18 years old and being able to answer the questions. The exclusion criteria were an incomplete questionnaire.

Participants have been selected by multi-stage cluster random sampling. First, stratified sampling was used for each county based on its urban and rural populations. Then, in urban and rural areas, a list of urban or rural health centers was listed and one health center was randomly selected in each county. After that, from the list of all households covered by the selected health center, one household was selected by simple random sampling and sampling started taking the clockwise direction of the selected household and continued until the required sample was collected. For selecting the sample of the urban population of Hamadan County, we selected one health center from each district by simple random sampling (in Hamadan city, there are four districts). In the next stage, from the list of covered households, one household was randomly selected and the sampling was started taking the clockwise direction until the required sample in each district was collected.

Measurements

The questionnaire used for data collection comprises four domains including 1) demographics, 2) earthquake preparedness 3) awareness on earthquake response, and 4) predictor of earthquake preparedness based on the HBM. Earthquake preparedness was response variable.

Demographics included age, sex, occupation, education, economic status, family size, number of individuals over 60 years old and under 16, earthquake experience, homeownership, marital status, and having a person with a disease that needs medication at their home.

We measured earthquake preparedness by an earthquake preparedness checklist [ 22 ]. This checklist was developed and validated by Spittal et al., in 2006. It consists of 23 questions with yes or no answers. The questions are about: having a working torch (flashlight), a first aid kit, a working battery radio, a working fire extinguisher, etc. [ 22 ]. We adapted this checklist by adding two items according to the context of the study. These two questions were: 1) do you know the necessary contact numbers such as fire station, police, and emergency so that you will be able to call them if needed?; 2) are you familiar with the phrase, “Drop, Cover, and Hold”? Also, we adapted it with some minor changes. We added “have learned first aid” to “have purchased first aid kit” statement. We added “and extra cloths and blankets” at the end of” put aside extra plastic bags and toilet paper for use as an emergency toilet” statement. We replaced “roof” with “my way” in “ensuring that the roof will probably not collapse in an earthquake. We added some examples to “take some steps at work” statement such as attending an earthquake preparedness class and having fire insurance. The content validity of the Persian checklist was tested by 10 experts. We calculated CVI and CVR equal to 0.92 and 0.95, respectively. Also, the face validity and reliability of this checklist were examined in a pilot study on 40 adults. According to their recommendations, minor revisions were made to increase the transparency and understandability of the statements. Likewise, the reliability of this checklist was measured by internal consistency (Chronbach α = 0.858). The total score of this checklist was ranging from 0 to 25 and the higher score reflects more preparedness.

The awareness on earthquake response questionnaire included seven questions with true/false answers (In an earthquake: you should get down close to the ground; you should get under a big piece of furniture such as a desk or other covers; you should hold on to a firm object until the end of the shaking; you should stand in a doorway; If you are indoors during an earthquake, you must exit the building; If you are in bed during an earthquake, you should stay there and cover your head with a pillow; next to pillars of buildings and interior wall corners are the safe areas). One point was given for each correct answer. Therefore, the total score of this domain was seven points.

The adapted questionnaire of earthquake preparedness based on the HBM was used. The original questionnaire has been established and validated by Inal et al. [ 1 ] in Turkey. The forward and backward translation method was used for translating the original questionnaire. According to the experts’ opinions, some minor changes were made to adapt the items of the questionnaire for the study population in the present study. Thereby, three questions were added to the questions of the cues to action (Radio and TV encourage me to prepare for disasters, I usually seek information about disaster preparedness from Radio and TV, and I usually obtain information about disaster preparedness from health providers). Besides, one question was added to the questions of perceived benefits (preparedness for disaster will reduce financial losses and injuries). Then, the content validity of the questionnaire was assessed by a panel of experts including 10 Health specialists in the field of health in disasters, health education, health promotion, and safety promotion (CVR = 0.92 & CVI = 0.85). Next, the face validity and reliability of the questionnaire were measured in a pilot study on 40 people over 18 years old. The reliability was calculated by using internal consistency. One question from the perceived severity (emergency and the experience of disasters does not change my life) and one question from self-efficacy (I cannot create an emergency plan with my neighbors) was excluded based on the results of Cronbach’s alpha. In Iran, neighbors don’t share their plans; therefore, it was logical to exclude these items. Finally, the questionnaire consisted of 33 questions, including perceived severity (2 questions, α = 0.709), perceived susceptibility (6 questions, α = 0.664), perceived benefits (4 questions, α = 0.758), perceived barriers (6 questions, α = 0.822), self-efficacy (7 questions, α = 0.677), cues to action (8 questions, α = 0.683), and total questions (33 questions, α = 0.809). All of the items were assessed by a 5-point Likert scale ranging from ‘completely disagree’ (one point) to ‘completely agree’ (5 points). Some items were scored reversely.

Statistical analysis

We used the analysis of variance (ANOVA) and independent t-test to determine the relationship between variables. Besides, the multivariate linear regression model was used to determine the predictors of household earthquake preparedness. The Stata 14.2 software was used to analyze the data.

In this study, 933 questionnaires were analyzed (response rate: 93.3%). The mean age of participants was 38.24 ± 12.85 years. Besides, 228 (24.44%) participants were male and 656 (70.31%) were female. About 80% of the participants did not have an academic education and had a diploma degree or less than a diploma degree. Also, 573 (61.41%) participants were homeowners (Table  1 ).

The earthquake preparedness of the participants was low. The household preparedness score was 7.5 out of 25. In other words, the average earthquake preparedness of households was approximately 30%. Besides, the self-efficacy score was 60.79 ± 0.55 and the score of cues to action was 66.57 ± 0.45 (Table  2 ).

The participants’ preparedness for the earthquake had a significant relationship with gender ( P  < 0.001), homeownership ( P  < 0.001), marital status ( P  < 0.001), and previous experience of a destructive earthquake ( P  < 0.001). Also, the mean score of earthquake preparedness was higher in those who reported moderate or good economic status. The mean difference was statistically significant by the Scheffe test ( P  < 0.001). Furthermore, the one-way ANOVA/Scheffe’s test showed that there was a significant difference between illiterate people and those who had either university education or diploma degree and similarly, a significant difference in earthquake preparedness was observed between primary education and those who had either academic education or diploma degree ( P  < 0.001) (Table  3 ).

The crude regression analysis showed that all constructs of the HBM except perceived severity were significant predictors of earthquake preparedness (P < 0.001) but after using stepwise regression, only perceived benefits ( P  < 0.006), cues to action ( P  < 0.001), and self-efficacy ( P  < 0.001), significantly predicted the earthquake preparedness (Table  4 ).

In this study, we determined the level of earthquake preparedness of households and its predictors based on HBM. The earthquake preparedness of the participants was low. The participants’ preparedness for the earthquake had a significant relationship with homeownership, education, and previous experience of a destructive earthquake. Also, perceived benefits, cues to action, and self-efficacy significantly predicted the earthquake preparedness.

Despite the strong emphasis on earthquake preparedness to prevent its damaging effects, the findings of this study showed that most people had low preparedness for earthquakes which is similar to the findings of previous studies [ 18 , 23 , 24 , 25 ]. This can be very dangerous in areas that are vulnerable to earthquakes. Earthquake preparedness is related to the previous experience of destructive earthquakes and their damaging consequences. Households that had previously experienced destructive earthquakes were more prepared than those who had not previously experienced this event, which is similar to previous finding [ 26 , 27 ]. People who live in earthquakes zones and understand the potential losses from earthquakes are more likely to be prepared in comparison to people living in other areas [ 18 ]. This could be due to recalling previous injuries as well as the fear of recurrence of similar injuries in future earthquakes. This goes back to the culture of societies that their members don’t believe that they are at risk of the occurrence of hazards and their consequences until they experience these hazards. Regarding the high frequency of earthquakes in the Hamadan province, most of the participants in this study had previous earthquake experience but they were not prepared for earthquakes. Perhaps this is because most of the recent earthquakes in Hamadan did not result in deaths and as a result, these households do not take the risk of earthquakes seriously and do not find it essential to hold earthquake preparedness [ 28 ].

Besides, education was significantly correlated with households’ earthquake preparedness, which is similar to the results of the studies by Russell et al. and Ghadiri & Nasabi [ 29 , 30 ]. One explanation can be that people with higher education are more knowledgeable, more aware of earthquakes danger, and more inclined to acquire new skills [ 28 , 31 ].

In this study, we found that the preparedness of participants has a significant relationship with homeownership. Two previous studies showed homeowners were more prepared for earthquakes than renters [ 32 , 33 ], whereas a study in Ethiopia in 2014 showed that homeownership had no relationship with disaster preparedness [ 28 ]. One of the explanations is that owners can make the necessary changes despite preparedness costs due to place attachment, but more studies are required to confirm the role of homeownership.

We adjusted for multiple possibly confounding factors in our analysis. After adjusting the model, perceived benefit, cues to action, and self-efficacy had significant predictors of earthquake preparedness. It is more possible that people’s earthquake preparedness increases when they are aware of the benefits of earthquake preparedness. Furthermore, people with high self-efficacy feel they can prepare for earthquakes [ 34 ]. On the other hand, people may find the earthquake hazardous but if they feel enough confident to reduce damages of earthquakes, they will engage in preparedness. If people perceive the benefits of a healthy behavior higher than the barriers of it, they will engage in that healthy behavior. Therefore, people may perceive earthquakes as a high threat but it can be expected that higher perceived benefits and self-efficacy among them result in higher preparedness. One possible explanation is that the perceived benefits motivate people to perform a specific behavior and adopt an action [ 10 ]. Besides, the significant association of self-efficacy with preparedness at the household level for earthquakes could be explained by the positive and strong association of cues to actions with earthquake preparedness at the household level. Self-efficacy can be improved by observational learning, role modeling, and encouragement. Self-efficacy affects one’s efforts to change risk behavior and causes the continuation of one’s safe behavior despite obstacles that may decrease motivation [ 10 ]. Moreover, cues to action associated with earthquake preparedness [ 1 ]. Cues to action mention to influences of the social environment such as family, friends, and mass media. Mass media can play a vital role in educating the public about earthquake preparedness.

