Earthquakes and Faults

Of all 50 states in the U.S., Washington has one of the highest risks of large and damaging earthquakes because of its geologic setting and population distribution. Earthquakes occur daily in Washington, though most of them are too small to be felt or cause damage. Large earthquakes (greater than magnitude 5) are much less frequent, but when they occur, people can feel the shaking across a large area, and the shaking can cause significant damage to buildings, roads, bridges, dams, and utilities.

On this page:

• The Science of Faults and Earthquakes
• Earthquake Sizes: Magnitude and Intensity Scales
• Earthquakes in Washington
• Geologic Hazards Associated with Major Earthquakes
• How to Assess Your Personal Earthquake Risk
• Seismic Risk Resources
• Prepare Yourself for Earthquakes
• An earthquake just happened and I want more information
• WGS Earthquake Data Products and Projects

The Science of Faults and Earthquakes

When a fault slips suddenly, it creates an earthquake which is a release of energy in the form of ground-shaking waves that affect humans and their built environment. This section explains what faults are and how they create earthquakes. Read the topics below if earthquakes are new to you or you want to develop a deeper understanding of earthquake processes and causes, as well as approaches scientists use to study them with an eye toward protecting the public.

What is a Fault?

Faults are fractures in Earth’s crust where rocks on each side are visibly offset. Earthquakes happen when rocks slide past one another along a fault. Faults can be any size from a few inches to over a thousand miles long. Larger faults are studied more closely because they can produce larger earthquakes.

Geologists sort faults into three categories based on the fault’s orientation (is it a vertical surface or tilted surface?) and how rocks are offset across the fault (did they slip horizontally past each other, or up and down?).

Plate Tectonics

Plate tectonics is a theory that describes how the outer, rigid layer of the Earth (the lithosphere) is divided up into plates that move relative to one another. The forces created when tectonic plates collide, separate, or slide past one another are what cause faults and earthquakes. UNAVCO has a video about plate tectonics and how different types of plate motions produce earthquakes.

Washington’s Tectonic Setting

Washington State is located on the western edge of the North American tectonic plate near the boundary between the North American plate and the Juan de Fuca plate. The Juan de Fuca plate is slowly moving eastward and being pushed under the North American plate, a process called subduction. The boundary between the two plates is a large fault called the Cascadia subduction zone.

Geologic Settings Where Earthquakes Occur

Plate Boundaries

Most of the earthquakes on Earth occur within approximately 300 miles of plate boundaries, where the forces due to plate tectonics are greatest. In Washington, in addition to the Cascadia subduction zone, there are many shallow faults that cut across the state as far east as Walla Walla, as well as deep faults (within the subducting Juan de Fuca plate) all of which can cause earthquakes far below the Earth’s surface.

Intraplate Faults

Earthquakes also occur on faults located in the interiors of plates, for example, in Missouri, Oklahoma and Virgina in North America. Earthquakes along these faults happen in response to non-tectonic forces. Though earthquakes can happen in far eastern Washington, that region is still part of the very wide plate boundary and are not considered intraplate faults.

Active Volcanoes

Earthquakes also occur when melted rock (magma) moves within the Earth. Active volcanoes in the Cascade Range are a source of this type of earthquake in Washington. Such earthquakes alerted scientists in 1980 that Mt. St. Helens was becoming active, weeks before it erupted. Volcanic activity also heats fluids in the surrounding rock that then circulate through cracks in the crust changing local forces that allow earthquakes to take place. Scientists at the Cascades Volcano Observatory (CVO) use earthquakes, along with other techniques, to monitor volcanic activity at Washington’s many volcanoes. Increased earthquake activity can warn us of a likely eruption in the near future and allow scientists and emergency managers to get people out of harm’s way.

Active Versus Inactive Faults

Rocks are always in motion due to the movement of the tectonic plates, and plate tectonics has been ongoing for billions of years. This means that the faults in Earth’s crust span a huge range of ages; some faults are very old and others are relatively new. Faults that could produce an earthquake in the present day are called ‘active faults’ by geologists.

How Geologists Find Faults

Finding faults and knowing how often they move (or ‘rupture’) is one of the most important tasks for geologists to keep society safe from earthquake hazards. There are many faults that have not been discovered because they are concealed by vegetation or young sediment. Other faults have not been discovered because detailed geologic studies necessary for finding them have not been completed. There are also known faults that are poorly understood. Finding and mapping all of these faults is an important mission of the Washington Geological Survey and other institutions (such as universities and the U.S. Geological Survey).

In much of Washington, because dense vegetation covers the land and makes mapping the distribution of rock types at the surface difficult, scientists supplement geologic mapping with other types of investigations to find hidden information under vegetation and in the subsurface. Therefore, finding and learning about faults requires many different tools and methods. Collectively, this information can provide a complete history of a fault’s past movements.

Geologic Mapping

The careful on-the-ground observations of rock types and their distribution across the Earth’s surface is called geologic mapping.  This method is of primary importance, and the other techniques described below often serve to enhance interpretations made from mapping. Our Geologic mapping web page describes mapping techniques in more detail.

Lidar

Lidar images show a 3D view of the topography of Earth’s surface at high resolution (as many as two elevation measurements per square foot, and sometimes more). This method can show offset of the Earth’s surface along a fault (a ‘scarp’) that would be hard to see from an airplane, drone, or even when standing on the ground next to the fault. WGS has a team of scientists focused entirely on collection, quality control, and archiving of Washington lidar data. Learn more on the WGS lidar page, or by watching this video from IRIS showing how lidar helps scientists find faults.

Geophysics

There are many geophysical methods that can be used to find buried faults and to spot faults that have recently (in the last few hundreds to thousands of years) had a surface rupturing earthquake that caused offset at the ground surface. Geodetic methods that track how the surface of the Earth moves over time are useful for finding faults that have recently experienced offset or show signals that a fault could be active. An array of geophysical methods can image physical properties of subsurface rocks. For example, one of these techniques is seismology, which measures how quickly seismic waves travel through different layers of the Earth. Gravity and magnetics are other geophysical methods that can measure the density and magnetic properties of rocks in the subsurface. Each of these subsurface techniques can show offsets in rock layers that may arise from rock movement along faults.

Trenching

Once geologists have located a new fault, they often have to dig into the sediment covering the fault to expose stratigraphic layers that record time. Geologists carefully measure how the fault has moved and displaced the layers of soil and rock over time. The age of the highest layers of soil and rock offset by the fault indicates the last time the fault was active.

Dating Soils and Rocks

When geologists think they have found a new fault that they suspect is young and active, they will send samples of soils collected near the fault to a lab for dating. One particularly useful type of age dating is radiocarbon dating. In this method, any sort of living material that contains carbon, such as the remains of plants or animals, can be analyzed to see how it has radioactively decayed over time. In radioactive decay, parent isotopes slowly and steadily decay to the daughter isotopes at a known pace described by the parent isotope’s half-life. Scientists measure the ratio of parent isotopes to daughter isotopes to estimate how much time has passed since the material was originally deposited. The oldest age that is possible to measure with the radiocarbon dating method is about 50,000 years, so it’s very useful for determining the age of geologically young and active faults. Isotopes other than carbon can provide dates for soils and rocks that are more than 50,000 years old.

How Faults Cause Earthquakes

 The earth is constantly shifting and moving, largely due to plate tectonic processes as described above. Faults accommodate this motion. When there is sudden movement of rocks on either side of a fault (called a rupture), seismic energy is released. Seismic energy spreads throughout the Earth in the form of seismic waves that travel at thousands of miles per hour. The sudden energy release is called an earthquake, and the seismic waves generated are what cause the ground shaking that people experience from the earthquake. The process that creates the sudden movement involves a few steps that repeat over time called the stick-slip cycle.

