Where were you at 10:54 AM on February 28th, 2001? At that moment 20 years ago, there was a whole lotta shaking going on as the Nisqually Earthquake struck Western Washington. The 6.8 magnitude quake was centered about 35 miles deep near Anderson Island in South Puget Sound and shook for just under a minute. The earthquake caused about $1 to 2 billion in damage, one person died from a heart attack, and about 400 were injured.
The most serious damage occurred near the epicenter or involved older unreinforced masonry or concrete buildings. Damages included parts of older downtown Seattle, the capitol building in Olympia, the Boeing Field runway, and the air traffic control tower at SeaTac Airport.
Damage in the North Sound was quite limited. Yet, many of those in schools and businesses got to practice their drop, cover and hold skills for real.
Elsewhere, the SR 99 Alaskan Way Viaduct in Seattle remained standing but suffered some support sagging and was deemed to fail in another earthquake. The Viaduct was recently replaced with a new tunnel that is designed to withstand a 9.0 magnitude earthquake. The Seattle waterfront seawall also suffered damage and is in the process of being fully replaced.
Western Washington is prone to earthquakes, ranking number two in the lower 48 states behind California. The primary cause of these earthquakes is the subduction of the offshore Juan de Fuca tectonic plate under the North American plate. The Juan de Fuca plate is sliding under the North American plate at about 3.5 to 4.5 centimeters per year, placing Western Washington under growing pressure.
About 100 miles off the Pacific Northwest coast is the Cascadia Subduction Zone where the Juan de Fuca plate is sliding under the North American plate. Thisplate movement is also what generated the Cascade volcanoes and keeps them active in geologic time. The Cascadia Subduction Zone is part of the Pacific Ocean Ring of Fire where the majority of the globe’s biggest earthquakes and volcanic eruptions have occurred.
The subduction zone produces three types of earthquakes in our region. The big ones are rare megathrust events such as the Cascadia earthquake, the last to occur on January 26th, 1700, and occur about every 300 to 500 years. The other types include shallow North American plate events and deep intra-slab events within the subsiding Juan de Fuca plate. This last type involved the Nisqually quake as well as the April 29, 1965, and April 13, 1949 (both magnitude 6.7) earthquakes in Western Washington.
Earthquakes are no-notice events. Yet in the near future, an early earthquake warning system will come online. Testing of this system is underway and in May, the new “ShakeAlert” Earthquake Early Warning System will make its debut. This system will send alerts to wireless devices, giving residents critical seconds of lead time to prepare and take action before the shaking gets started. Created by the U.S. Geological Survey (USGS), this system uses a network of earthquake sensors throughout the west coast that can detect a quake and provide information such as the location, magnitude and expected duration via your wireless device as well as many media mediums like TV, radio and internet.
You can get ready for earthquakes in advance. Remember to drop, cover and hold on when an earthquake starts. You can practice this safety technique with your family. In addition, make an emergency plan and protect your home. Also include a communication plan in case the quake strikes when your family is separated at work, school or on the road.
Visit ready.gov for all your earthquake preparedness guidelines, including what to do if the earthquake strikes while you are sleeping in bed, driving a car, or you are outdoors.
The 20th anniversary of the Nisqually earthquake gives all of us a reminder that the North Sound is earthquake country and that we need to prepare in advance so we are ready when a quake hits.