This study has several limitations. Firstly, using a self-reporting approach for data gathering, and secondly, due to the low number of relevant studies on earthquake preparedness based on behavioral change models, it was less possible to compare different studies with the findings of this study. Third, it should be noted that the results of this study can be generalized in the study population and setting, but for other settings it should be done with caution. Despite these limitations, this study had some strengths, we use a theoretical framework for identifying factors that influence earthquake preparedness with a large sample size. Also, the findings of this study are useful for emergency service providers, health authorities, and policymakers in designing and implementing earthquake preparedness programs. This research is also useful for researchers as it can be used as a basis for future researches. It is recommended to design and implement interventions to improve household preparedness for an earthquake based on self-efficacy, perceived benefits, and cues to action.

Households’ earthquake preparedness was insufficient and low. Controlling the damaging consequences of earthquakes is related to the preparedness for earthquakes and can prevent its devastating effects. Perceived benefits, cues to action, and self-efficacy had a significant relationship with earthquake preparedness. The possibility of people being more prepared is increased when they are aware of and understand properly the benefits of being prepared for earthquakes and other disasters. People with high self-efficacy also feel more empowered for taking better care of themselves and their families during disasters. Cues to action would also encourage earthquake preparedness. Since health centers and TV and radio programs were the primary sources of learning about earthquakes for the people, it is recommended that broadcasting provides related programs and educates people about earthquake preparedness. The predictors that were assessed in this study can be taken into account for designing and implementing proper interventions in this field.

Availability of data and materials

The analyzed datasets during this study are available from the corresponding author on reasonable request.

Abbreviations

Health Belief Model

Confidence Interval

Analysis of Variance

Content Validity Ratio

Content Validity Index

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Acknowledgments

The authors gratefully thank all of the participants in this study.

This study was approved and financially supported by the Deputy of Research and Technology of Hamadan University of Medical Sciences (number: 9707174168). The funder of this study had no role in the study design, data collection, data analysis, data interpretation, or writing the manuscript.

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Masoumeh Rostami-Moez & Mohammad Rabiee-Yeganeh

Chronic Diseases (Home Care) Research Center and School of Nursing & Midwifery, Hamadan University of Medical Sciences, Hamadan, Iran

Mohammadreza Shokouhi

Department of Epidemiology, School of Health, Hamadan University of Medical Sciences, Hamadan, Iran

Amin Dosti-Irani

Department of Public Health, School of Public Health, Hamadan University of Medical Sciences, Shahid Fahmideh Ave, Hamadan, Iran

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Social Determinants of Health Research Center, Hamadan University of Medical Sciences, Hamadan, Iran

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MRM has made substantial contributions to the conception and design of the study, took responsibility for and coordinated the acquisition of data and contributed actively in the analysis of the data and the writing of the manuscript. FRS has made substantial contributions to the conception and design of the study, interpretation of the data, and writing up the manuscript. MS contributed to the design of the study and preparation of the manuscript. MRY was involved in the design of the study and the data gathering process. ADI contributed to the study design, data analysis, and interpretation. All authors read and approved the final manuscript.

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Rostami-Moez, M., Rabiee-Yeganeh, M., Shokouhi, M. et al. Earthquake preparedness of households and its predictors based on health belief model. BMC Public Health 20 , 646 (2020). https://doi.org/10.1186/s12889-020-08814-2

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Earthquakes: What are they and how do they occur?

Earthquakes are one of Earth's biggest and deadliest natural disasters.

What causes earthquakes?

• Detection and measurements

Biggest earthquake

Benefits of earthquakes.

• Earthquakes on other planets?

Additional resources

Spawning below Earth's surface and carrying immense energy, earthquakes can strike without warning. It therefore comes as no surprise that they are one of our planet's deadliest natural disasters. 

Earthquakes occur when vast amounts of energy are released from Earth 's crust in the form of seismic waves. The waves radiate outwards from the source of the stress, known as the hypocenter, and can cause untold damage to infrastructure when they reach the surface. 

Approximately 20,000 earthquakes occur every year, which equates to around 55 every single day according to the United States Geological Survey (USGS). Fortunately for us, the majority of these go completely unnoticed and are too weak to cause any damage. 

Related: Haiti's earthquake aftermath is visible from space  

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Scientists anticipate approximately 16 major earthquakes (categorized as magnitude 7 and above) per year, after studying long-term records from about 1900. According to USGS, in the last 40 to 50 years we have exceeded this number approximately 12 times, and in 2010 alone we experienced 23 major earthquakes. 

But that's about as far as our earthquake prediction capabilities go, as these seismic beasts are virtually impossible to predict and entirely unpreventable. Instead of investing time and energy into futile preventative measures. Humans have learned that preparedness and appropriate infrastructure are key. As the famous saying goes "earthquakes don't kill people, buildings do."

Many areas that are prone to earthquakes have adopted rigorous building codes to help ensure that new buildings or adjustments to old ones are done with earthquake resistance in mind. There are myriad examples of building improvements, from rubber shock absorbers in the foundations to help absorb tremors to special steel frames designed to sway without affecting the structural integrity of the building. 

Remarkably, large skyscrapers can also be constructed to withstand considerable ground shaking. Some are built containing large stabilizing balls known as "dampers" which essentially act as giant pendulums, moving back and forth to counter any movement of the building itself. These dampers help stabilize the building during high winds, or seismic activity. You can see one of these dampers for yourself from the observation deck in the famous Taipei 101 building in Taiwan .  

Earthquakes are triggered by a variety of processes including volcanic eruptions, landslides and even meteor strikes. But the most common cause of earthquakes lies deep below our feet in the form of plate tectonics.

Sandwiched between the atmosphere above and the asthenosphere below (the upper layer of the earth's mantle) lies the outermost layer of Earth — the lithosphere . This layer consists of numerous pieces, or plates, that jostle around on top of the asthenosphere like an energetic jigsaw puzzle. Temperatures in the asthenosphere range from 2,370 degrees Fahrenheit to 3,090 degrees Fahrenheit (1,300 degrees Celsius to 1,700 degrees Celsius) and the depth ranges from 62 miles to 155 miles (100 km to 250 km) below Earth's surface. The high temperatures result in the asthenosphere layer having enough elasticity to "flow" — despite being solid —  according to the educational website Study.com . This ductile layer can flow slowly under heat convection and help move magma and rocks through Earth, contributing to the movement of tectonic plates. 

When two plates attempt to move past each other, friction prevents them from gliding on by with relative ease, causing stress to build up at the point of contact. Though their movement is hindered, the plates never stop moving, so ultimately something has to give. 

Eventually, the rock slips, releasing vast amounts of energy in waves that travel through Earth's interior to the surface and generate the shaking we perceive during an earthquake. The point on Earth's surface that lies directly above the focus — or hypocenter — of the earthquake is known as the epicenter. 

Earthquakes can arise anywhere between Earth's surface and around 700 kilometers deep according to a statement from USGS . They're prevalent along the edges of plate boundaries and according to the British Geological Survey , over 80% occur around the edge of the Pacific Ocean, in an area known as the "Ring of Fire." Some earthquakes, however, can appear far from boundaries, right in the middle of the plate. These are known as intraplate quakes and although little is known about them, some scientists believe that they result from preexisting faults that formed within Earth's crust long ago.  

How are earthquakes detected and measured?

The branch of science relating to the study of earthquakes and related events is known as seismology. 

A seismograph or seismometer is an instrument used to detect and measure ground movements caused by seismic activity. A seismogram is the record of ground movements , according to the British Geological Survey. A simple seismometer consists of a pen attached to a suspended mass which — when the ground moves — will move due to its inertia and record the movements on a rotating drum of paper. More sophisticated seismometers record the motion of the ground in three dimensions: up and down, east to west and north to south. 

Scientists use this data to calculate the size of the earthquake, known as magnitude. 

The Richter scale is perhaps the most well-known way of measuring an earthquake's magnitude. Developed in 1935 by Charles F. Richter, this logarithmic scale was designed to compare the size of earthquakes in the California region.

The Richter scale goes from 1 to 10, whereby one increase in the scale accounts for a 10-fold increase in magnitude. The magnitude of the earthquake relates to the amplitude (distance from the center line to the top of the crest or bottom of a trough of a wave) of the waves recorded by the seismograph. 

One problem with this technique is that earthquake wave amplitudes are not only affected by the earthquake itself, but also by the distance between the seismometer and the epicenter and even the type of rock the waves are traveling through. As such, various adjustments need to be made to seismometer data to account for the variations in conditions, so that the calculated magnitude is the same regardless of where it was measured. 

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As more and more seismometers were installed around the world, it became incredibly difficult to adjust the data to make it "fit" with the Richter scale as it became apparent that the scale only worked for certain frequency and distance ranges , according to the USGS. 

Scientists, therefore, came up with a new scale that can be used all over the world called moment magnitude. The moment refers to the amount of energy released at the time of slip on the fault multiplied by the area of the fault surface affected. It can be estimated using seismometers and is related to the total energy released in the earthquake. Moment magnitude is the most reliable estimate of earthquake size. 

The effect of an earthquake on Earth's surface — the intensity — is evaluated with the Modified Mercalli (MM) Intensity Scale . The scale is rather ambiguous, as it is not based on numerical values but instead assigns a ranking based on observable effects. This could be misleading as two earthquakes of the same magnitude striking two areas with different levels of earthquake preparedness or of different geological compositions will result in the assignment of very different intensity rankings. 