Rocks on either side of a fault rarely move past each other smoothly. Quite often there is roughness or a snag between the rocks on either side of the fault, this roughness is also referred to as friction and the rocks get stuck together right along the fault. Away from the fault, the rocks are still moving, creating a bend. This bending stores elastic energy, the same type of energy stored in a stretched rubber band or an uncooked spaghetti noodle when you bend it. When there is finally enough force from the bending to overcome the friction holding both sides of the fault in place, the rocks on either side of the fault slide past each other extremely quickly (in a fraction of a second to a few seconds), releasing seismic energy: this sudden movement is an earthquake. We call the time between earthquakes, when friction causes the fault to ‘stick,’ the interseismic period. The time it takes for the fault to ‘slip’ (which is the earthquake itself) is called the coseismic period. The repeated pattern of interseismic and coseismic periods on a fault over time is called the stick-slip cycle. Most earthquakes that happen are too small to be felt by people, but sensitive seismometers located all over the world can measure this seismic energy. Generally, only large earthquakes (at least magnitude 5.5) cause deformation like scarps at the ground surface, these earthquakes occur far less frequently than small earthquakes (less than magnitude 5).

In Washington, most earthquakes are related in some way to the Cascadia subduction zone. The fault interface between the Juan de Fuca and North American plates can produce very large, megathrust earthquakes, because these two plates are grinding against each other and getting repeatedly stuck and unstuck as part of the stick-slip cycle. Additionally, the movement of these large tectonic plates exerts force inland of the subduction zone, causing faults in the interior of Washington, and faults within the subducting Juan de Fuca plate sliding beneath Washington, to also stick and release over time and produce earthquakes.

The video below from IRIS shows a demonstration of the stick-slip cycle of the Cascadia subduction zone:

What is an Active Fault?

While there are many faults in Washington State, some of them are geologically very old (100 million years old, for example) and inactive, meaning they haven’t produced an earthquake in a very long time and are not likely to do so in the future based on our understanding of forces acting in the Earth today. Therefore, they do not create an earthquake hazard. On the other hand, an ‘active’ fault has evidence for movement within the past 10,000 years, so it could have an earthquake in the future. While 10,000 years seems like a long time to us, it’s not very long geologically speaking, and it’s reasonable to assume that one of these active faults could create an earthquake at any time. Scientists from the Pacific Northwest Seismic Network and the U.S. Geological Survey monitor known faults with seismometer networks to help us understand more about the seismic activity of these faults.

Knowing if a fault has moved (or ‘ruptured’) and caused an earthquake recently is important to help scientists determine the potential for future earthquakes on that fault. By knowing when a fault last ruptured in a large earthquake that deformed the ground surface and studying the geologic record to see how often (on average) a fault has experienced surface rupturing earthquakes in the past (sometimes over the course of a million years or more), scientists can forecast when the next earthquake may be. See other parts of this web page to learn more about earthquake forecasting.

WGS Fault Maps

The Geologic Information Portal has layers for active faults and earthquakes in Washington. To learn more about how these data could be used to evaluate your seismic risk, see the Future earthquakes in Washington section below.

Earthquake Sizes: Magnitude and Intensity Scales

Scientists use the term ‘earthquake’ for the energy release created by sudden fault movement. Many members of the public use ‘earthquake’ for the shaking people feel due to seismic waves. This mismatch can create confusion. This section explains the two main ways scientists describe earthquakes, particularly their size, which can help people understand both the underlying physical event and its effect on human lives. Read the sections below if you want to make sense of earthquake reporting both by scientists and the media; it will also help you understand scientific maps and earthquake forecasting products for planning your life and community in earthquake country.

The sizes of earthquakes (magnitude), and the intensity of the shaking they cause (intensity), are described using multiple scales that can be easily misunderstood and confused with one another. The magnitude of an earthquake is a measure of how much energy was released by the earthquake, whereas the intensity of the earthquake is a measure of how much shaking and damage the earthquake caused at any given place on the Earth’s surface. The shaking intensity felt at a given place on the Earth’s surface for an earthquake with a given magnitude will strongly depend on distance of that place from the place where the earthquake originated. As a general rule of thumb, places closer to the fault that created the earthquake will experience higher intensity shaking from the earthquake than places that are farther away.

Earthquake shaking intensity also depends on what kind of rocks or sediment makes up the earth at the place that is experiencing shaking, the type of fault that ruptures, and at what depth in the earth the earthquake originated. Read the sections below to learn more about earthquake magnitude, intensity, and the types of earthquakes in Washington. 

Earthquake Magnitude

 There are multiple ways to measure and report an earthquake’s magnitude, and you’ve probably heard about the Richter magnitude. The Richter scale was developed in southern California in 1935 and was replaced by the moment magnitude scale in the late 1970s to account for progress in earthquake recording instrumentation and improvement in our understanding of how earthquakes happen. News reports still often use the term Richter, even though what they are actually reporting is moment magnitude.

The moment magnitude scale (represented by the symbol Mw) is the scale used by scientists today. Mw accounts for the physical properties of the rocks along the fault, the size of the area of the fault that moved during the earthquake, and what distance rocks on either side of the fault moved. The greatest influencing factor on earthquake magnitude is the length of the fault that slips during an earthquake. The moment magnitude scale is a more accurate method than Richter for reporting earthquake magnitudes and relating earthquake sizes worldwide, and it is the one we use on this webpage. On occasion, scientists use M generically to denote earthquake magnitude without identifying the specific magnitude scale.

Both the Richter scale and the moment magnitude scale are logarithmic. Each magnitude increase of 1 means ~32 times more energy is released. An increase of 2 means that ~1,000 times more energy is released. For example, a magnitude 7 earthquake releases 32 times more energy than a magnitude 6 earthquake, and 1,024 times more than a magnitude 5 earthquake.

Earthquake Intensity

 The amount of shaking a location (or a person in that location) experiences from an earthquake, also called earthquake intensity, does depend on the magnitude, or the energy release from the fault. However, it also depends on how far away you are from the fault that creates the earthquake, as well as other factors like the type of fault that created the earthquake, the local rock and soil beneath you, and even the structural integrity and design of the building you are in.

The fault that creates the earthquake sets the initial energy release that then moves through the ground as seismic waves. Larger magnitude earthquakes create stronger (or if you are thinking about waves, ‘higher amplitude’) and longer duration shaking. The type of fault that moves to create the earthquake also influences both the amount of energy initially sent in different directions from the fault and how much that energy is piled up or spread out in any given direction (called the ‘directivity’ effect by scientists), creating more shaking in some regions nearby the fault than others.

After magnitude, distance to the earthquake source has the biggest effect on the shaking that happens in any given location. For any energy source (think about a lightbulb, for example), the further away you are from that energy source, the more the energy is dissipated before it reaches you (light from a bulb is dimmer the farther away it is from you–see an illustration of this below). Since earthquake energy travels as a seismic wave, and this wave is what creates ground shaking, the further away any surface location is from the earthquake source, the less shaking a person will feel at that location.

Scientists call the location deep within the Earth where the earthquake occurs the hypocenter, whereas they call the point on the Earth’s surface that is directly above the earthquake the epicenter. The depth of the hypocenter and distance from the epicenter of the earthquake to any surface location are both important factors in determining earthquake intensity at that location. The deeper the earthquake, the less shaking all locations near the epicenter will feel. In Washington State, earthquakes occur along faults across a wide range of depths, which greatly affects earthquake intensity felt at the surface.

Additionally, the type of rock or soil within the ground right underneath a person or structure can amplify or diminish those incoming seismic waves further. In general, looser soils will amplify seismic energy, causing more violent shaking during an earthquake, and more rigid rocks will not amplify energy, causing less shaking. 

The Modified Mercalli Intensity Scale

The Modified Mercalli Intensity (MMI) scale is a way to measure the intensity of an earthquake. It is a qualitative scale that ranges from I–XI (1–11) and measures the amount of shaking and damage caused by an earthquake. For earthquakes that occurred before seismographs were invented, the Mercalli Intensity scale was used to make maps of damage and determine the size and location of an earthquake. Scientists use this scale in modern times to refine damage maps for earthquake emergency response and to create scenarios for the shaking and damage people might expect from future earthquakes.

