Know Your Hazards: Community Threats & How to Prepare for Them
Earthquakes
It’s Not a Matter of If but When.
Earthquakes are part of the past, present, and future of the Pacific Northwest. In the past year*, Washington has experienced over 4,275 earthquakes; most were too small to be felt and have shaken our area for millions of years. The type of earthquakes that are most likely to impact our site are as follows:
*Section was updated on May 23, 2023
Intraplate or Deep Quakes
These earthquakes occur at depths of 30-70 km (about 43.5 mi). Current estimates indicate an 85% chance of a large earthquake around Magnitude 7 occurring on one of these faults within the next 50 years. Deep quakes are the most common large earthquakes known to occur within the Puget Sound region. On February 28, 2001, a 6.8 MMI(severe) earthquake struck from a fault deep under the Nisqually Delta, lasting 45 sections and causing between $1-4 billion in damages.
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- Types of Earthquakes
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- ShakeMap of 2001 Nisqually Earthquake
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- Damage in Port Orchard from Nisqually 2001 earthquake
Subduction Zone or Megathrust Quakes
The Cascadia Subduction Zone (CSZ) is a “megathrust” fault 620 mi long off the west coast, stretching from Northern Vancouver Island to Cape Mendocino, California. It separates the Juan de Fuca and North American plates. The Juan de Fuca plate pushes toward the North American plate at about one inch per year.
There is evidence of 40 significant earthquakes occurring on the CSZ in the last 10,000 years. On the night of January 26, 1700, a magnitude 9.0 earthquake shook the region, sending a tsunami almost immediately inland along the west coast of the US and arriving roughly 10 hours after the quake as a 16-foot wave on the shores of Honshu Island, Japan. The oral history shared by many coastal Tribes in the Northwest tells the story of the Thunderbird and the Whale and the danger of these waves.
Crustal or Shallow Quakes
Resources & More Information
General Awareness Resources:
Earthquake Resources: