The abrupt release of this slowly accumulated strain causes earthquakes.Įarthquakes at Washington Military Department Emergency Management Division. In addition, the northward-moving Pacific plate is pushing the Juan de Fuca plate north, causing complex seismic strain to accumulate. The two plates are converging at a rate of about 2 inches per year. The Cascadia subduction zone, the fault boundary between the North America plate and the Juan de Fuca plate, lies offshore from northern California to southern British Columbia. The Pacific Northwest is at a convergent continental margin, the collision boundary between two tectonic plates of the earth’s crust. Washington’s earthquake hazards reflect its tectonic setting. Geologic evidence documents prehistoric magnitude 8 to 9.5 earthquakes along the outer coast, and events of magnitude 7 or greater along shallow crustal faults in the urban areas of Puget Sound. While most earthquakes occur in Western Washington, some damaging events, such as the 1872 magnitude 6.8 (est.) quake, do occur east of the Cascades. The earthquake threat in Washington is not uniform. Washington Emergency Management Tsunami Program The first wave can be followed by others a few minutes or a few hours later, and the later waves are commonly larger. In 1946, a tsunami was initiated by an earthquake in the Aleutian Islands of Alaska in less than 5 hours, it reached Hawaii with waves as high as 55 feet and killed 173 people. Offshore tsunamis would strike the adjacent shorelines within minutes and also cross the ocean at speeds as great as 600 miles per hour to strike distant shores.
#Pacific northwest earthquake series
That swift change creates a series of high-energy waves that radiate outward like pond ripples. Tsunamis are generated when these geologic events cause large, rapid movements in the sea floor that displace the water column above. These destructive waves can be caused by coastal or submarine landslides or volcanism, but they are most commonly caused by large submarine earthquakes. The Pacific Coast of Washington is at risk from tsunamis.
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