2001 Nisqually Earthquake

At 10:54 a.m. local time on February 28th, 2001, the regular hustle and bustle of the Puget Sound area came to an abrupt halt as a magnitude (Mw) 6.8 earthquake shook the region. The hypocenter was located beneath Anderson Island, some 17 kilometers from Olympia, Washington, near the Nisqually River Delta. The earthquake happened on a normal fault 52 kilometers deep within the subducting Juan de Fuca plate. The fault rupture sent seismic waves that were felt throughout the Puget Sound Region and into Oregon, Idaho, and British Columbia.

The shaking caused significant property damage in Western Washington. The Nisqually earthquake is estimated to have caused approximately $305 million in insured losses and $2 billion in total damage. Important structures such as the Alaskan Way Viaduct and the Washington State Capitol Building, as well as buildings in Seattle’s Pioneer Square neighborhood, were damaged by the event. Four hundred people were injured, and one death was attributed to the earthquake. A number of landslides occurred, some causing damage to roads and homes.

The Nisqually earthquake was a deep intraplate earthquake (Deep Earthquakes). In the Pacific Northwest, these types of earthquakes occur within the subducting Juan de Fuca plate along the Cascadia Subduction Zone, 30 to 70 kilometers beneath the surface; Nisqually’s hypocenter was about 52 kilometers underground. As the Juan de Fuca plate descends beneath the North American plate, it bends and encounters increasing temperature and pressure. Stress from this process results in the rupture of normal faults, creating deep intraplate earthquakes. Due to their depth, the energy released during these events is able to spread out before it reaches the surface. This results in less severe shaking directly at the epicenter, but the higher levels of shaking are felt over a larger area. Typically, these types of earthquakes in the Puget Sound produce very few aftershocks. There were two aftershocks attributed to the Nisqually earthquake: a Mw 3.4 event about 6 kilometers north of the mainshock and a Mw 2.7 event about 2.5 kilometers north of the mainshock, both on March 1st.

Though other types of earthquakes, like those on crustal faults or the Cascadia Subduction Megathrust fault, can be more damaging due to their proximity to cities and their size, respectively, deep earthquakes occur much more frequently in the Puget Sound Region. Deep intraplate earthquakes have been responsible for most of the notable seismic events in recent Pacific Northwest history. The 1909 Mw 6.0, 1939 Mw 6.2, 1949 Mw 7.1, and 1965 Mw 6.7 earthquakes were all deep intraplate quakes. This type of earthquake occurs on average every 30 years and there is an estimated 84% chance of another one with a magnitude larger than 6.0 happening in the next 50 years.

The worst of the property damage was contained within the Puget Lowlands, but the earthquake’s effects varied dramatically even between neighboring cities. The worst-hit areas were Olympia, Sea-Tac Airport, and Seattle’s Pioneer Square. But Tacoma, for example, did not experience as much damage despite being located between Olympia and Seattle and relatively near the epicenter. This is due to variations in the soil, sediment, and bedrock that lie under Western Washington. Seismic waves travel differently through different materials (Site Effects), so the ground motion experienced in one area could be very different from that in another location nearby. Landslides, liquefaction, and lateral spreading all occurred as a result of the earthquake (Earthquake Hazards.

Buildings throughout the Puget Sound Region faced structural and non-structural damage. The worst of the structural damage occurred primarily in unreinforced masonry buildings (URMs) such as the brick buildings in Pioneer Square. Over a thousand URMs were red-tagged or yellow-tagged — meaning that an engineer inspected them and found them unsafe for re-occupancy — as a result of wall collapse, cracking, or falling bricks. Other types of buildings fared better structurally, but non-structural damage was extensive. Damage to windows, ceiling and wall finishes, electrical components, piping, etc., affected buildings of all types. Non-structural damage resulted in service disruptions at large companies such as Starbucks, Boeing, and Amazon, as well as local and state government offices. A number of schools had to temporarily close and SeaTac Airport had to reduce service to about 50% of normal. The Washington State Capitol Building was closed for over three years because the dome shifted as a result of shaking. The Alaskan Way Viaduct in Seattle sustained damage that required immediate repairs and led to its eventual replacement by the SR 99 Tunnel.

The Nisqually earthquake shook the ground for over 30 seconds. In addition to the direct damage to buildings, this shaking also caused many ground failures throughout the region. Researchers observed landslides, settlement and lateral spreading, liquefaction, changes in groundwater flow paths, and flooding as a result of the earthquake. Landslides caused damage to numerous structures and knocked out utilities to many communities. 

Shaking from the Nisqually earthquake also induced liquefaction throughout the region, even as far away as Mt. St. Helens. The shaking of loose sediment resulted in sand boils, sand fountains, cracking, and subsidence. The runway at Boeing Field in Seattle experienced many sand and debris ejections resulting in extensive cleanup before operations could be resumed.

Though the damage from the Nisqually earthquake was far-reaching and costly, things could have been much worse. There were relatively few injuries and casualties, and structural damage to buildings and infrastructure was limited. The majority of the economic loss came as a result of non-structural damage and disruption of business rather than loss of lives and structures. Emergency operations and healthcare systems all functioned quickly and efficiently to respond to the event. There is evidence that seismic retrofitting and newer buildings built to higher standards performed better and faced less damage.

The earthquake serves as a reminder that being properly prepared for a damaging earthquake can save lives and reduce damage. Retrofitting older buildings and performing non-structural hazard mitigation can greatly reduce hazards to human life and property during an earthquake. Make sure you know what to do during and after an earthquake – if you feel shaking, Drop, Cover, and Hold On. Have an emergency kit prepared and accessible. Earthquakes like Nisqually don’t have to be devastating; simple preparation steps can greatly reduce injuries, loss of life, and damage.

For additional information about the 2001 Nisqually earthquake:

For more information about how to prepare for an earthquake, visit this page: Preparedness.