Intensity Comparison: The 1994 Northridge Earthquake and the 2001 Nisqually Earthquake

Above are two ShakeMaps that the U.S. Geological survey produced after the Northridge earthquake in 1994 and the Nisqually earthquake in 2001. They show the intensity of shaking felt during these earthquakes within the region around the epicenter on the surface of the Earth, using the MMI scale. See the Seismic ShakeMaps and Scenarios section below to learn more about how scientists make and work with ShakeMaps. These maps illustrate several earthquake intensity effects very well. First, the magnitudes of these two earthquakes are very similar, therefore most of the difference we see between these two maps have to do with intensity effects. Overall, the Northridge earthquake shook a larger area with greater maximum intensities (up to extreme) than the Nisqually earthquake. That is because the Northridge earthquake was much shallower (13 km or 8 miles deep) than the Nisqually earthquake (52 km or 32 miles deep). Note that even at similar distances from the epicenter, the intensity of shaking varies greatly. Some of these differences look patchy and this is due to differences in shallow soil and rock beneath different locations. There is also a large patch of violent to extreme shaking north of the Northridge epicenter. This resulted from a phenomenon called directivity: the fault rupture started in the south and propagated north causing greater intensity shaking to the north.

View the video below from IRIS to learn more about magnitude and intensity.

Building Response to Shaking

Though not part of scientific calculations of earthquake intensity, when seismic waves shake buildings, the materials composing the building and its design can have an impact on the shaking that people inside will feel. Buildings of different heights and construction materials respond differently to the same intensity of ground shaking. If buildings are unable to accommodate or bend with the earthquake motions without breaking, the buildings tend to collapse or suffer significant damage. One of the consequential effects of magnitude and intensity for buildings is the duration of shaking. Duration of shaking is longer for larger magnitude earthquakes and can also be longer for areas where the shallow ground is made of softer rock or soil. The longer a building shakes, the more damage can occur. The ground shaking from the earthquake and its effect on structures is the biggest risk during an earthquake, but luckily, this factor is also one we can control. Seismic retrofits to existing buildings can greatly reduce the risk of damage and casualties, and creating new buildings with seismic hazards in mind can do the same.

Demonstration of how earthquake magnitudes increase: The Pasta quake!

You can try this experiment at home! Grab an uncooked spaghetti strand and slowly bend it (storing elastic energy) until it breaks. You can feel the buildup of elastic energy as it bends.  When it finally breaks, that’s similar to the energy release of an earthquake.  If the single spaghetti strand represents the energy released by a magnitude 5 earthquake, then a magnitude 6 earthquake would be equivalent to breaking a bundle of 32 strands at once, and a magnitude 7 would be like breaking 1,024 strands.

Continuing the analogy, below is an image of how many strands are equivalent to a magnitude 8.

Earthquakes in Washington

Many past earthquakes have happened during human habitation in Washington State, but not all earthquake sizes or locations are currently emphasized in the media. Read this short section for a summary of the best available science on past earthquakes in Washington. You might be interested in this section if you want to understand how past earthquakes may inform planning for our future as individuals and communities.

Earthquakes From Written History

A critical component for assessing current earthquake hazards is looking at the record of past earthquakes. There have been about 30 large earthquakes (greater than magnitude 5) that have been felt within state lines in Washington in the past 150 years or so, since we have developed more abundant written records (which scientists call ‘historical’ earthquakes).

Earthquakes From Oral History

We also know about older earthquakes and tsunamis thanks to rich oral histories from Native American tribes. These tribes have lived in the Pacific Northwest since time immemorial, and their stories have helped present-day scientists better understand how frequent earthquakes are in Washington, and what kind of hazards we might expect from future earthquakes.

Scientists used the stories from tribes along the entire Pacific Northwest coast as a line of evidence that the last large earthquake on the Cascadia subduction zone was about 1700 CE. This date corroborated records in Japan of an ‘orphan’ tsunami and correlates with other features showing evidence of a large earthquake in the geologic record.

Stories from tribes near Seattle have also helped us to learn that the last earthquake on the Seattle fault occurred in the winter of 923–924 CE. This earthquake caused parts of Restoration Point on Bainbridge Island to be lifted 23 feet straight up.

This movement created a tsunami in Puget Sound and triggered a large landslide into Lake Washington. When the landslide hit the water it may have also created a tsunami in the lake. Cosmogenic dating, tree ring analysis and trenching have recently narrowed the year of this earthquake to 923–924 CE.

The Three Types of Tectonic Earthquakes in Washington

 Earthquake scientists often group earthquakes based on where in the Earth they occur. This kind of grouping gives us information about how frequently different kinds of earthquakes might happen and how large of an area may be affected by high intensity shaking. The deeper the fault that creates an earthquake, the lower the maximum shaking intensity possible, because the earthquake is further away from the surface and earthquake energy dissipates with depth as well as distance (read more about earthquake intensity). Throughout the world, ‘shallow crustal’ earthquakes generally refers to earthquakes that are less than ~45 miles (or 70 km) deep, so they happen within tectonic plates at the surface of the Earth. In the Pacific Northwest, the North American plate is not very thick, therefore, our shallow crustal earthquakes generally occur at depths less than 22 miles (or 35 km). Globally, many earthquakes still occur between depths of 45 and 200 miles, or even deeper. These earthquakes happen within plates that are sinking into the interior of the earth and here we call them ‘deep’ earthquakes. Earthquakes generally can’t occur deeper than about 430 miles (or 700 km), because this is the depth at which even the strongest rocks transition from behaving rigidly (prone to breaking like glass, able to produce earthquakes) to behaving plastically (prone to bending or flowing like silly putty, unable to produce an earthquake). This rigid-to-plastic change happens because rocks get hotter the deeper you go inside the earth, and hotter rocks are softer and deform more easily.

Check out the video below from IRIS for more about the three types of earthquakes in the Pacific Northwest.

Crustal Earthquakes

Though shallow earthquakes globally can be as deep as 45 miles (70 km), shallow crustal faults in Washington produce earthquakes predominantly in the upper 15 miles (25 kilometers) of the Earth’s crust. These types of faults exist in many areas of Washington State. Some are short in length (< ~2 km or 1.25 mi), and are thus incapable of producing a large magnitude earthquake that would result in severe shaking intensity. But there are longer crustal faults, such as the Seattle fault and the Southern Whidbey Island fault zone, that are long enough to produce large earthquakes up to magnitude ~7.5. Shaking from earthquakes on shallow crustal faults can be severe (MMI VIII) near the fault itself, even for an earthquake of moderate magnitude (around magnitude 6.5), because the fault is so close to (or even at) the surface of the Earth. Damaging earthquakes on shallow crustal faults are relatively common in Washington’s geologic history with two occurring in the 20^th century (the 1936 M_w 6.0 State Line earthquake and the 1872 magnitude 6.8 Entiat/Chelan earthquake). Shallow crustal faults can cause significant damage from shaking, and also from rupturing the ground surface, potentially breaking roads, bridges, pipelines and other infrastructure. Additionally, some of these shallow faults cross Puget Sound and thus are capable of producing a tsunami by displacing the seafloor by a sufficient amount.

Washington crust also hosts special types of earthquakes correlated with activity at Washington’s many active volcanoes. These earthquakes happen at or near a volcano. A wide range of processes can cause volcanic earthquakes, including magma movement in the subsurface, the movement of geothermally heated fluids, or changing stress in the Earth due to the dynamic nature of volcanic areas. A good example of earthquakes due to the effects of fluids is northwest of Mt. St. Helens in the St. Helens seismic zone. Earthquakes associated with volcanic activity tend to be overall smaller magnitude than earthquakes due to crustal faults described above. Large magnitude volcanic earthquakes are historically associated with major volcanic activity, such as with the landslide that initiated the major eruption of Mt. St. Helens in 1980. For more information about Washington’s volcano-related earthquakes, visit the Cascades Volcano Observatory web site.

