Solving the Mystery of the Magnitude 9 Earthquake

NEHRP Success Story

Nisqually Earthquake, February 28, 2001"The City of Seattle did not suffer major damage from the Nisqually earthquake two years ago based, in large part, on our ability to aggressively explain our continuing advances in understanding earthquake hazards to the structural engineering and community emergency response community to ensure that USGS results are used."
-Craig Weaver, Pacific Northwest Regional Coordinator, United States Geological Survey

Lewis and Clark didn't reach the coast of Washington State until November 1805. So how do we know that a magnitude 9 earthquake occurred in the Seattle area on January 26, 1700? Amazingly, the remains of dead, saltwater-flooded forests along coastal Washington and widespread deposits of sand high in coastal estuaries suggesting tsunami inundation, along with an analysis of records maintained by the Japanese on tsunamis, presented evidence to geologists that great subduction-zone earthquakes (magnitude 8 to 9) had repeatedly struck the Pacific Northwest in the past thousand years, the most recent earthquake occurring in 1700. Hard detective work by USGS scientists on the Cascadia subduction zone and other previously unstudied crustal faults has helped residents of western Oregon and Washington understand that they live in earthquake country. Particularly in Oregon, where few earthquakes are felt, USGS research helped convince public officials to significantly revise the building codes. Throughout the heavily urbanized Portland metropolitan region, new buildings are now designed to resist earthquake forces 50 percent larger than they were under the old code, reducing the risk to life and property in future earthquakes.

The impact of earthquake awareness can been seen in Seattle in the effects of the Nisqually earthquake. Although the ground motions were not strong enough to test new design criteria and seismic retrofits, the growing earthquake awareness helped significantly reduce non-structural losses. For example, at The Little Church on The Prairie Learning Center, this awareness played an important part in keeping people safe. Some months before the earthquake, volunteers worked with FEMA hazard mitigation officials to make sure the daycare center would be safe from shaking effects of an earthquake. Mitigation measures included bolting cribs to the walls and strapping water heaters, television sets, and computers in place. When the Nisqually earthquake struck, the children and staff at the Center were protected from falling objects. According to Pat Ivy, Director of the Center, “nothing fell over because of our preventative measures. It was amazing.“

Last Modified: Friday, 19-Oct-2007 11:51:59 EDT