The biggest earthquake ever recorded was in 1960 when a magnitude 9.5 quake struck Chile. Named the Valdivia earthquake after the city most affected by the quake, it left 2 million people without homes, injured at least 3,000 and killed around 1,655 according to National Geographic . 

It might be surprising to hear that earthquakes can be beneficial, but they can actually tell us a lot about Earth's interior, including where different geological layers are located. 

When seismometers around the world detect seismic waves, they record their velocities, which tell scientists a great deal about the composition, temperature and pressure of the material through which the waves have traveled. 

The location and magnitude of an earthquake can also provide a window into the Earth's tectonic processes at work. Increased tectonic knowledge helps scientists improve their calculations of the probability of seismic events along particular faults, according to the Woods Hole Oceanographic Institution .  

Do earthquakes happen on other planets?

At present, we do not know of any other planet that possesses a lithosphere divided into true plates that undergo tectonic processes, according to the Lunar and Planetary Institute . That being said, that isn't to say that quakes don't exist elsewhere in the solar system , for there is more than one way to trigger a seismic event. 

Moonquakes and marsquakes have both been detected, allowing researchers to probe further into the interiors of these distant worlds. 

According to Horizon magazine, moonquakes are caused by: 

• Meteoroids hitting the lunar surface 
• Earth's gravitational pull stretching and squeezing the moon 's interior.
• Buckles and breaks from the lunar crust as a result of the moon cooling down. 
• Heating from the sun triggering thermal quakes 

The first seismometer on the moon was actually placed there during Apollo 11 and was even put to the test by Buzz Aldrin stamping his foot nearby (the instrument recorded it), according to the EU Research and Innovation Magazine, Horizon . Several other seismometers were deployed on subsequent Apollo missions and collected valuable seismic data. 

The seismometers were operational until 1977. Data collected from the instruments is still being analyzed by scientists as there are currently no active lunar seismometers. 

Scientists are hopeful that future missions to the moon under the Artemis program will see more sophisticated seismometers deployed on the lunar surface so we can peer even further into its interior. 

Turning our attention to the Red Planet, we had to wait a little longer to witness seismic activity on Mars . The first marsquake was detected by NASA's InSight Mars Lander on Apr. 6, 2019, with its Seismic Experiment for Interior Structure (SEIS) instrument. Since then, over 1,300 marsquakes have been detected by the lander, including a magnitude 5 on May. 4, 2022 — the strongest tremor ever detected on a planet besides Earth. 

To learn more about what to do in the event of an earthquake the U.S. government has some dedicated resources designed to help you stay safe. If you want to know more about the latest seismic events check out this interactive map from USGS detailing the latest earthquakes around the world. Read about how NASA's Jet Propulsion Laboratory is using satellite data to help map earthquake damage so we can learn more about these seismic events.

Follow us on Twitter @Spacedotcom and Facebook . 

Bibliography

Determining the depth of an earthquake. Determining the Depth of an Earthquake | U.S. Geological Survey. Retrieved October 13, 2022, from https://www.usgs.gov/programs/earthquake-hazards/determining-depth-earthquake

Earthquake facts & earthquake fantasy. Earthquake Facts & Earthquake Fantasy | U.S. Geological Survey Retrieved October 13, 2022, from https://www.usgs.gov/programs/earthquake-hazards/earthquake-facts-earthquake-fantasy

Earthquake glossary. U.S. Geological Survey. Retrieved October 13, 2022, from https://earthquake.usgs.gov/learn/glossary/?term=richter+scale

Earthquakes. National Geographic Society. Retrieved October 13, 2022, from https://education.nationalgeographic.org/resource/earthquakes

Earthquakes. Woods Hole Oceanographic Institution. Retrieved October 13, 2022, from https://www.whoi.edu/know-your-ocean/ocean-topics/ocean-human-lives/natural-disasters/earthquakes/

How are earthquakes detected, located and measured? British Geological Survey. Retrieved October 13, 2022, from https://www.bgs.ac.uk/discovering-geology/earth-hazards/earthquakes/how-are-earthquakes-detected

Keesey, L. (April 29, 2020). NASA scientists to make seismometer system to measure Moonquakes. NASA. Retrieved October 13, 2022, from https://www.nasa.gov/feature/goddard/2020/nasa-scientists-tapped-to-mature-more-rugged-seismometer-system-to-measure-moonquakes

May 22, 1960 CE: Valdivia earthquake strikes Chile. National Geographic Society. Retrieved October 13, 2022, from https://education.nationalgeographic.org/resource/valdivia-earthquake-strikes-chile

The modified Mercalli intensity scale. U.S. Geological Survey. Retrieved October 13, 2022, from https://www.usgs.gov/programs/earthquake-hazards/modified-mercalli-intensity-scale

Moment magnitude, richter scale - what are the different magnitude scales, and why are there so many? U.S. Geological Survey. Retrieved October 13, 2022, from https://www.usgs.gov/faqs/moment-magnitude-richter-scale-what-are-different-magnitude-scales-and-why-are-there-so-many

O'Callaghan, J. (August 10, 2020). Moonquakes and Marsquakes: How we peer inside other worlds. Horizon Magazine. Retrieved October 13, 2022, from https://ec.europa.eu/research-and-innovation/en/horizon-magazine/moonquakes-and-marsquakes-how-we-peer-inside-other-worlds

Shaping the planets: Tectonism. Lunar and Planetary Institute (LPI). Retrieved October 13, 2022, from https://www.lpi.usra.edu/education/explore/shaping_the_planets/tectonism/

What is the asthenosphere? Study.com. Retrieved October 18, 2022 from https://study.com/learn/lesson/asthenosphere-temperature-facts-density.html

What keeps the continents floating on a sea of molten rock? Surprising questions with surprising answers. West Texas A&M University. Retrieved October 18, 2022, from https://www.wtamu.edu/~cbaird/sq/2013/07/18/what-keeps-the-continents-floating-on-a-sea-of-molten-rock

Where do earthquakes occur? British Geological Survey. Retrieved October 13, 2022, from https://www.bgs.ac.uk/discovering-geology/earth-hazards/earthquakes/where-do-earthquakes-occur/

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What Is an Earthquake?

An earthquake is an intense shaking of Earth’s surface. The shaking is caused by movements in Earth’s outermost layer.

Why Do Earthquakes Happen?

Although the Earth looks like a pretty solid place from the surface, it’s actually extremely active just below the surface. The Earth is made of four basic layers : a solid crust, a hot, nearly solid mantle, a liquid outer core and a solid inner core.

A diagram of Earth's layers. Earthquakes are caused by shifts in the outer layers of Earth—a region called the lithosphere.

The solid crust and top, stiff layer of the mantle make up a region called the lithosphere . The lithosphere isn’t a continuous piece that wraps around the whole Earth like an eggshell. It’s actually made up of giant puzzle pieces called tectonic plates . Tectonic plates are constantly shifting as they drift around on the viscous , or slowly flowing, mantle layer below.

Earth's crust is fractured into tectonic plates that have been moving very slowly over the Earth's surface for millions of years. Credit: USGS

This non-stop movement causes stress on Earth’s crust. When the stresses get too large, it leads to cracks called faults . When tectonic plates move, it also causes movements at the faults. An earthquake is the sudden movement of Earth’s crust at a fault line.

This photograph shows the San Andreas Fault, a 750-mile-long fault in California. Credit: Public Domain

The location where an earthquake begins is called the epicenter . An earthquake’s most intense shaking is often felt near the epicenter. However, the vibrations from an earthquake can still be felt and detected hundreds, or even thousands of miles away from the epicenter.

How Do We Measure Earthquakes?

The energy from an earthquake travels through Earth in vibrations called seismic waves . Scientists can measure these seismic waves on instruments called seismometer. A seismometer detects seismic waves below the instrument and records them as a series of zig-zags.

Scientists can determine the time, location and intensity of an earthquake from the information recorded by a seismometer. This record also provides information about the rocks the seismic waves traveled through.

A seismometer records seismic waves as a series of zig-zags. Credit: Wikimedia Commons user Z22, CC BY-SA 3.0

Do Earthquakes Only Happen on Earth?

Earthquake is a name for seismic activity on Earth, but Earth isn’t the only place with seismic activity. Scientists have measured quakes on Earth's Moon, and see evidence for seismic activity on Mars, Venus and several moons of Jupiter, too!

NASA’s InSight mission took a seismometer to Mars to study seismic activity there, known as marsquakes. On Earth, we know that different materials vibrate in different ways. By studying the vibrations from marsquakes, scientists hope to figure out what materials are found on the inside of Mars.

An artist's illustration of the Mars InSight lander operating on the surface of Mars. Credit: NASA-JPL/Caltech

InSight is collecting tons of information about what Mars is like under the surface. These new discoveries will help us understand more about how planets like Mars—and our home, Earth—came to be.

More to Explore!

Make a Fan With Earth's Layers!

Plate Tectonics

All About Mars!

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NOTIFICATIONS

Investigating earthquakes – question bank.

• + Create new collection

An inquiry approach is a method often used in science education. This question bank provides a list of questions about earthquakes and places where their answers can be found.

The questions are in three groups:

Earthquakes in general

Base isolation.

The article Investigating earthquakes – introduction has links to further resources and student activities.

This question bank asks general questions about earthquakes.

Q. We can't see through solid rock, so where's the evidence for how earthquakes work?

• Inside the Earth
• Plate tectonics
• Moulding the Earth

Q. Why does the earth shake so far away from where an earthquake starts?

Q. can i see earthquake waves.

• Seismic waves

Q. Who is talking about this?

• Keith Machin

Q. What are New Zealand scientists doing about this?

• The Alpine Fault
• Squishy rocks and earthquakes
• Seismic engineering at Canterbury University

Q. How long have we known about this?

• Earthquakes – timeline

This question bank focuses on the form of earthquakes known as slow slips.