Deep Earthquakes

Faults that produce deep earthquakes occur within the down-going plate of a subduction zone. In Washington, this is the Juan de Fuca plate, which produces earthquakes underneath western Washington. As the Juan de Fuca plate sinks, it experiences a lot of stress, bending and breaking during its journey deep into the Earth. The 2001 magnitude 6.8 Nisqually earthquake happened on a fault in the down-going Juan de Fuca plate at a depth of 32 miles (52 km). Magnitude 5+ earthquakes at this depth are frequent in Washington, with several occurring in the last century. Because they are so deep, the peak MMI intensity for these earthquakes is lower than for the same magnitude earthquake on a shallow crustal fault (peak MMI for the Nisqually earthquake was between VI and VII).

Subduction Megathrust Earthquakes

A subduction zone megathrust is the fault which serves as the tectonic plate boundary between the upper and lower plates in a subduction zone. In Cascadia, this is the fault along which the Juan de Fuca plate slides underneath the North American plate. These faults can be very long (Cascadia’s is more than 800 km or 500 miles long!), so they can produce very large magnitude or ‘mega’ earthquakes (greater than magnitude 8). The ground shaking from these earthquakes can last for a few minutes. The 2004 9.1M Sumatra-Andaman earthquake was a megathrust earthquake off the coast of Indonesia and had the longest fault rupture ever observed (~750 miles miles or ~1,300 kilometers) and the longest duration of faulting (at least 10 minutes). The 2011 magnitude 9.1 Tohoku earthquake in Japan occurred on this type of fault and released enough energy to slightly change the Earth’s axis of rotation. Additionally, because the shallowest part of these faults are underneath the ocean, large amounts of seawater can be displaced during the earthquake and cause damaging tsunamis. The most recent earthquake on the Cascadia subduction zone happened over 300 years ago on January 26, 1700, with an estimated magnitude of ~magnitude 9. We know this date precisely due to records maintained by Samurai communities in Japan at that time (read this fascinating story of scientific detective work in The Orphan Tsunami of 1700). These earthquakes happen every few hundred years on average. Because megathrust earthquake magnitude can be so large, peak MMI shaking intensity for the next event could be severe (MMI VIII) in western Washington.

 

Geologic Hazards Associated with Major Earthquakes

Earthquakes can be the underlying cause for many different types of geologic hazards. This section details these different hazards to help people understand the varied consequences of an earthquake occurrence. Read the sections below to understand the connection between earthquakes and their associated hazards, which can prepare you to respond safely during the next earthquake and to ask useful questions about the safety of where you live and work in the event of a strong earthquake.

Ground Shaking

Earthquake waves move the ground surface up and down and side-to-side during an earthquake. For very large earthquakes with the highest shaking intensity, this movement is so fast that accelerations can reach values higher than Earth’s gravity. This means these waves can throw things into the air. Most earthquakes will not create high intensity shaking, but many can result in significant ground movement that can topple unsecured furniture, damage vulnerable structures, and break utility lines. Ground shaking is more hazardous in areas of higher earthquake intensity, such as near the epicenter of an earthquake and also in areas farther from the fault where amplification of earthquake wave energy occurs due to the local rock and soil conditions.  As an example, parts of Seattle and certain areas of downtown Olympia are built on softer ground that amplified ground shaking during the Nisqually earthquake in 2001. Some buildings in these areas were damaged, while similar buildings in areas nearby built on harder ground were not.

Seismic waves are amplified or damped when traveling through different geologic materials. The figure below shows the National Earthquake Hazard Research Program (NEHRP) Site Classification system (labels A, B, BC, etc.) that predict the degree to which near surface materials like soil or bedrock may amplify or dampen shaking during an earthquake. In general, loose soils like sand will experience extreme shaking, while sites underlain by rock (called bedrock) will experience less shaking in an earthquake. The WGS School Seismic Safety Program uses geophysics to determine these site conditions at Washington Schools.

Geologists and geophysicists at the Washington Geological Survey map out the geology at the surface and just under the surface to identify areas where earthquake shaking could be amplified. This gives citizens of Washington the information they need for taking action to reduce damage during an earthquake. Read more on our School Seismic Safety Program webpage.

 Fault Rupture versus Ground Failure  

 When earthquakes occur on faults that reach the Earth’s surface, the ground may rupture. This occurs when an earthquake that is large magnitude has fault displacement that extends upward to the ground surface. These are primary effects of the earthquake.

Depending on the type of fault, the ground can move laterally, vertically, or a combination of both. When the fault itself ruptures the surface and creates offset, or displacement, it is called a ‘fault scarp’. Sometimes geologists can use the offset land surface to understand how much the fault moved during the earthquake.

Ground failures can also result from earthquakes when unstable land shifts during ground shaking. Ground failures are caused by shaking that destabilizes slopes and sediments near the surface, these are secondary effects of earthquakes. Secondary effects are failures caused by shaking and include liquefaction and lateral spread (cracks in the ground), coseismic landslides and rock failures. The deep magnitude ~7 April 1949 Tacoma earthquake caused damage from southern Oregon to British Columbia. In Seattle, ground shaking from the earthquake damaged buildings, weakened bridges, started fires, and caused ground failure like cracks in the surface. One of these cracks appeared along the pathway around Green Lake in Seattle (see picture below).

Liquefaction

Liquefaction happens when wet soil or sediment loses strength during shaking from an earthquake. The material becomes so weak that it behaves more like a liquid than a solid, like when you wiggle your toes in the hard wet sand at the beach and then they sink. Liquefaction has caused significant damage during earthquakes in Washington.

Many low-lying areas (such as river valleys, deltas, tidal estuaries, and man-made fill) have wet soil or sediment beneath them that could liquefy during earthquakes. When this happens, even a very shallow slope can cause the ground to slide. Some parts of major cities (including Seattle, Tacoma, and Olympia) are built on land that was ‘reclaimed’ from soft and wet tidal ocean areas by adding man-made fill. If not properly engineered, areas like these can be susceptible to liquefaction.

Earthquake-Triggered Landslides

Landslides can be caused by strong ground shaking during an earthquake. This kind of landslide is called an earthquake-triggered landslide. When the ground shakes during an earthquake, it moves up and down, and side-to-side, acting like ‘additional’ gravity. This can cause landslides to occur.

In Washington, the risk from earthquake-induced landslides is large due to prolonged and intense rainfall, rain-on-snow events, unstable glacial and volcanic soils, and steep coastal bluffs. Many landslide-prone areas of Washington are also located near active faults. The 1949 deep earthquake near Tacoma triggered a landslide near the Tacoma Narrows that caused a local tsunami. Even places that are far from active faults are still at risk of having landslides during a large Cascadia subduction zone earthquake. Learn about at-risk areas on our Landslides page and visit our Geologic Information portal which has map information about landslide susceptibility.  Have a plan in place to mitigate your risk if you live in an area prone to landslides.

Tsunamis

A tsunami is a sea wave of local (within or near to Washington) or distant (such as from Alaska or Japan) origin that results from large-scale seafloor displacements associated with large earthquakes, major submarine slides, or even exploding volcanic islands. Tsunamis can be created from multiple phenomena, but are most commonly produced from earthquakes that move the ocean floor vertically. Because of this, tsunamis primarily originate from subduction zone faults. The last large tsunami originating from Cascadia was the subduction zone megathrust rupture in 1700. Scientists have evidence that it devastated the coast of the Pacific Northwest and traveled to Japan. It was also recorded by local people in both the Pacific Northwest (through oral tradition) and Japan (written records on the samurai). Another large earthquake in Alaska in 1964 created a tsunami that spread to the west coast of the U.S. and resulted in extensive damage and numerous casualties. Tsunamis can also be triggered by large landslides that displace seawater during earthquake shaking.

