Toward resolving an earthquake ground motion mystery in west Seattle, Washington State: Shallow seismic focusing may cause anomalous chimney damage
Geophysical Research Letters
By: W. J. Stephenson, A.D. Frankel, J. K. Odum, R. A. Williams, and T. L. Pratt
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Abstract
A shallow bedrock fold imaged by a 1.3-km long high-resolution shear-wave seismic reflection profile in west Seattle focuses seismic waves arriving from the south. This focusing may cause a pocket of amplified ground shaking and the anomalous chimney damage observed in earthquakes of 1949, 1965 and 2001. The 200-m bedrock fold at ???300-m depth is caused by deformation across an inferred fault within the Seattle fault zone. Ground motion simulations, using the imaged geologic structure and northward-propagating north-dipping plane wave sources, predict a peak horizontal acceleration pattern that matches that observed in strong motion records of the 2001 Nisqually event. Additionally, a pocket of chimney damage reported for both the 1965 and the 2001 earthquakes generally coincides with a zone of simulated amplification caused by focusing. This study further demonstrates the significant impact shallow (<1km) crustal structures can have on earthquake ground-motion variability.
Suggested Citation
Stephenson, W.J., Frankel, A., Odum, J.K., Williams, R.A., Pratt, T.L., 2006, Toward resolving an earthquake ground motion mystery in west Seattle, Washington State: Shallow seismic focusing may cause anomalous chimney damage: Geophysical Research Letters, v. 33, no. 6, https://doi.org/10.1029/2005GL025037.
| Publication type | Article |
|---|---|
| Publication Subtype | Journal Article |
| Title | Toward resolving an earthquake ground motion mystery in west Seattle, Washington State: Shallow seismic focusing may cause anomalous chimney damage |
| Series title | Geophysical Research Letters |
| DOI | 10.1029/2005GL025037 |
| Volume | 33 |
| Issue | 6 |
| Publication Date | March 30, 2006 |
| Year Published | 2006 |
| Language | English |
| Larger Work Type | Article |
| Larger Work Subtype | Journal Article |
| Larger Work Title | Geophysical Research Letters |