Live in the Seattle area long enough and you’ll experience an earthquake. Most earthquakes in the Northwest are minor. Some you may not even feel. Others, like the 2001 Nisqually Earthquake, are large enough to feel and cause some damage. But make no mistake—the Seattle-Tacoma area has the potential to have large and destructive quakes! The Puget Sound Region is crisscrossed by fault lines and zones and also located close to the Cascadia Subduction Zone, where the Juan de Fuca and North American tectonic plates meet. According to the Washington state Department of Natural Resources, more than 1,000 earthquakes happen in Washington state each year! Living in such a seismically active area, it’s not a matter of if we have a major earthquake, but when.
Also see: Natural Disasters in the Seattle Area
Types of Earthquakes in the Puget Sound
Depending on how deep an earthquake is and the type of fault it takes place on, earthquakes can be minor or major, close to the surface or deep within the earth. The Puget Sound has the potential to experience three different types of earthquakes: shallow, deep and subduction. Shallow and deep quakes are just what they sound like—shallow earthquakes take place between 0 and 30 km from the surface; deep earthquakes take place between 35 and 70 km from the surface.
Subduction earthquakes in our region take place along the Cascadia Subduction Zone off of the Washington Coast. Subduction is when one plate moves underneath another plate and these are the quakes largely responsible for tsunamis and high magnitudes. Subduction zones (including Cascadia) are capable of producing what are called megathrust earthquakes, which are massively powerful and destructive, if they take place in a populated area. The 2011 Tohoku earthquake in Japan took place along a subduction zone similar to the Cascadia Subduction Zone.
The Puget Sound area is frequently subject to small earthquakes that most people don’t even feel and that don’t cause any damage. Over the past several hundred years, a few earthquakes have made history for their higher magnitudes and damages left in their wakes.
February 28, 2001: The Nisqually Earthquake, at 6.8 magnitude, was centered to the south in Nisqually, but caused some structural damage all the way in Seattle.
April 29, 1965: A 6.5 magnitude, deep earthquake in the south Sound area was felt as far away as Montana and British Columbia, and knocked down thousands of chimneys in the Puget Sound.
April 13, 1949: A 7.0 quake was centered near Olympia and caused eight deaths, vast property damage in Olympia, and a huge mudslide in Tacoma.
February 14, 1946: A magnitude 6.3, deep quake earthquake rocked most of the Puget Sound and caused major damage in Seattle.
June 23, 1946: A 7.3 magnitude quake was centered in the Strait of Georgia and caused some damage in Seattle. The earthquake was felt from Bellingham to Olympia.
1872: Centered near Lake Chelan, this earthquake is estimated to have been large, but there were few manmade structures in its path. Most reports center on landslides and ground fissures.
January 26, 1700: The last-known megathrust earthquake near Seattle was in 1700. Evidence of a massive tsunami (that may even have struck Japan) and destruction of forests helps scientists date this quake.
Around 900 AD: It’s estimated that a 7.4 magnitude quake hit the Seattle area in about 900. Local legends and geology help confirm this earthquake.