Visit the WGS tsunamis webpage to learn about tsunami hazards, preparedness, and evacuation.

Seiches

A seiche (pronounced: saysh) is the sloshing of a closed body of water from earthquake shaking. In effect, the wave energy is ‘trapped’ by the edges of the body of water. This can happen in a lake, pond, or even a swimming pool. The body of water has to be just the right size, shape and distance away from the earthquake to concentrate the energy into a standing wave.

Aftershocks

Aftershocks are additional earthquakes that occur after a large earthquake (the ‘mainshock’). Aftershocks are smaller than the mainshock, but they can still be damaging. The aftershocks won’t necessarily occur along the same fault that the mainshock ruptured, though they can, but they may also occur along other faults in the same general vicinity (usually one to two fault rupture lengths away). Depending on the size, type, and location of the earthquake (deep earthquakes are less likely to cause aftershocks than shallow earthquakes), aftershocks can last for weeks to years following the main shock. The 2011 Tohoku magnitude 9.1 earthquake that struck Japan was a mainshock. It was followed by thousands of aftershocks in the weeks and years following the event, some as large as a magnitude 7.7; there was even an magnitude 7.1 aftershock on February 13^th, 2021, ten years after the mainshock.

 You can find aftershock information for current and historic earthquakes on the USGS Aftershock Forecast website.

How to Assess Your Personal Earthquake Risk

Future earthquakes could happen anywhere in Washington. Earthquake scientists have prepared, and continue to improve, products that can help Washington’s citizens live as safely as possible in earthquake country. Read this section to obtain straightforward explanations of earthquake maps and data that can help you plan how to be safe where you live and work. This information should be useful for any Washington citizen who wants to learn how to use WGS and federal earthquake data to help improve their safety in the places they spend time, such as current or future residence, workplace, driving routes or other locations.

Where Could the Next Damaging Earthquake Happen?

Large and damaging earthquakes are inevitable in Washington, but no one knows exactly where and when they will happen next. Scientists cannot predict earthquakes. What scientists can do is attempt to understand the future hazard for areas that are prone to earthquakes by studying and mapping active faults and learning from historic earthquake events. Citizens can then use this information to develop an expectation about where it is more or less likely that a damaging earthquake could occur.

Active Faults in Washington

Washington State has hundreds of faults that we know or suspect are active. Some of these faults are in remote areas and others cross under major cities and pose a significant risk to our communities. The WGS geologic information portal has the most up-to-date map of these active faults.

The largest fault affecting Washington: The Cascadia subduction megathrust

The largest active fault that will one day affect Washington (and the whole Pacific Northwest) is the Cascadia subduction zone. This fault is offshore and extends from Northern California (near Mendocino) to Vancouver Island. The Cascadia megathrust last ruptured over 300 years ago with an estimated magnitude of 9. This fault may also produce moderate magnitude earthquakes (magnitude 5+). Damaging earthquakes are inevitable on this fault, but we do not know exactly when they will happen. See the “When could the next damaging earthquake happen?” section for more information on how often scientists think earthquakes happen on this zone.

Faults in the down-going Juan de Fuca plate

These unnamed faults produce deep earthquakes. Though the peak shaking intensity is lower for these earthquakes than for earthquakes from other faults, movement of these faults is frequent, with more than one M5+, potentially damaging earthquakes happening in a century. See the Historic Earthquakes in Washington Storymap to see the locations and magnitudes of such earthquakes in Washington history. The most recent example of one of these deep earthquakes is the 2001 Mw 6.8 Nisqually earthquake.

Seattle fault

The Seattle fault last ruptured about 1,100 years ago in about 900 AD with a magnitude ~7.0-7.5 earthquake. This fault is underneath several major Puget Lowland urban areas including Bremerton, West Seattle, and Bellevue. Though geologists know that this fault is active, we do not have a good estimate for how often earthquakes happen on this fault. This fault likely connects to the Saddle Mountain West fault zone (), and they may interact to create complex ruptures.

North Olympic fault zone

The Lake Creek-Boundary Creek fault and the newly-mapped and studied Sadie Creek fault (work is still ongoing as of 2022) together form the North Olympic fault zone. This ~35 mi (~60 km) long active fault trends east-west along the northern edge of the Olympic Peninsula, ~5 mi (~8 km) south of Port Angeles. Geologic and geomorphic studies (many are of offset steam channels and fault scarps) indicate this is a predominantly right-lateral strike-slip fault. It helps accommodate shortening of the crust in the north-south direction across the Olympic Peninsula as well as accumulated stresses from the Juan de Fuca subduction zone. Recent work provides evidence of 3-5 earthquakes on this fault zone since the retreat of the Juan de Fuca glacial lobe ~14,000 years ago (Duckworth and others, 2021). This evidence also shows some of these earthquakes ruptured long segments producing magnitude 7.0-7.5 earthquakes.

Southern Whidbey Island fault zone

The Southern Whidbey Island fault zone (SWIF) trends northwest across the southern part of Whidbey Island to merge with the west-trending Devils Mountain fault zone south of Victoria, Canada. Southeast of Whidbey Island, the SWIF likely connects with the Rattlesnake Mountain fault zone near Maltby, WA, forming one, long (~120 mi or ~190 km), continuous set of interconnected faults. This fault zone accommodates components of both right-lateral strike-slip and reverse faulting due to the north-south compression of the Puget Lowland region. One of the strands in this fault zone created an approximately magnitude 7 earthquake around 3,000 years ago and four to eight earthquakes between magnitudes 6 and 7 since glacial retreat in this area ~16,400 years ago (Sherrod and others, 2008).

Wallula fault

The Wallula and associated faults (collectively called the Wallula fault zone) extend ~65 miles (over 100 km) from the Rattlesnake Hills, through the Tri-Cities and across the border into Oregon just south of Touchet, WA. It is important because scientists think the 1936 magnitude 6.1 State Line earthquake likely occurred on this fault (Brocher and others, 2018). During this earthquake, the highest shaking intensity was felt near Freewater, OR, but higher intensity was also recorded in Washington. This fault has been under intensive study by U.S. Geological Survey scientists since 2018 with multiple trenches planned.

Spencer Canyon fault

The Spencer Canyon fault crosses highway 97 between Chelan and Wentachee. The combined length of the fault and its associated northeast-trending fold is ~45 miles (~70 km). An approximately magnitude 6.8 earthquake on December 15, 1872, near Lake Chelan in Washington State is recognized as the largest shallow earthquake in the Pacific Northwest in the last ~150 years, and has only recently been closely studied. The earthquake was broadly felt but the lack of recognized surface deformation caused confusion as to the earthquake's location. New Lidar data analyzed and published in 2021 revealed a NW-side-up scarp along a NE-trending fault on the north side of Spencer Canyon near Entiat, Washington (Sherrod and others, 2021). They used trenching, radiocarbon dating, and tree ring counts to determine if this scarp and nearby landslides were related to the 1872 earthquake. Their studies show that the scarp was formed during the last fault movement between 1856 and 1873 CE. From these observations they infer 1872 Lake Chelan earthquake happened due to movement along this fault.

When Could the Next Damaging Earthquake Happen?

Scientists in the United States have been intensively studying earthquakes and active faults for well over 100 years (since the 1906 San Francisco earthquake showed their potential for major impact on modern infrastructure). But they cannot yet predict when a fault will generate an earthquake (for example, saying an earthquake of a specific magnitude will happen on a specific day on a specific fault). However, scientists can learn which faults are active and which are inactive which is helpful information to have, and in some instances, they can find enough evidence for when past earthquakes occurred on those faults to build an earthquake ‘forecast’. See the section on Earthquake Forecasts to read more about this process. Even if there isn’t enough information to make a forecast, knowing how often large earthquakes have happened in the past can provide insight into how and why earthquakes happen, and can give a sense for how often earthquakes might occur in the future.

