| Abstract: | Recordings of the 1999 Mw 7.6 Chi-Chi (Taiwan) earthquake, two local earthquakes, and five blasts show seismic-wave amplification over a large sedimentary basin in the U.S. Pacific Northwest. For weak ground motions from the Chi-Chi earthquake, the Seattle basin amplified 0.2- to 0.8-Hz waves by factors of 8 to 16 relative to bedrock sites west of the basin. The amplification and peak frequency change during the Chi-Chi coda: the initial S-wave arrivals (0-30 sec) had maximum amplifications of 12 at 0.5-0.8 Hz, whereas later arrivals (35-65 sec) reached amplifications of 16 at 0.3-0.5 Hz. Analysis of local events in the 1.0- to 10.0-Hz frequency range show fourfold amplifications for 1.0-Hz weak ground motion over the Seattle basin. Amplifications decrease as frequencies increase above 1.0 Hz, with frequencies above 7 Hz showing lower amplitudes over the basin than at bedrock sites. Modeling shows that resonance in low-impedance deposits forming the upper 550 m of the basin beneath our profile could cause most of the observed amplification, and the larger amplification at later arrival times suggests surface waves also play a substantial role. These results emphasize the importance of shallow deposits in determining ground motions over large basins. |
| Genre: | Article |
| ProdID: | 70025760 |
| Citation Author: | Pratt, T. L.; Brocher, T. M.; Weaver, C. S.; Creager, K. C.; Snelson, C. M.; Crosson, R. S.; Miller, K. C.; Trehu, A. M. |
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| Citation End Page: | 545 |
| Citation Issue: | 2 |
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| Citation Language: | English |
| Citation Larger Work Title: | Bulletin of the Seismological Society of America |
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| Citation Number Of Pages: | 13 |
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| Citation Search Results Text: | Amplification of seismic waves by the Seattle basin, Washington State; 2003; Article; Journal; Bulletin of the Seismological Society of America; Pratt, T. L.; Brocher, T. M.; Weaver, C. S.; Creager, K. C.; Snelson, C. M.; Crosson, R. S.; Miller, K. C.; Trehu, A. M. |
| Citation Start Page: | 533 |
| Citation Volume: | 93 |
| Citation Year: | 2003 |
| Type: | citation/reference |
| Text: | Amplification of seismic waves by the Seattle basin, Washington State; 2003; Article; Journal; Bulletin of the Seismological Society of America; Pratt, T. L.; Brocher, T. M.; Weaver, C. S.; Creager, K. C.; Snelson, C. M.; Crosson, R. S.; Miller, K. C.; Trehu, A. M. |
| URL (THUMBNAIL): | http://pubs.er.usgs.gov/thumbnails/outside_thumb.jpg |
| Date Other: | Wed, 1 Jan 2003 00:00 -0600 |
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