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Surface seismic measurements of near-surface P-and S-wave seismic velocities at earthquake recording stations, Seattle, Washington

R. A. Williams·W. J. Stephenson·A.D. Frankel·J. K. Odum
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Abstract

We measured P - and S -wave seismic velocities to about 40-m depth using seismic-refraction/reflection data on the ground surface at 13 sites in the Seattle, Washington, urban area, where portable digital seismographs recently recorded earthquakes. Sites with the lowest measured V s correlate with highest ground motion amplification. These sites, such as at Harbor Island and in the Duwamish River industrial area (DRIA) south of the Kingdome, have an average V s in the upper 30 m (V¯ s30 ) of 150 to 170 m/s. These values of V¯ s30 place these sites in soil profile type E (V¯ s30 < 180 m/s). A “rock” site, located at Seward Park on Tertiary sedimentary deposits, has a V¯ s30 of 433 m/s, which is soil type C (V¯ s30 : 360 to 760 m/s). The Seward Park site V¯ s30 is about equal to, or up to 200 m/s slower than sites that were located on till or glacial outwash. High-amplitude P - and S -wave seismic reflections at several locations appear to correspond to strong resonances observed in earthquake spectra. An S -wave reflector at the Kingdome at about 17 to 22 m depth probably causes strong 2-Hz resonance that is observed in the earthquake data near the Kingdome.

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Earthquake SpectraArticle
90° N90° S · 180° W ← longitude → 180° E
Source-reported bounding extent: 47.42606865799539° to 47.85061625161839° latitude; -122.46630692838912° to -122.11212927636791° longitude. This indicates report coverage, not an exact sampling location. View area on OpenStreetMap.

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R. A. Williams, W. J. Stephenson, A.D. Frankel, J. K. Odum. 1999-08-01. Surface seismic measurements of near-surface P-and S-wave seismic velocities at earthquake recording stations, Seattle, Washington. https://doi.org/10.1193/1.1586059

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