Deep Earthquakes

The most frequent earthquakes in Washington are deep earthquakes. Each century, we should expect more than one magnitude 5.5+ potentially damaging earthquake to happen within the down-going Juan de Fuca plate. In the last century, there have been at least six deep earthquakes above a magnitude of 5. The most recent damaging earthquake in Washington—the 2001 magnitude 6.8 Nisqually earthquake—was of this type.

Subduction Megathrust Earthquakes

You’ve likely heard about subduction megathrust earthquakes in the press. Because they have the potential to produce such large magnitude earthquakes (magnitude 9), scientists spend a lot of time studying them. Unfortunately, there is a lot still left to learn. Some geologic records that could tell us more have not yet been examined, and scientists are still deciphering and discussing the meaning of geologic records found so far. Since earthquakes on the Cascadia subduction zone are still an area of active research, the public should expect that the information shared about these earthquakes will be updated and revised over time to reflect the current state of scientific consensus. It is good to remember, each time the story changes, it becomes slightly more accurate and detailed, thus improving over time.

The last major subduction megathrust earthquake was over 300 years ago in the year 1700, and it was approximately magnitude 9. Such a large earthquake would only be produced by movement along most of the fault surface, which scientists call a ‘full margin rupture’.

Scientists have determined how often full margin earthquakes happen by using sediment records obtained by drilling into the continental shelf offshore of North America. The interpretation of these records is still ongoing, but the records generally suggest that full margin ruptures occur every ~500 years. Evidence obtained from onshore sedimentary deposits has generally agreed with the offshore record, but recent work uncovered more past earthquakes, increasing the frequency of earthquakes to every ~400 years.

It is important to note that these estimates of earthquake frequencies are averages. Many earthquakes identified in the sedimentary deposits are ‘clustered’ in time, meaning that some of the earthquakes happened shortly after another earthquake (such earthquakes were only separated in time by around 50 years), and some of the earthquakes occurred hundreds of years after the previous earthquake (the longest gap identified was 850 years elapsed between earthquakes). This means that there is large variability in the time between earthquakes.

In addition, not every megathrust earthquake is a full margin rupture. In fact, there is good evidence that ‘partial ruptures’ happen at both the northern and southern ends of the subduction zone. During partial ruptures, only part of the megathrust moves, creating an earthquake closer to magnitude 8 or even a bit smaller. Though these earthquakes are smaller than the full margin ruptures, they could still create shaking, damage and possibly a tsunami in Washington. Given the uncertainties, both scientists and citizens should prepare for strong shaking in western Washington from an earthquake on this fault zone any time between tomorrow and 500 years from now!

Crustal Earthquakes

Faults within the North American plate under our cities and towns can also create dangerous earthquakes. Though the highest magnitudes probable (~7.0–7.5) are lower than for the subduction megathrust earthquakes, they are so close to the surface of the Earth under our communities that they can create very high intensity shaking close to the fault. Luckily, each fault generally produces an earthquake infrequently (on the order of every 1,000–10,000 years), but this can make it difficult to know how concerned we should be about them. In addition, if there are multiple active faults that could create shaking in any given area, then the chance for damaging shaking in that spot is greater than if there were only one active fault close by.

Earthquake Forecasts

At present, the optimum state of knowledge scientists have reached in places with frequent crustal earthquakes (like California) allow scientists to produce an earthquake ‘forecast’ for a specific region that contains active crustal faults. To do this, scientists need to understand how often earthquakes that could produce intense shaking within an area happen on particular faults.  They also need to know what a typical magnitude is for those faults. These forecasts are much like the weather forecasts meteorologists produce to give us an idea of what the weather will be like on any given day for a region. Like weather forecasts, earthquake forecasts apply only to a specific region over a set range of time and for earthquakes above a specific magnitude. For example, as of 2022, there is a 72% chance that a magnitude 6.7 earthquake will happen in the San Francisco Bay Area over the next 30 years (USGS earthquake forecasts for California). Meteorologists have much more data at their disposal to help them forecast the weather than seismologists have to forecast earthquakes, even in areas with the most complete data.  Therefore, earthquake forecasts are much less detailed than weather forecasts.

Scientists are just starting to make earthquake forecasts for Washington. We would like to have forecasts covering all active faults that could cause shaking in  Washington (for example the Seattle metro area, or the Tri-Cities).

U.S. Geological Survey scientists have made the first earthquake forecasts for western Washington. As of 2025 in the Puget Sound region, there is an 85% chance of at least a magnitude 6.5 deep earthquake in the Puget Sound region in the next 50 years. In the same time frame, there is a 15% chance of a magnitude 9 subduction megathrust earthquake and a 17% chance of a at least a magnitude 6.5 shallow crustal earthquake in the Puget Sound area.

Seismic Risk Resources

It is important for the best possible safety of every citizen within Washington for each person or family to learn about the seismic hazard and risk for where they live and work. Then they can take appropriate action to be prepared for the next damaging earthquake. 

Seismic (or earthquake) risk is a little different from seismic hazard. Seismic hazards are naturally occurring phenomena capable of causing loss or damage. Risk is the potential that exposure to the hazard will lead to a negative consequence such as loss of life, injury or economic loss. While a person can’t change the underlying seismic hazard for where they live, work, and travel, they can reduce their earthquake risk by managing their built environment (including such things as retrofitting buildings, securing heavy or precariously placed objects and packing enough supplies to be autonomous when they travel), mentally preparing for shaking, and knowing/practicing what to do during and after shaking. Understanding what steps to take to make the environment where you live safer involves understanding both your hazard and risk. Areas where you live, work and travel may each have different specific earthquake hazards affecting them – understanding each of these hazards is important as you think through and plan for an earthquake scenario. Determining your risk may require inquiring with your employer, landlord or city officials about structures you spend time in (for example your house, apartment, office building or even bridges you might cross) to find out how seismically safe they are. This section outlines different ways to understand your seismic hazard. Scientists at the Washington Geological Survey spend time researching, revising and translating the best available science and current knowledge for the public. See the section on Ensuring Home Safety for information on taking action to reduce your risk given the seismic hazards in your area, which includes links to other agencies’ information who dedicate a lot of their time and effort to reducing earthquake risk.

Seismic ShakeMaps and Scenarios

Scientists generate earthquake scenarios to model shaking and damage areas for potential future earthquakes; these scenarios are based on past earthquakes and hypothetical earthquakes along known active faults. A damaging earthquake is typically greater than magnitude 5.5, and damage could include loss of life, injury, or damage to our built environment. The scenarios are good for preparing for the next earthquake (also known as hazard mitigation planning) because they answer two questions: first, how much shaking could we expect in any given location from this/these scenarios? Second, given that amount of shaking, with the current physical distribution of people and community resources, how bad would the damage be? A scenario is not a prediction or forecast; it does not tell us when or where an earthquake will happen. What it does tell us is what outcome we could expect if a particular earthquake were to happen. Generating an earthquake scenario requires creating a ShakeMap which shows the intensity of shaking (on the Modified Mercalli Index scale or MMI) that a particular earthquake would produce. The intensity of shaking depends on such factors as how far away a place is from the fault rupture, what sort of geology is at the surface in that place, and other characteristics of the physical process of how the rupture happens. In order to estimate loss (physical, economic, and social) from a scenario model earthquake, scientists and practitioners use FEMA’s HAZUS modeling process to pair the ShakeMap with current population distribution, infrastructure and building information, as well as social demographics. This creates a forecast of damage and loss due to the model earthquake.

The 2010 Washington State Seismic Scenarios

The Earthquake Hazards Scenario Catalog contains loss estimates for a suite of earthquake scenarios. The resources include a list of scenario model earthquakes, downloadable GIS-compatible layers for viewing the associated ShakeMaps, and downloadable HAZUS reports and scenario summary reports. The scenarios web page also explains how a scenario is created, which is useful for understanding the benefits and limitations of any given scenario. These scenarios were selected to represent reasonable estimates of the most serious earthquake hazards everywhere in Washington as a basis for planning. As of 2026, the U.S. Geological Survey has created ShakeMaps and FEMA contracted HAZUS data for a set of shallow crustal faults in Washington state that have been updated and revised since 2010. WGS researchers are in the process of creating new scenario summary reports and other products from this new analysis. If you want to know which faults are near where you live that could potentially produce a damaging earthquake, refer to our active faults map layer on the portal.

