Earthquakes

Header Image
Mercer Slough Oct. 2017.JPG
 

Earthquakes occur around here almost on a daily basis, many of them not having enough impact to even be noticed. When a major tremor does strike, you will want to be prepared and know what to do during and after.

Pictograms

What should you do if a major earthquake strikes? The pictograms on this page, presented in multiple languages, are helpful.

አማርኛ - Amharic 한국어 - Korean
عربى - Arabic ਪੰਜਾਬੀ - Punjabi
繁體中文 - Chinese Русский - Russian
English Español - Spanish
فارسی - Farsi اردو - Urdu
हिंदी - Hindi tiếng Việt - Vietnamese
日本語 - Japanese  

 

Background

Washington is situated in a highly active geologic area, which contains shifting tectonic plates, crustal faults and a subduction zone that all produce frequent earthquakes. Three types of earthquakes may occur in our region: megathrust, intraplate (deep) and crustal (shallow).

Crustal faults are caused by the deformation within the North American Plate due to compression by neighboring tectonic plates. Crustal earthquakes occur no deeper than 18 miles below the surface, and can produce earthquakes as large as magnitude 7.5. Several major population hubs are situated directly atop such faults, such as the Seattle Fault which runs directly beneath Seattle and Bellevue. The most recent Seattle Fault earthquake occurred about 1,100 years ago, and has been active three to four times over the past 3,000 years.

The most frequent types of earthquakes in Washington are Interplate (deep). These earthquakes rupture faults within the subducting Juan de Fuca Plate, and are usually less than magnitude 7.5. Because these earthquakes are so deep (18-42 miles beneath the surface), the seismic wave energy spreads over a much larger area than a shallow quake, thus shaking is felt over a larger geographic extent. Historically, interplate earthquakes occur every 10 to 30 years. The USGS estimates that there is an 84% chance of an interplate earthquake of M6.5 or great occurring within the next 50 years. Deep earthquakes larger than M6.0 occurred in 1909, 1939, 1946, 1949, 1965, and most recently on February 28, 2001 with the epicenter under the Nisqually Delta.

Megathrust earthquakes occur at subduction zones, and produce earthquakes as powerful as M9.0. In the Pacific Northwest, megathrust earthquakes occur along the Cascadian Subduction Zone. Historically, these earthquakes reoccur at a 500-year interval.

Seismic Scenario Catalog

The Washington State Seismic Scenario Catalog contains estimates of earthquake damage for a variety of faults in the State of Washington. Explore the catalog to visualize the impacts of different earthquake scenarios.

Recent earthquakes around the world

image of map of recent earthquakes around the world
Earthquakes from the last two weeks provided by the IRIS Seismic Monitor.

Sources

Understanding Earthquake Hazards in Washington State
Deep Earthquakes
 

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