Q. How can slow slips help us understand earthquakes?

• What are slow slips?
• Dr Laura Wallace

Q. Where can we find out about this?

• GNS Science Limited

A group of questions focuses on the technology of base isolation.

Q. How do I know which buildings are the safest?

• Strengthening Parliament House
• Seismic engineering

Q. How can base isolators be tested without being in an earthquake?

• How do base isolators work?
• Dr Bill Robinson
• Robinson Seismic Limited

See our newsletters here .

Would you like to take a short survey?

This survey will open in a new tab and you can fill it out after your visit to the site.

• Mission Statement

100 Frequently Asked Questions About Earthquakes and Their Answers

Q: What causes earthquakes?

A: It takes a very specific geological event to create an earthquake. Here’s how it happens: The ever-present movement of the tectonic plates beneath the Earth’s crust causes occasional collisions that release energy, essentially a grinding between two plates. This results in an earthquake. Most quakes tend to occur along fault lines (boundaries between plates) because this is where most movement occurs, plate-to-plate.

Q: What is an earthquake?

A: The United States Geological Survey defines an earthquake as such: “Earthquake is a term used to describe both sudden slip on a fault, and the resulting ground shaking and radiated seismic energy caused by the slip, or by volcanic or magmatic activity, or other sudden stress changes in the earth.” Simply stated, this type of disaster involves the events underneath the surface of the Earth that lead up to the quake and the actual quake itself.

Q: How do earthquakes happen?

A: Like most natural disasters, quakes require certain environmental circumstances to be in place for them to occur. Again quoting the United States Geological Survey, “An earthquake is caused by a sudden slip on a fault. The tectonic plates are always slowly moving, but they get stuck at their edges due to friction. When the stress on the edge overcomes the friction, there is an earthquake that releases energy in waves that travel through the Earth’s crust and cause the shaking that we feel.”

Q: What to do in an earthquake?

A: There is a very simple bit of advice to remember if you find yourself caught in a quake. This is from the Centers for Disease Control and Prevention, which published findings on the safest way to survive a quake. “DROP down onto your hands and knees before the earthquake knocks you down. This position protects you from falling but allows you to still move if necessary. COVER your head and neck (and your entire body if possible) underneath a sturdy table or desk. If there is no shelter nearby, get down near an interior wall or next to low-lying furniture that won’t fall on you, and cover your head and neck with your arms and hands. HOLD ON to your shelter (or to your head and neck) until the shaking stops. Be prepared to move with your shelter if the shaking shifts it around.”

Q: Where do earthquakes occur?

A: Quakes can occur just about anywhere. In fact, almost every state in the United States has recorded incidences of earthquakes occurring. However, some states and regions are more prone to such disasters than others. The ten states in the U.S. that receive the most earthquakes are:

• Washington State

Q: Why do earthquakes happen?

A: Earthquakes occur as a natural, though disastrous phenomenon. They are caused by a sudden slip, below the Earth’s surface, along a fault line. A fault line is a place where two tectonic plates meet. These plates are slowly moving, and sometimes they grind along each other, causing a shift of rock and a resulting quake to occur.

Q: How are earthquakes measured?

A: The Richter Scale is a special measurement designation used to determine the intensity and severity of an earthquake. According to the USGS, “Earthquakes are recorded by a seismographic network. Each seismic station in the network measures the movement of the ground at that site. The slip of one block of rock over another in an earthquake releases energy that makes the ground vibrate. That vibration pushes the adjoining piece of ground and causes it to vibrate, and thus the energy travels out from the earthquake hypocenter in a wave.” Earthquakes are measured by their magnitude on a scale of 0 to, essentially, infinity. The highest magnitude earthquake ever recorded ranked at 9.5 on the Richter Scale.

Q: How long do earthquakes last?

A: Most small earthquakes only last for a few seconds, but more intense earthquakes can last for several minutes. A quake rarely lasts longer than a few minutes. However, such events can cause massive, even catastrophic devastation in those minutes.

Q: How to prepare for an earthquake?

A: It’s not easy to prepare for a quake because such events are not easy to predict. Ready.gov, a government-funded and run disaster preparedness website, says this about preparing for such an event: “Practice drop, cover, and hold on with family and coworkers. Create a family emergency communications plan that has an out-of-state contact. Put together a stash of non-perishable foods, cleaning supplies, and water for several days, in case services are cut off in your area. Secure heavy items in your home like bookcases, refrigerators, televisions and objects that hang on walls. Store heavy and breakable objects on low shelves.”

Q: Where are earthquakes common?

A: In the United States, the most commonplace for quakes to occur is in California. This is because two tectonic plates meet in California, the Pacific Plate, and the North American Plate. The major fault line that is formed by the plates is called the San Andreas Fault. It’s important to keep in mind that, though earthquakes tend to occur in specific regions where tectonic plates meet, quakes can occur at any location and at any time. For example, only eight states in the U.S. have not recorded a quake event (at least not between 1973 and 2003). These are Wisconsin, Vermont, North Dakota, Maryland, Iowa, Florida, Delaware, and Connecticut. As for the remaining 42 states, frequency of quake events ranges anywhere from West Virginia, which has just one quake on record, to Alaska, which has 12,053 earthquakes on record for the 1973 to 2003 recording period.

Q: What is the epicenter of an earthquake?

A: The “epicenter” (as one would normally think of it) in an earthquake is not called that, though such a term does have its place in quake nomenclature. According to the United States Geological Survey, “An earthquake is what happens when two blocks of the Earth suddenly slip past one another. The surface where they slip is called the fault or fault plane. The location below the Earth’s surface where the earthquake starts is called the hypocenter, and the location directly above it on the surface of the Earth is called the epicenter.”

Q: Can earthquakes be predicted?

A: One of the most common natural disasters to occur on Earth, earthquakes can happen almost anywhere, at any time. They are highly unpredictable, as there is no “season” for quakes like there is for many other natural disasters. Quake tremors can occur at any time of the year and at any time of the day or night. They can occur under any weather conditions. They cannot be predicted, at least not more so than a few minutes out from the first tremor. Given how common earthquakes are and their potential for being particularly devastating to established urban areas, it’s important to prepare for them and to know how to respond when one occurs.

Q: Does fracking cause earthquakes?

A: Possibly, yes. Fracking intentionally causes small quakes, and this process has been linked to larger quakes. A magnitude four quake in Texas some years ago was linked to nearby fracking. Also, detonating a nuclear warhead is another human-created cause of quakes. Detonating such an immense payload causes a seismic shift that is so immense it is comparable to an earthquake. Quoting Michigan Technological University, “The largest underground explosions, from tests of nuclear warheads (bombs), can create seismic waves very much like large earthquakes. This fact has been exploited as a means to enforce the global nuclear test ban, because no nuclear warhead can be detonated on Earth without producing such seismic waves.”

Q: What was the biggest earthquake?

A: While large earthquakes are relatively common in the United States, early warning systems implemented by the United States Geological Survey provide alerts to help Americans take shelter. Furthermore, more durable building methods and well-established emergency response systems help save lives and reduce fatalities during U.S.-based quakes. This is why relatively few Americans die in quakes, compared to other countries that experience similar-magnitude quakes. The most powerful earthquake to strike the United States occurred in Alaska in 1964. This quake was a magnitude 9.2 that struck Prince William Sound and killed 139 people.

Q: Are earthquakes increasing?

A: The million-dollar question, are quakes increasing in intensity and frequency? In the paper, geophysicist Paul Lundgren of NASA’s Jet Propulsion Laboratory in Pasadena, California, said, “We’ve seen that relatively small stress changes due to climate-like forcings can effect microseismicity. A lot of small fractures in Earth’s crust are unstable. We see also that tides can cause faint Earth tremors, known as microseisms. But the real problem is taking our knowledge of microseismicity and scaling it up to apply it to a big quake, or a quake of any size that people could feel, really. Climate-related stress changes might or might not promote an earthquake to occur, but we have no way of knowing by how much.” The short answer is that scientists simply do not know if earthquakes will get worse or not. Regardless, individuals and families need to understand how to prepare for an earthquake and what to do should one occur.

Q: What is the main cause of an earthquake?

A: The main cause is a shifting of tectonic plates that create a sudden movement of stone beneath the Earth’s surface.

Q: What to do after an earthquake?

A: What you do after a quake depends on where you are and the type of environment/risks you have around you. According to the City of Portland’s official warning system on quakes, “Evacuate if you are in a tsunami hazard zone. Walk inland or to higher ground as soon as it is safe to do so. Do not wait for official notification. Stay away from the coast until officials permit you to return. Check for injuries. Do not move seriously-injured persons unless they are in immediate danger. Check for hazards such as fires, gas leaks, downed utility lines and fallen objects. Clean up any potentially harmful materials spills. Expect aftershocks. Aftershocks following large earthquakes can be large and damaging.”

Q: Can you predict earthquakes?

A: Most scientists maintain that quake prediction is inherently impossible, though some argue that advances in technology could lead to the effective and reliable prediction of earthquakes.

Q: How many earthquakes happen a day?

A: The National Earthquake Information Center locates about 20,000 quakes across the plant each year, or 55 quakes per day.

Q: How often do earthquakes occur?

A: Approximately 55 significant, notable earthquakes occur on planet Earth each day, but the location of those quakes vary, region to region. For example, California, a quake-prone state in the U.S., experiences about 100 micro-quakes every day. Compare that to other states in the U.S. that may only experience a quake once every several years.