National Seismic Hazard Maps

Another way for citizens and officials to assess their seismic hazard is by viewing the U.S. Geological Survey National Seismic Hazard Map for their region. A seismic hazard map is similar to a seismic scenario in that it is not a prediction. It does not tell you when or where an earthquake will happen. However, it is a type of earthquake forecast. Current U.S. Geological survey practice will update the National Seismic Hazard Map on average every four years and each update will incorporate the most up to date understanding of the seismic hazard. This map is the basis for national, state and local building codes and is applied to design for new construction. The map also contributes to insurance rate structures, assessment of public earthquake risk and other public policy. This section describes what seismic hazard maps are, how to understand them, and where to find them.

What is a seismic hazard map?

A seismic hazard map shows a compiled version of hazard from all well-understood faults that could produce an earthquake in a region. A hazard map is probabilistic; it shows, based on the most reliable and current information, how often damaging shaking is likely to affect a particular location. Scientists produce them for MMI level VI (strong earthquake felt by all people in an area) or higher. Therefore it is not a ShakeMap, but scientists use ShakeMaps associated with seismic scenarios as input to make a seismic hazard map. The colors on a hazard map let you compare hazard for different areas within a region. The U.S. Geological Survey explains further: “Areas with the same color on the map should expect a similar number of occurrences of damaging earthquake shaking. However, the level of damage caused by the ground shaking associated with each earthquake could be very different. For example, a smaller earthquake that produces some damage over a smaller area, and a larger earthquake that causes widespread damage, are both counted in occurrences of damaging earthquake shaking.”

In the current long-term seismic hazard map for the U.S., hot colors (red, orange, yellow) indicate a greater likelihood of damaging earthquakes in the next 50 years. However, the U.S. Geological Survey emphasizes, “There is a chance of damaging shaking anywhere and everywhere in the United States. Most people pay particular attention to areas with the hottest colors. True, these areas will most often have damaging shaking, but don't ignore the cooler shades. Damaging shaking can and will happen in those areas, too, but less often. In fact, damaging shaking is possible in all fifty states. The cooler color areas, like grey, are low hazard but not no hazard.”

How do Scientists Make a Seismic Hazard Map?

Scientists compile geographic, historical, and geologic data to create a hazard map. This information includes known active faults (including earthquake history on those faults), stand-ins (proxies) for unknown earthquake sources, past histories of small earthquakes, shaking measurements from past earthquakes, modeled movement from hypothetical earthquakes (ShakeMaps), high-precision measurements of crustal movements from GPS data, and the geology of the region in question. Scientists use all of this information to compute the potential to exceed a chosen ground motion over a particular period of time. For the U.S. Geological survey National Seismic Hazard Model, it is an MMI level VI over 50 years. Hundreds of thousands of evenly spaced computations across the map area receive these estimations and the results are summarized into a series of maps including the probabilistic map shown here. Other maps come out of this process that are more useful for engineering geologists and people updating earthquake provisions in building codes. Visit the USGS FAQ site on the National Seismic Hazard Map for additional details.

Where Can I Find the Most Recent National Seismic Hazard Map?

All regions of Washington have some seismic hazard from a moderate (eastern parts of the state) to high (closer to the coast) level. To see the general hazard in your part of the state, visit the U.S. Geological Survey web site to view the latest version (completed in 2023). There are several versions of this map and depending on what the intended use is one, or many, could fit your needs. The most commonly used map is the US long-term map with a 2% chance of exceedance in 50 years assuming site class D; consult with an engineer or the USGS if you are unsure which version of the map to use.

Prepare Yourself for Earthquakes

Everyone in Washington should prepare for the event of an earthquake, regardless of your risk.  However, knowing your risk can help improve your preparations. Realize that living in a higher risk zone isn’t the end of the world. Even people living in the riskiest zones can take steps to prepare their homes and family safely get through the next earthquake. This next section is focused on your home, but examining information for all locations where you spend time (work, school, driving routes, vacation spots) is important because it’s impossible to know exactly where you will be during the next earthquake.

Ensuring Home Safety

Everyone in Washington should prepare for the event of an earthquake, regardless of your risk.  However, knowing your risk can help improve your preparations. Realize that living in a higher risk zone isn’t the end of the world. Even people living in the riskiest zones can take steps to prepare their homes and family safely get through the next earthquake. This next section is focused on your home, but examining information for all locations where you spend time (work, school, driving routes, vacation spots) is important because it’s impossible to know exactly where you will be during the next earthquake.

Know Your Hazards

There are many tools available to help you investigate seismic hazards that might affect the place you live. The rest of this website contains many sections that can help you understand the resources described in this section. As referenced specifically in the sections below, please visit our Geologic Information Portal for the most up-to-date WGS earthquake hazards map products. Our Geologic Hazard Maps page has the most up-to-date listing of all of our stand-alone hazard map publications. If you are not sure what hazards might affect where you live, see our Emergency Preparedness Page for step-by-step investigations that can help you get the total picture of potential hazards in your area.

Consider and Address Your Risk

Consider where you live as well as all the places you spend time such as at work, at school and during daily driving. Pay special attention to bridges you must cross during travel and don’t forget travel you might undertake outside of your daily pattern to other parts of the state. Have you found any hazards in the places you spend time? Below we list some recommendations for what to do to lower your risk for a number of hazards you might have identified through reviewing the maps and resources listed above.

• Do you live close to an active fault? Take higher precautions to protect your home and belongings from strong shaking.  Look closely at the ShakeMaps to estimate the modeled MMI level of shaking and prepare your home for the kind shaking described for that category in the MMI scale. Preparing includes structural (for example foundation) retrofits or may simply include securing your belongings in your home so they don’t fall, break or cause injury. Download the WGS Homeowner’s Guide to Earthquakes for more specific information to get you thinking about ways to secure your home.
• Do you live in an area prone to liquefaction? Recommendations above for living near an active fault apply to you too. If you are unsure about the foundation of your home, you may want to consult a geological engineer. Another source of information about the stability of your home (especially if you live in a home like an apartment complex), is your local city or county building officials. They may be able to tell you about permits filed for the construction of your dwelling and about what is required for builders locally with regards to earthquake-safe construction.
• Do you live in an area prone to landslides? Familiarize yourself with landslides on the WGS Landslides web page, especially the section ‘Reduce Your Risk.’ WGS also has a downloadable Homeowner’s Guide to Landslides. If you are unsure about your risk or how to address your risk, you can also hire geological engineer to inspect your property and home.
• Do you live in a tsunami inundation zone? Make sure you have a plan for escape after the earthquake shaking stops.  Familiarize yourself with tsunamis on the WGS Tsunamis web page, especially the sections on ‘Preparation and Evacuation’ and ‘Tsunami Evacuation Maps.’ Find and download evacuation maps for your area and consult the ‘Tsunami Evacuation’ layer in the ‘Tsunamis’ section of the Geologic Information Portal. We also have a guide to Tsunami Hazards in Washington State.
• Consider buying earthquake insurance. Regular homeowners’ and renters’ policies do not include coverage for catastrophic events like earthquakes. Learn about the types of insurance available, what type to buy, and other information like what to ask your agent or broker when you inquire about earthquake insurance on the ‘Insure Against Earthquakes’ web page (put together by the non-profit Cascadia Region Earthquake Workgroup).

