From Ground Shaking to Tsunamis: Earthquake Hazards

Earthquakes pose several hazards to our natural and built environment. Different parts of Cascadia will experience different hazards. For example, during the 2001 Nisqually earthquake that shook the Puget Sound region, buildings crumbled, bridge supports cracked, and more than 400 people were injured. In coastal areas, a powerful offshore quake could trigger a tsunami, a series of massive waves that would flood the shoreline within minutes; damage or destroy roads, bridges and utility lines; and likely cause many injuries and deaths.

Tools are available to help you determine the hazards you may encounter. These include hazard maps at national, state and (in some cases) local scales that show the potential for ground shaking from future earthquakes. Learn more about earthquake hazards in your area.

Because Cascadia has a rich history of seismic activity, all residents and businesses should be familiar with and prepared for the primary hazards associated with earthquakes. These include ground shaking, landslides, liquefaction, and in some areas, tsunamis. 

These primary hazards often produce secondary hazards such as ruptured utility lines, hazardous spills, and fires. Buildings can crumble or collapse, trapping people inside and burying streets in rubble. Failed bridges can disrupt or cut off entire communities.

Ground shaking: Ground shaking is both a hazard created by earthquakes and the trigger for other hazards such as liquefaction and landslides. Ground shaking describes the vibration of the ground during an earthquake. Most earthquake damage results from the shaking caused by seismic waves passing beneath buildings, roads, and other structures. For example, ground shaking may cause a store’s exterior building walls to crumble, injuring people, blocking sidewalks and streets and bringing down utility lines.

Landslides: Earthquakes can trigger landslides, especially in areas with water-saturated soils, a common characteristic of Cascadia. Landslides may result in falling rocks and debris that collide with people, buildings and vehicles. They also can block roads and disrupt utility lines.

Liquefaction: Liquefaction describes the way in which soil liquefies during ground shaking. Liquefaction can undermine the foundations and supports of buildings, bridges, pipelines, and roads, causing them to sink into the ground, collapse or dissolve. Learn more about liquifacation.

Tsunami: Inland earthquakes, such as the 2001 Nisqually earthquake, will not result in tsunamis because they do not uplift the seafloor. However, an offshore subduction zone earthquake or an earthquake generated somewhere else around the Pacific Ocean will generate a tsunami, which is actually a series of waves. In some cases, waves may be up to 33 feet (10 meters) high, flooding everything in their path. Tsunamis can injure or kill many people and cause significant damage to buildings and other structures. People can escape tsunamis by moving to higher ground or far inland after ground shaking stops.

For more information, please see What are my hazards?