Q: How to survive an earthquake?

A: Many organizations provide advice on quakes. The agreed-upon rule of thumb is best put by the CDC: “DROP down onto your hands and knees before the earthquake knocks you down. This position protects you from falling but allows you to still move if necessary. COVER your head and neck (and your entire body if possible) underneath a sturdy table or desk. If there is no shelter nearby, get down near an interior wall or next to low-lying furniture that won’t fall on you, and cover your head and neck with your arms and hands. HOLD ON to your shelter (or to your head and neck) until the shaking stops. Be prepared to move with your shelter if the shaking shifts it around.”

Q: What happens during an earthquake?

A: Earthquakes are unique in that they are a literal shaking of the Earth beneath our feet. Earthquakes are vibrations coming up through the Earth’s crust that cause shaking on the surface. Sometimes the shaking feels like it is going back and forth. Sometimes it is entirely erratic and without a pattern.

Q: What is the largest earthquake ever recorded?

A: While the 1964 Great Alaska Earthquake was the worst U.S.-based quake, it was only the second-worst earthquake ever recorded internationally. The worst quake ever recorded was in Bi-Bio Chile. It was a 9.5 magnitude quake, whereas the Alaska quake was a 9.2. The Chile quake occurred in 1960.

Q: What plate boundary causes earthquakes?

A: According to Brooklyn College, the key is in the convergent plate boundaries. According to the college’s report: “At convergent plate boundaries, where two continental plates collide earthquakes are deep and also very powerful. In general, the deepest and the most powerful earthquakes occur at plate collision (or subduction) zones at convergent plate boundaries.”

Q: Where are earthquakes most likely to occur?

A: Quakes are most likely to occur where two plate boundaries meet. On Planet Earth, that includes places primarily along the rim of the Pacific Ocean, including states and countries along the western Americas, plus China, Japan, Russia, North and South Korea, and various islands along the fringes of the Pacific Ocean.

Q: Can dogs sense earthquakes?

A: While there is no scientific consensus that either confirms or denies it, some believe that dogs possess such sensitive hearing that they can pick up the faint scraping and grinding of rocks beneath the surface of the Earth that precede an earthquake.

Q: Can scientists predict earthquakes?

A: Seismographs begin alarming us of an earthquake just a few seconds before the actual tremors set in, which is all the warning we usually have before a quake occurs.

Q: What does an earthquake feel like?

Q: Can earthquakes cause tsunamis?

A: Absolutely. In 1960, the largest earthquake ever recorded hit Chile. This magnitude 9.5 quakes caused 1,600 deaths in Chile. Though the earthquake did not occur anywhere near the United States, the earthquake caused a tsunami that traveled across the Pacific Ocean and hit Hawai’i. Thirty-five-foot waves crashed on the island of Hilo and killed 61 people.

Q: What do earthquake waves have in common with other waves?

A: Like many other types of waves, quake waves bend when they pass through different materials, which is part of why quake tremors and the direction they travel are so unpredictable.

Q: What is a fault earthquake?

A: A fault refers to the fracture along the blocks of crust on either side of two tectonic plate boundaries. A fault line is where most quakes occur.

Q: What measures earthquakes?

Q: Where to go during an earthquake?

A: Earthquakes can happen at any time and with very little warning. Experts recommend that if you’re already inside when an earthquake strikes, stay inside. Do not run outside or to other rooms during an earthquake. Staying put and seeking cover offers the best chance at avoiding injury. Don’t stand in a doorway or near a window. Seek shelter underneath something sturdy, such as a table. If you have children or elderly relatives living with you, help them seek refuge first. Earthquake tremors are usually short-lived. Seek shelter and cover and wait it out.

Q: How many aftershocks are normal after an earthquake?

A: Aftershocks are complicated. Small, unnoticeable aftershocks can occur for days, months, even years after a major earthquake. But most serious earthquakes produce just a handful of aftershocks that come about shortly after the main tremors recede.

Q: What is earthquake weather?

A: There is no such thing as earthquake weather. It is a myth.

Q: What is earthquake scale?

A: Earthquakes are measured on the Richter scale, a numerical scale used to express the magnitude of a quake. A destructive quake typically has a magnitude of 5.5 to 8.9, with quakes above 8.9 being quite rare and particularly destructive.

Q: What is true of both earthquakes and volcanos?

A: Earthquakes and volcanos are both caused by the movement of tectonic plates.

Q: What state has the most earthquakes?

A: California by far, with Alaska in second place.

Q: Where do the deepest earthquakes occur?

A: According to the United States Geological Survey, “The deepest earthquakes occur within the core of subducting slabs – oceanic plates that descend into the Earth’s mantle from convergent plate boundaries, where a dense oceanic plate collides with a less dense continental plate and the former sinks beneath the latter.”

Q: Who studies earthquakes?

A: Seismologists are Earth scientists who specialize in geophysics. They study the genus and propagation of the seismic waves that create earthquakes.

Q: Do transform boundaries cause earthquakes?

A: Yes. A transform plate boundary is simply a type of plate boundary where plates slide horizontally past each other. As the plates rub against each other, huge stresses on the rocks can cause portions of the rock to break, resulting in quakes.

Q: Do volcanoes cause earthquakes?

A: Yes, a volcanic eruption can indeed cause an earthquake, though volcano-caused quakes are usually not as intense as quakes caused by movement along tectonic plate boundaries.

Q: How do tectonic plates cause earthquakes?

A: From the USGS, “An earthquake is caused by a sudden slip on a fault. The tectonic plates are always slowly moving, but they get stuck at their edges due to friction. When the stress on the edge overcomes the friction, there is an earthquake that releases energy in waves that travel through the Earth’s crust and cause the shaking that we feel.”

Q: How many seismographs are needed to locate an earthquake?

A: Three seismographs are needed to locate a quake.

Q: What are the effects of earthquake?

A: Earthquakes are arguably one of the most destructive natural disasters, often because of the other disasters that they can cause. Earthquakes can trigger landslides and mudslides along hilly terrain, especially in areas with water-soaked soils. Earthquakes can also cause buildings to collapse, disrupting gas, electricity, and telephone service. Earthquakes can also cause fires and even tsunami waves.

Q: What does an earthquake sound like?

A: Low-pitched rumbles, rattling windows, car alarms, small trembles, crumbling concrete, and a shaking, shifting sound are the noises generally associated with earthquakes.

Q: What is the definition of earthquake?

A: A quake or tremor that results in a sudden and violent shaking of the ground is the key defining factor of an earthquake.

Q: What is the highest magnitude of earthquake?

A: The highest magnitude is essentially infinite in terms of potential quakes. However, since recording began, the highest magnitude that has occurred was a 9.5 magnitude quake in Chile that occurred in 1960.

Q: What to do if there is an earthquake?

A: When an earthquake occurs, stop, drop, cover, and hold on. This is the immediate response one should take to a quake because one usually does not have much time to prepare for such a disaster.

Q: What was the worst earthquake in history?

A: In this question, “worst” refers to the quake with the highest death toll, even if it was not the highest magnitude quake. According to Our World in Data, the deadliest earthquake ever recorded took place in Shaanxi, China, in 1556. It’s estimated to have killed about 830,000 people.

Q: Can earthquake happen anywhere?

A: Technically, Yes. However, earthquakes are far more common and likely in some regions than others.

Q: Has there ever been a 10.0 earthquake?

A: Not one that seismographs have recorded, but it is almost certain that one has occurred in world history.

Q: How do geologists locate the epicenter of an earthquake?

A: Geologists use the seismic waves created by an earthquake to measure the quake’s epicenter. The epicenter is located by measuring the difference between the arrival time of different types of waves.

Q: How long can an earthquake last?

A: Most disasters of this nature last just a few seconds. However, that does not mean one can come out of cover after the initial tremors recede, as aftershocks are quite common in earthquakes. Should a quake strike, one should not come out of the shelter until local responders and authorities say it is safe to do so, unless they live in a tsunamis-risk zone.

Q: What is considered a big earthquake?

A: Michigan Technological University published an excellent classification system of different magnitude earthquakes. According to their data, a quake event that measures a 5.5 magnitude or higher can cause significant damage.

Q: What magnitude earthquake can you feel?

A: You can feel anything above a 2.5 magnitude quake, but such quake events usually only cause minor damage.

Q: What is the best action to take during an earthquake?

A: Seek cover! Drop down low to the ground and try to take cover underneath a stable surface.

Q: How far away can you feel an earthquake?

A: A magnitude 4.0 quake can be felt as far as 60 miles away from the epicenter. A magnitude 5.5 quake can be felt 300 miles away from the epicenter. The higher the magnitude of the quake, the further away its tremors can be felt.

Q: How fast do earthquakes travel?

A: Quake tremors travel very fast. The rupture speed of the average tremor is 5,600 to 6,700 miles per hour. For context, most bullets only travel at about 1,700 miles per hour.

Q: What is an earthquake aftershock?

A: The United States Geological Survey defines aftershocks as such: “Aftershocks are smaller earthquakes that occur in the same general area during the days to years following a larger event or “mainshock.” They occur within 1-2 fault lengths away and during the period of time before the background seismicity level has resumed. As a general rule, aftershocks represent minor readjustments along the portion of a fault that slipped at the time of the mainshock. The frequency of these aftershocks decreases with time. Historically, deep earthquakes (>30 km) are much less likely to be followed by aftershocks than shallow earthquakes.”

Q: What not to do doing an earthquake?

A: There are some simple rules to follow during a quake regarding what not to do. For example, do not run outside or to other rooms during quake tremors. Avoid areas of a building that are right next to exterior walls. Windows, facades, and architectural details are often the first parts of the building to collapse.

Q: When is earthquake season?