Earthquake Early Warning

During an earthquake, a rupturing fault makes several different kinds of waves that send energy away from the epicenter, like ripples on a pond. The fastest-moving seismic waves (primary or P-waves) travel about 3.7 miles per second in rock and generally do not produce strong shaking. P-waves are followed by slower moving, more damaging waves (including both secondary or S-waves and surface waves) that travel about 2.5 miles per second. The speeds of today’s data telecommunications systems are many times faster than these seismic waves. All of these wave speed factors make it possible for alerts to reach people after the earthquake has happened, providing precious seconds to minutes before strong shaking arrives.

The U.S. Geological Survey’s ShakeAlert seismic network consists of seismic wave detection instruments (seismometers) strategically placed across the states of Washington, Oregon, and California. These instruments detect the first arrival of the P-wave and immediately transmit data to a ShakeAlert processing center, which estimates the location, size, and expected shaking from the quake. The goal of this system is to send out a ShakeAlert-generated message, also called an earthquake early warning, to individuals and communities before damaging shaking arrives.

The U.S. Geological Survey maintains a threshold for the predicted amount of shaking calculated by the automated system. If that threshold is met or exceeded, an emergency alert is then sent to Technical Partners, who deliver alerts through automated systems to their customers. This is the USGS ShakeAlert earthquake early warning system.

The point of ShakeAlert is to provide seconds of advanced warning before damaging earthquake waves arrive, providing enough time for people to take a protective action, such as DROP, COVER, AND HOLD ON, and time for automated systems to respond (things like the automatic slowing of trains, elevators stopping and opening doors at the nearest floor, and the automated closing of valves to protect water systems). For more information about ShakeAlert, visit the U.S. Geological Survey ShakeAlert website and the official ShakeAlert website, and to make sure you have emergency alerting enabled on your cellular device, visit the Washington Emergency Management Division website.

What to do before, during, and after an earthquake 

The most important thing you can do before the next earthquake is to understand your risk and prepare. For a more visual representation of these steps, see the ‘What to Expect in a Big Urban Earthquake' storymap.

Before an Earthquake

• Assess your seismic risk risk (see How can I find out my Seismic Risk? section).
• Know what to expect during and after an earthquake. The Washington Emergency Management Division has a video on earthquake preparedness. 
• Practice your reaction during an earthquake. Participate in the yearly Great ShakeOut earthquake drills. These drills occur on the 3rd Thursday of every October. They are a great way to practice what to do when an earthquake happens.
• Make sure your phone is ready to receive ShakeAlert earthquake early warning messages.
• Prepare to be on your own for at least two weeks following an earthquake. Having an emergency response plan for you and your family is a good start, as is identifying and securing items in your home or work that could cause damage. Be 2 Weeks Ready by preparing a kit of essential supplies (food, water, medicine, pet supplies, etc.) you will need if regular societal services are disrupted.
• Look into getting earthquake insurance coverage for your dwelling. The Cascadia Regional Earthquake Workgroup website has more information.

During an Earthquake

Drop to your hands and knees. Cover your head and neck with your arms to protect against falling debris. Hold on to any sturdy shelter until the shaking stops.

Check the WGS emergency preparedness page for more information about what to do during an earthquake and how to prepare. There is also a video from IRIS that describes what to do during an earthquake.

After an Earthquake

Once the shaking has stopped, exit the building if it is safe to do so. Evacuate to higher ground if you are near a large body of water. Tsunamis are a common result of large earthquakes in Washington. Expect aftershocks. After a large earthquake it is common to have other large earthquakes for hours, days, and even weeks. Drop, Cover, and Hold On whenever you feel shaking. Check yourself and those around you for injuries. Expect fires and help to extinguish them. Small fires are the most common hazard after an earthquake. Never use a lighter or match near damaged areas because of the risk of gas leaks.

Visit our Emergency Preparedness Page for more details on how to get ready for the next geologic hazard that will happen in Washington.

Prepare your kids for earthquakes

Rocket’s Rules!

Watch Rocket’s Rules for Safety dance video to learn how you can be ready for the next earthquake. The video is also available in Spanish and there is a fun activity/coloring book that can be found here.

The Extraordinary Voyage of Kamome

On April 7, 2013, a little over two years after a magnitude 9.0 earthquake triggered a massive tsunami off the coast of northeastern Japan, a lone boat washed up on the shores of Crescent City, California.  The boat belonged to a high school in Rikuzentakata.  This is the true story of a small boat that, through the efforts of a hardworking group of Crescent City students, forged friendships and brought hope to communities on both sides of the Pacific. Visit the Kamome web page to listen to or download the book. Watch the animated version below or in other languages at the Kamome web site.

ShakeOut With Your Kids

The Great ShakeOut is a great time to have some fun with your kids practicing Drop, Cover and Hold On.

An earthquake just happened and I want more information

The Washington Geological Survey and our state and federal partners publish earthquake information for consequential (think: greatly affecting society) earthquakes as soon as possible after they happen. This section contains links for where to find the most reliable and up-to-date scientific information.

• WGS Clearinghouse

• U.S. Geological Survey Latest Earthquakes Map

• U.S. Geological Survey “Did You Feel it?” Report an event you felt here.

• U.S. Geological Survey Aftershock Forecast

• Pacific Northwest Seismic Network

WGS Earthquake Data Products and Projects

Washington Geological Survey scientists, data managers, and editors work in many different areas of research, data collection and (or) archiving, and public outreach regarding earthquakes. This section contains brief descriptions of and links to earthquake and earthquake hazard publications and long-term earthquake-related projects of the Washington Geological Survey. If you are looking for specific data sets, maps, or publications we might have, this section may help you find it.

Finding and Learning About Faults

The Washington Geological Survey conducts and publishes geologic mapping to identify and characterize faults throughout the state. WGS scientists pair traditional geologic mapping methods with technological aids such as digital mapping tools, lidar, and geophysics to investigate fault extents, geometry in the subsurface, and past earthquake history.

You can view mapped active faults on the Geologic Information Portal. 

Archiving Active Fault Locations and Details

The publication Faults and Earthquakes in Washington State is a state-wide compilation of active faults and folds first published in 2014 as a digital map and now included in our Geologic Information Portal. Each year we map additional areas within the state at higher resolution to learn more about existing faults and (or) discover new ones, and update the Portal map with this information on a regular basis. The Geologic Information Portal is the best place to look for the most up-to-date maps of active faults in our state.

Washington All-Hazards Clearinghouse

Following a significant natural hazard event affecting our state (earthquake, tsunami, landslide, volcanic hazard), the Washington Geological Survey (WGS) will activate a post-event clearinghouse. The Geologic Hazards Clearinghouse will coordinate scientific data collection following certain natural disasters, and this data collection will include information on the geologic impacts and damages caused by the natural disaster. The information obtained through Clearinghouse efforts will be shared with disaster response teams, other scientists, and the public. In the event of an earthquake, WGS will coordinate with key partners who will also be doing such work (such as the Pacific Northwest Seismic Network, the U.S. Geological Survey and others) to make efficient use of time and resources for such efforts.  See our Geologic Hazards Clearinghouse page for more information.

Communicating Earthquake Hazards to the Public

The Survey works to increase public understanding of faults and earthquake hazards in our state. We work closely with agencies like the Washington State Emergency Management Division, the Washington Seismic Safety Subcommittee, the U.S. Geological Survey, the National Oceanic and Atmospheric Administration, and the Federal Emergency Management Agency to ensure that the best-available science is used in the development of hazard mitigation plans and communication with the public. Please contact our Geologic Planning Liaison for assistance if you are working on a hazard mitigation plan and/or incorporating geologic hazards into decision making.

Consider subscribing to our blog, Washington State Geology News, to receive notifications when new information is published. Also check out Ear to the Ground, published by the Department of Natural Resources.

If you would like help understanding our earthquake risk assessment products, to ask questions about how to assess your risk, or to request a presentation please contact us: Geology@dnr.wa.gov.

Assessing School Seismic Safety

The Washington Geological Survey is working with the Office of the Superintendent of Public Instruction (OSPI) to better understand and assess the seismic safety of school buildings across the state. Visit our School Seismic Safety page for more information.