Seattle Earthquake Site Response
Immediately following the magnitude 5.3 Duvall earthquake of 3 May 1996, the U. S. Geological Survey installed an array of 15 seismographs in urban Seattle to record ground motion caused by Duvall aftershocks and other earthquakes that occur nearby. We are using the earthquake records to measure how much the ground motion is amplified at sites located on sediments and fill compared to sites located on hard rock. The goal of the site response study is to define the earthquake shaking that can be expected to affect the city on a neighborhood-by-neighborhood basis.
The seismograph array recorded 14 events during 1997, including the magnitude 3.5 Beacon Hill earthquake of 10 February 1997 and the magnitude 4.7 Bremerton earthquake of 23 June 1997.
The Beacon Hill earthquake record section displays the N-S components of ground velocity (high-pass filtered at 2 Hz) produced by that event that were recorded at several sites in Seattle. The earthquake occurred directly under the urban area where it was felt by many people. The records of ground motion from this event show that sites underlain by artificial fill such as Harbor Island, King Dome, and the Warehouse District (Sodo) experience several times more shaking than sites in Seattle built on the glacial moraine hills or the rock site at Seward Park.
The Bremerton earthquake record section displays the three-component ground accelerations recorded at several sites in Seattle produced by that event.
The seismogram of the Bremerton earthquake recorded at Seward Park is shown in detail, and as a data file. The peak ground motion produced at this site by this earthquake is twice the peak motion produced by the Beacon Hill earthquake at the same site.
Detailed analysis of these data is used by city planners to influence development, the insurance industry to estimate potential losses, and engineers to build more earthquake resistant buildings.