A: There is no such thing as quake season. Statistically speaking, there is an equal distribution of quakes throughout the year and in all types of weather.

Q: Which floor is safest during an earthquake?

A: If a building collapses during a quake, no floor is a safe floor. However, being on a higher floor increases the chances of survival during such an event. Conversely, being lower to the ground makes evacuation easier after the quake. Simply stated, it’s more important to seek cover and protect oneself on whatever floor they are on during a quake than to go looking for a safer floor.

Q: Can animals predict earthquakes?

A: Some animals might be able to sense the initial tremors that come right before a quake occurs. While some scientific papers have been published, the research is still inconclusive and is awaiting peer review.

Q: Should you go outside during an earthquake?

A: No. If you are inside during a quake, stay inside. Don’t run outside during a quake. Don’t run at all during a quake. You are much safer by staying inside and seeking shelter underneath a table.

Q: What are earthquake waves called?

A: Such waves are usually called “Seismic Waves.”

Q: Where to hide during an earthquake?

A: The best place to seek shelter during a quake is in the center of a room under a sturdy desk or table, not near windows or exterior walls.

Q: Why are earthquakes dangerous?

A: According to National Geographic, “A powerful earthquake can cause landslides, tsunamis, flooding, and other catastrophic events. Most damage and deaths happen in populated areas. That’s because the shaking can cause windows to break, structures to collapse, fire, and other dangers. Geologists cannot predict earthquakes.”

Q: Why does the Earth shake when there is an earthquake?

A: Earthquakes are unique in that they are a literal shaking of the Earth beneath our feet. Earthquakes are vibrations coming up through the Earth’s crust that cause shaking on the surface. Sometimes the shaking feels like it is going back and forth. Sometimes it is entirely erratic and without a pattern. The vibrations of the shifting tectonic plate boundaries are what causes the shaking sensation of earthquakes.

Q: Can earthquakes cause volcanic eruptions?

A: Sometimes, yes. This is not a common or frequent natural event, but it has occurred. Regional earthquakes greater than magnitude six have been identified as a cause point for nearby volcanic events.

Q: Do earthquakes happen every day?

A: Yes. Thousands of earthquakes are recorded on planet Earth each year.

Q: Have earthquakes increased?

A: This is a tricky question to answer because the answer is both yes and no. Quoting the United States Geological Survey experts, “A temporary increase or decrease in seismicity is part of the normal fluctuation of earthquake rates. Neither an increase nor decrease worldwide is a positive indication that a large earthquake is imminent. According to long-term records (since about 1900), we expect about 16 major earthquakes in any given year. That includes 15 earthquakes in the magnitude 7 range and one earthquake magnitude 8.0 or greater. In the past 40-50 years, our records show that we have exceeded the long-term average number of major earthquakes about a dozen times.”

Q: How do earthquakes affect people?

A: Quakes cause immense destruction and serious damage to infrastructure. When a magnitude five or above quake occurs in an urban area (with the epicenter of the quake occurring in an urban center), the earthquake can destroy the entire infrastructure of that urban area. Some countries (like the United States) have created advanced technologies and building methods to protect buildings and infrastructure from quakes. Other countries, however, are still at high risk of experiencing serious damage from such disaster events.

Q: What is a preliminary earthquake?

A: Another term for this is “foreshock.” A foreshock is a quake that occurs before a larger seismic recording occurs. A foreshock can be a good warning that major quake tremors are just around the corner.

Q: Which cities are most likely to experience strong earthquakes?

A: Cities at high risk for quakes are:

• Tokyo, Japan
• Jakarta, Indonesia
• Los Angeles, California
• Quito, Ecuador
• Osaka, Japan
• San Francisco, California
• Tehran, Iran
• Istanbul, Turkey

Q: Which country has the most earthquakes?

A: The entire nation of Japan rests in an active seismic area. Japan records the most quakes of any country.

Q: Why do earthquakes often cause damaging fires?

A: For the most part, quake events tend to cause fires because tremors damage residential and business gas and electrical lines. That can create natural gas leaks and the downing of power lines, both of which can cause fires.

Q: Are earthquakes increasing in frequency and intensity?

A: Not with any kind of predictability or reliability. Quakes come and go. Some years have more quakes than others. However, there is no way of proving if quakes are becoming more common and more intense than they once were.

Q: Can earthquakes be prevented?

A: Unfortunately, no. According to the USGS, “We cannot prevent natural earthquakes from occurring but we can significantly mitigate their effects by identifying hazards, building safer structures, and providing education on earthquake safety. By preparing for natural earthquakes we can also reduce the risk from human induced earthquakes.”

Q: Can oil drilling cause earthquakes?

A: It’s possible. The USGS has recorded a few instances of serious quakes in Texas, Oklahoma, and other states directly linked to seismic disruptions caused by fracking explosions. From the USGS, “The largest earthquake known to be induced by hydraulic fracturing in the United States was a M4 earthquake in Texas. In addition to natural gas, fracking fluids and saltwater trapped in the same formation as the gas are returned to the surface. These wastewaters are frequently disposed of by injection into deep wells. The injection of wastewater and saltwater into the subsurface can also cause earthquakes that are large enough to be damaging. Wastewater disposal is a separate process in which fluid waste from oil and gas production is injected deep underground far below ground water or drinking water aquifers. The largest earthquake known to be induced by wastewater disposal was a M5.8 earthquake that occurred near Pawnee, Oklahoma in 2016.” That’s one argument for finding alternative, sustainable, and renewable forms of energy production.

http://www.geo.mtu.edu/UPSeis/why.html

http://www.geo.mtu.edu/UPSeis/magnitude.html

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Earthquakes

Learn the science behind how earthquakes happen—and how you can stay safe if one hits.

You feel the ground suddenly shake, and nearby objects are trembling. An earthquake is happening.

Also called a temblor, an earthquake is caused by the movement of parts of the Earth’s crust, its outermost layer. They happen millions of times a year, but most are so small people don’t even feel them.

But powerful earthquakes can cause landslides, tsunamis, flooding, and other dangerous events. Most damage and deaths happen in places where a lot of people live, because the shaking causes windows to break, structures to collapse, fire to break out, and other dangers.

Learn more about these unpredictable Earth tremors—and what to do if one rattles near you.

How earthquakes develop

The action all starts thousands of miles below your feet.

Picture Earth as a hard-boiled egg: Earth’s core is the yolk, and the mantle is the white part. The outer crust is the eggshell.

People live on the surface of the crust. Below the surface—but still within the crust—are tectonic plates. Like gigantic puzzle pieces, these huge slabs of rock encircle the Earth. The seven major plates are named for the regions they rest under: the African, Antarctic, Eurasian, Indo-Australian, North American, Pacific, and South American tectonic plates

Tectonic plates aren't connected but are close together. Where they meet along their edges is called a fault. When heat from the Earth’s core creates currents in the crust, the tectonic plates can scrape, bump, or drag along each other. This is what causes an earthquake—and why the surface sometimes cracks like an eggshell.

How to measure earthquakes

About a half-million quakes rock the Earth every day. Usually the quake is too small, too far below the surface, or too deep in the seafloor to be felt. Some, however, are so powerful they can be felt thousands of miles away.

The spot on the surface just above where an earthquake starts is called the epicenter. Ripples called seismic waves travel out from the epicenter. This causes vibrations that people can feel, sometimes very far from the epicenter.

How far away people can feel an earthquake’s vibrations depends on its size, or magnitude. Scientists base the magnitude on the strength and duration of the quake’s seismic waves. The higher the number, the more powerful the earthquake: A magnitude 3 to 4.9 earthquake is considered minor; 5 to 6.9 is moderate to strong; 7 to 7.9 is major; and 8 or more is an extremely powerful temblor.

As the crust settles after an earthquake, another temblor called an aftershock can happen. Usually, aftershocks are not as powerful as the first quake but can still be very strong.

Geologists can’t predict earthquakes. But they’re working to change that with new research and technology.

Where earthquakes happen

Earthquakes occur along faults, the areas where tectonic plates meet. About 80 percent of earthquakes occur along the rim of the Pacific Ocean. Called the Ring of Fire because of the large number of volcanoes there, the area is a meeting point for many tectonic plates.

Earthquakes are also common in California because the region sits on top of the Pacific and North American tectonic plates. Temblors happen when these two plates grind against each other. About two-thirds of this movement happens along the San Andreas Fault.

Another major earthquake area in the United States is the New Madrid Seismic Zone, which affects Missouri , Arkansas , Tennessee , Kentucky , and Illinois .

How to survive an earthquake

Earthquakes can happen anytime or anywhere—even if you don’t live near a fault. So it’s a good idea to prepare.

• Talk with your family about the safest places in your home in case an earthquake hits. This could be under a sturdy table or next to an interior wall (one that is not connected to the outside).

• Look for heavy items that could fall or break during a quake, and move them to safer spots.

• Ask your parents to make sure you have an emergency kit containing things like first-aid supplies, a flashlight, a cell phone charger, and a battery-operated radio. Your family should also have enough food and water for at least 72 hours

DURING AN EARTHQUAKE: Most earthquakes last only 10 to 30 seconds, so it’s important to get to a safe place fast. Remember three things during an earthquake: drop, cover, and hold on.

Drop:  Get down on your hands and knees and crawl to your shelter.

Cover:  Underneath a sturdy table, desk, or bed, cover your head and neck with your arms. If furniture isn’t nearby, crouch down on your knees with your arms over your head and neck next to an interior wall. (Don’t stand under a doorway—they can easily collapse.)

Hold on:  If you’re under a piece of furniture, hold on with one hand and move with the furniture if it starts sliding. Stay where you are until the shaking stops.

AFTER AN EARTHQUAKE: Once the earthquake ends, check for injuries. Listen to a radio for any warnings and instructions from official organizations like the United States Geological Survey. Be prepared for any aftershocks.

Text and images adapted from Everything Volcanoes and Earthquakes: Earthshaking photos, facts, and fun!

( Learn more about earthquakes at National Geographic .)

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Earthquake preparedness of households and its predictors based on health belief model

Masoumeh rostami-moez.

1 Research Center for Health Sciences, Hamadan University of Medical Sciences, Hamadan, Iran

2 Vice-chancellor for Health, Hamadan University of Medical Sciences, Hamadan, Iran

Mohammad Rabiee-Yeganeh

Mohammadreza shokouhi.

3 Chronic Diseases (Home Care) Research Center and School of Nursing & Midwifery, Hamadan University of Medical Sciences, Hamadan, Iran

Amin Dosti-Irani

4 Department of Epidemiology, School of Health, Hamadan University of Medical Sciences, Hamadan, Iran

Forouzan Rezapur-Shahkolai

5 Department of Public Health, School of Public Health, Hamadan University of Medical Sciences, Shahid Fahmideh Ave, Hamadan, Iran

6 Social Determinants of Health Research Center, Hamadan University of Medical Sciences, Hamadan, Iran

Associated Data

The analyzed datasets during this study are available from the corresponding author on reasonable request.

Earthquakes are one of the most destructive natural disasters in which many people are injured, disabled, or died. Iran has only 1 % of the world’s population, but the percentage of its earthquake-related deaths is absolutely higher. Therefore, this study aimed to determine the level of earthquake preparedness of households and its predictors using the Health Belief Model (HBM).

This observational descriptive and analytical study was conducted on 933 households in Hamadan province, located in the west of Iran, in 2019. Multi-stage cluster random sampling was used for selecting the participants. The inclusion criteria were being at least 18 years old and being able to answer the questions. A questionnaire was used for data collection including earthquake preparedness, awareness of earthquake response, predictors of earthquake preparedness based on the HBM, and demographic information. Analysis of variance, independent t-test, and a linear regression model was used.

The mean age of participants was 38.24 ± 12.85 years. The average score of earthquake preparedness was low (approximately 30%). There was a significant relationship between earthquake preparedness and gender ( P  < 0.001), homeownership ( P  < 0.001), marriage status ( P  < 0.001), education ( P  < 0.001), and previous earthquake experience ( P  < 0.001). Regarding the HBM constructs, perceived benefits ( P  < 0.001), cues to action ( P  < 0.001), and self-efficacy ( P  < 0.001) were significant predictors of earthquake preparedness.

Conclusions

Earthquake preparedness was insufficient. Besides, perceived benefits, cues to action, and self-efficacy were predictors of earthquake preparedness. These predictors can be taken into account, for designing and implementing related future interventions.

Earthquakes are one of the most dangerous natural hazards that occur suddenly and uncontrollably. They cause physical, psychological, and social damages in human societies [ 1 ]. Over the past two decades, 800 million people have been injured by natural disasters. Besides, natural disasters have caused 42 million deaths in the world [ 2 ]. Iran is always at risk of earthquakes due to its geographical location on the Alpine-Himalayan orogenic belt [ 3 , 4 ]. More than 70% of the major cities in Iran are vulnerable to substantial damages. The earthquakes of recent decades have not only caused the deaths of thousands but also have caused massive economic damage and destroyed many cities and villages in the world [ 5 , 6 ]. Iran has only 1 % of the world’s population, but the percentage of its earthquake-related deaths is absolutely higher [ 7 ]. The disaster management cycle has four phases including mitigation, preparedness, response, and recovery. Preparedness is the most important phase in the disaster management cycle. Previous research in Iran has shown that the role of people as the most important and largest group has often been neglected in disaster preparedness program planning [ 8 ].

The Health Belief Model (HBM) describes the decision-making process that individuals use to adopt healthy behavior. It can be an effective framework for developing health promotion strategies [ 9 ]. Theoretically, in the HBM, perceived susceptibility, perceived severity, perceived benefits, perceived barriers, cues to action, and self-efficacy (the beliefs of individuals in their ability to prepare for disaster) predict behavior [ 1 , 9 , 10 ].

There are some studies on earthquake preparedness that have assessed the readiness of individuals based on their knowledge and skills [ 11 – 15 ]. Some studies have also considered structural and non-structural safety in some cities [ 16 ] and some studies have investigated students’ readiness [ 17 , 18 ]. There are a few studies that have used behavioral change models in the disaster area [ 5 ]. The Haraoka and Inal used the Health Belief Model to develop a questionnaire for earthquake preparedness [ 1 , 11 ].

Previous studies in Iran showed that most households did not have enough readiness and had a relatively high vulnerability to possible earthquake hazards [ 19 , 20 ]. Also, one study showed that improving the socio-economic status was correlated with improving the attitude of people about disaster preparedness [ 13 ]. In DeYoung et al.ʼs study, earthquake readiness was positively correlated with risk perception, self-efficacy, and trust in information about hazards through media [ 21 ].

To the best of the authors’ knowledge, this is the first study in Iran that examines earthquake preparedness of households, using a behavior change model. Considering the importance of earthquake preparedness of households, this study aims to asses the level of earthquake preparedness of households and its predictors based on HBM.

Study design and participants

This observational descriptive and analytical study was carried out in all counties of Hamadan province, located in the west of Iran, in 2019. These counties includes Hamadan (the capital of Hamadan province), Malayer, Tuyserkan, Nahavand, Razan, Bahar, Kabudarahang, Asadabad, and Famenin. Based on the previous study [ 19 ], the estimated sample size was 600 households. Cluster sampling was used for this study and we used the design effect of 1.5 plus 10% attrition. Subsequently, the final sample size was calculated at 1000 households. The data were collected from February to July 2019. From each county, a university graduate person was recruited and trained for data collection. The supervision and training were done by the first author. The verbal informed consent was obtained from all participants before the data gathering. The participants were first provided a description of the study and they were informed that the participation in the study was voluntary, and all study data were anonymous and confidential. Then, if they gave verbal informed consent, they would participate in the study and fill out the anonymous questionnaires. A person aged 18 or above was randomly selected from each household and answered the questions. For illiterate people, questionnaires were filled out through interviewing them. The inclusion criteria were being at least 18 years old and being able to answer the questions. The exclusion criteria were an incomplete questionnaire.

Participants have been selected by multi-stage cluster random sampling. First, stratified sampling was used for each county based on its urban and rural populations. Then, in urban and rural areas, a list of urban or rural health centers was listed and one health center was randomly selected in each county. After that, from the list of all households covered by the selected health center, one household was selected by simple random sampling and sampling started taking the clockwise direction of the selected household and continued until the required sample was collected. For selecting the sample of the urban population of Hamadan County, we selected one health center from each district by simple random sampling (in Hamadan city, there are four districts). In the next stage, from the list of covered households, one household was randomly selected and the sampling was started taking the clockwise direction until the required sample in each district was collected.

Measurements

The questionnaire used for data collection comprises four domains including 1) demographics, 2) earthquake preparedness 3) awareness on earthquake response, and 4) predictor of earthquake preparedness based on the HBM. Earthquake preparedness was response variable.

• Demographics included age, sex, occupation, education, economic status, family size, number of individuals over 60 years old and under 16, earthquake experience, homeownership, marital status, and having a person with a disease that needs medication at their home.
• We measured earthquake preparedness by an earthquake preparedness checklist [ 22 ]. This checklist was developed and validated by Spittal et al., in 2006. It consists of 23 questions with yes or no answers. The questions are about: having a working torch (flashlight), a first aid kit, a working battery radio, a working fire extinguisher, etc. [ 22 ]. We adapted this checklist by adding two items according to the context of the study. These two questions were: 1) do you know the necessary contact numbers such as fire station, police, and emergency so that you will be able to call them if needed?; 2) are you familiar with the phrase, “Drop, Cover, and Hold”? Also, we adapted it with some minor changes. We added “have learned first aid” to “have purchased first aid kit” statement. We added “and extra cloths and blankets” at the end of” put aside extra plastic bags and toilet paper for use as an emergency toilet” statement. We replaced “roof” with “my way” in “ensuring that the roof will probably not collapse in an earthquake. We added some examples to “take some steps at work” statement such as attending an earthquake preparedness class and having fire insurance. The content validity of the Persian checklist was tested by 10 experts. We calculated CVI and CVR equal to 0.92 and 0.95, respectively. Also, the face validity and reliability of this checklist were examined in a pilot study on 40 adults. According to their recommendations, minor revisions were made to increase the transparency and understandability of the statements. Likewise, the reliability of this checklist was measured by internal consistency (Chronbach α = 0.858). The total score of this checklist was ranging from 0 to 25 and the higher score reflects more preparedness.
• The awareness on earthquake response questionnaire included seven questions with true/false answers (In an earthquake: you should get down close to the ground; you should get under a big piece of furniture such as a desk or other covers; you should hold on to a firm object until the end of the shaking; you should stand in a doorway; If you are indoors during an earthquake, you must exit the building; If you are in bed during an earthquake, you should stay there and cover your head with a pillow; next to pillars of buildings and interior wall corners are the safe areas). One point was given for each correct answer. Therefore, the total score of this domain was seven points.
• The adapted questionnaire of earthquake preparedness based on the HBM was used. The original questionnaire has been established and validated by Inal et al. [ 1 ] in Turkey. The forward and backward translation method was used for translating the original questionnaire. According to the experts’ opinions, some minor changes were made to adapt the items of the questionnaire for the study population in the present study. Thereby, three questions were added to the questions of the cues to action (Radio and TV encourage me to prepare for disasters, I usually seek information about disaster preparedness from Radio and TV, and I usually obtain information about disaster preparedness from health providers). Besides, one question was added to the questions of perceived benefits (preparedness for disaster will reduce financial losses and injuries). Then, the content validity of the questionnaire was assessed by a panel of experts including 10 Health specialists in the field of health in disasters, health education, health promotion, and safety promotion (CVR = 0.92 & CVI = 0.85). Next, the face validity and reliability of the questionnaire were measured in a pilot study on 40 people over 18 years old. The reliability was calculated by using internal consistency. One question from the perceived severity (emergency and the experience of disasters does not change my life) and one question from self-efficacy (I cannot create an emergency plan with my neighbors) was excluded based on the results of Cronbach’s alpha. In Iran, neighbors don’t share their plans; therefore, it was logical to exclude these items. Finally, the questionnaire consisted of 33 questions, including perceived severity (2 questions, α = 0.709), perceived susceptibility (6 questions, α = 0.664), perceived benefits (4 questions, α = 0.758), perceived barriers (6 questions, α = 0.822), self-efficacy (7 questions, α = 0.677), cues to action (8 questions, α = 0.683), and total questions (33 questions, α = 0.809). All of the items were assessed by a 5-point Likert scale ranging from ‘completely disagree’ (one point) to ‘completely agree’ (5 points). Some items were scored reversely.

Statistical analysis

We used the analysis of variance (ANOVA) and independent t-test to determine the relationship between variables. Besides, the multivariate linear regression model was used to determine the predictors of household earthquake preparedness. The Stata 14.2 software was used to analyze the data.

In this study, 933 questionnaires were analyzed (response rate: 93.3%). The mean age of participants was 38.24 ± 12.85 years. Besides, 228 (24.44%) participants were male and 656 (70.31%) were female. About 80% of the participants did not have an academic education and had a diploma degree or less than a diploma degree. Also, 573 (61.41%) participants were homeowners (Table  1 ).

Basic and demographic characteristics of participants of earthquake preparedness study

The earthquake preparedness of the participants was low. The household preparedness score was 7.5 out of 25. In other words, the average earthquake preparedness of households was approximately 30%. Besides, the self-efficacy score was 60.79 ± 0.55 and the score of cues to action was 66.57 ± 0.45 (Table  2 ).

The mean scores (in percentage) of earthquake preparedness, constructs of Health Belief Model, and earthquake performance awareness of participants

The participants’ preparedness for the earthquake had a significant relationship with gender ( P  < 0.001), homeownership ( P  < 0.001), marital status ( P  < 0.001), and previous experience of a destructive earthquake ( P  < 0.001). Also, the mean score of earthquake preparedness was higher in those who reported moderate or good economic status. The mean difference was statistically significant by the Scheffe test ( P  < 0.001). Furthermore, the one-way ANOVA/Scheffe’s test showed that there was a significant difference between illiterate people and those who had either university education or diploma degree and similarly, a significant difference in earthquake preparedness was observed between primary education and those who had either academic education or diploma degree ( P  < 0.001) (Table  3 ).

The relationship between earthquake preparedness and demographic variables of participants by Independent T-Test and Analysis of Variance

The crude regression analysis showed that all constructs of the HBM except perceived severity were significant predictors of earthquake preparedness (P < 0.001) but after using stepwise regression, only perceived benefits ( P  < 0.006), cues to action ( P  < 0.001), and self-efficacy ( P  < 0.001), significantly predicted the earthquake preparedness (Table  4 ).

The relationship between earthquake preparedness and study variables, using Stepwise Linear Regression

In this study, we determined the level of earthquake preparedness of households and its predictors based on HBM. The earthquake preparedness of the participants was low. The participants’ preparedness for the earthquake had a significant relationship with homeownership, education, and previous experience of a destructive earthquake. Also, perceived benefits, cues to action, and self-efficacy significantly predicted the earthquake preparedness.

Despite the strong emphasis on earthquake preparedness to prevent its damaging effects, the findings of this study showed that most people had low preparedness for earthquakes which is similar to the findings of previous studies [ 18 , 23 – 25 ]. This can be very dangerous in areas that are vulnerable to earthquakes. Earthquake preparedness is related to the previous experience of destructive earthquakes and their damaging consequences. Households that had previously experienced destructive earthquakes were more prepared than those who had not previously experienced this event, which is similar to previous finding [ 26 , 27 ]. People who live in earthquakes zones and understand the potential losses from earthquakes are more likely to be prepared in comparison to people living in other areas [ 18 ]. This could be due to recalling previous injuries as well as the fear of recurrence of similar injuries in future earthquakes. This goes back to the culture of societies that their members don’t believe that they are at risk of the occurrence of hazards and their consequences until they experience these hazards. Regarding the high frequency of earthquakes in the Hamadan province, most of the participants in this study had previous earthquake experience but they were not prepared for earthquakes. Perhaps this is because most of the recent earthquakes in Hamadan did not result in deaths and as a result, these households do not take the risk of earthquakes seriously and do not find it essential to hold earthquake preparedness [ 28 ].

Besides, education was significantly correlated with households’ earthquake preparedness, which is similar to the results of the studies by Russell et al. and Ghadiri & Nasabi [ 29 , 30 ]. One explanation can be that people with higher education are more knowledgeable, more aware of earthquakes danger, and more inclined to acquire new skills [ 28 , 31 ].

In this study, we found that the preparedness of participants has a significant relationship with homeownership. Two previous studies showed homeowners were more prepared for earthquakes than renters [ 32 , 33 ], whereas a study in Ethiopia in 2014 showed that homeownership had no relationship with disaster preparedness [ 28 ]. One of the explanations is that owners can make the necessary changes despite preparedness costs due to place attachment, but more studies are required to confirm the role of homeownership.

We adjusted for multiple possibly confounding factors in our analysis. After adjusting the model, perceived benefit, cues to action, and self-efficacy had significant predictors of earthquake preparedness. It is more possible that people’s earthquake preparedness increases when they are aware of the benefits of earthquake preparedness. Furthermore, people with high self-efficacy feel they can prepare for earthquakes [ 34 ]. On the other hand, people may find the earthquake hazardous but if they feel enough confident to reduce damages of earthquakes, they will engage in preparedness. If people perceive the benefits of a healthy behavior higher than the barriers of it, they will engage in that healthy behavior. Therefore, people may perceive earthquakes as a high threat but it can be expected that higher perceived benefits and self-efficacy among them result in higher preparedness. One possible explanation is that the perceived benefits motivate people to perform a specific behavior and adopt an action [ 10 ]. Besides, the significant association of self-efficacy with preparedness at the household level for earthquakes could be explained by the positive and strong association of cues to actions with earthquake preparedness at the household level. Self-efficacy can be improved by observational learning, role modeling, and encouragement. Self-efficacy affects one’s efforts to change risk behavior and causes the continuation of one’s safe behavior despite obstacles that may decrease motivation [ 10 ]. Moreover, cues to action associated with earthquake preparedness [ 1 ]. Cues to action mention to influences of the social environment such as family, friends, and mass media. Mass media can play a vital role in educating the public about earthquake preparedness.

This study has several limitations. Firstly, using a self-reporting approach for data gathering, and secondly, due to the low number of relevant studies on earthquake preparedness based on behavioral change models, it was less possible to compare different studies with the findings of this study. Third, it should be noted that the results of this study can be generalized in the study population and setting, but for other settings it should be done with caution. Despite these limitations, this study had some strengths, we use a theoretical framework for identifying factors that influence earthquake preparedness with a large sample size. Also, the findings of this study are useful for emergency service providers, health authorities, and policymakers in designing and implementing earthquake preparedness programs. This research is also useful for researchers as it can be used as a basis for future researches. It is recommended to design and implement interventions to improve household preparedness for an earthquake based on self-efficacy, perceived benefits, and cues to action.

Households’ earthquake preparedness was insufficient and low. Controlling the damaging consequences of earthquakes is related to the preparedness for earthquakes and can prevent its devastating effects. Perceived benefits, cues to action, and self-efficacy had a significant relationship with earthquake preparedness. The possibility of people being more prepared is increased when they are aware of and understand properly the benefits of being prepared for earthquakes and other disasters. People with high self-efficacy also feel more empowered for taking better care of themselves and their families during disasters. Cues to action would also encourage earthquake preparedness. Since health centers and TV and radio programs were the primary sources of learning about earthquakes for the people, it is recommended that broadcasting provides related programs and educates people about earthquake preparedness. The predictors that were assessed in this study can be taken into account for designing and implementing proper interventions in this field.

Acknowledgments

The authors gratefully thank all of the participants in this study.

Abbreviations

Authors’ contributions.

MRM has made substantial contributions to the conception and design of the study, took responsibility for and coordinated the acquisition of data and contributed actively in the analysis of the data and the writing of the manuscript. FRS has made substantial contributions to the conception and design of the study, interpretation of the data, and writing up the manuscript. MS contributed to the design of the study and preparation of the manuscript. MRY was involved in the design of the study and the data gathering process. ADI contributed to the study design, data analysis, and interpretation. All authors read and approved the final manuscript.

This study was approved and financially supported by the Deputy of Research and Technology of Hamadan University of Medical Sciences (number: 9707174168). The funder of this study had no role in the study design, data collection, data analysis, data interpretation, or writing the manuscript.

Availability of data and materials

Ethics approval and consent to participate.

This study was approved by the Ethical Committee of Hamadan University of Medical Sciences (approval code: IR.UMSHA.REC.1397.359). This study was an observational questionnaire study and the anonymous questionnaires were used to collect data. Therefore, the verbal informed consent was obtained from all participants prior to participation in the study and filling out the questionnaires. The form of consent was approved by the ethics committee.

Consent for publication

Not applicable.

Competing interests

All authors declare that they have no competing interests.

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