| Abstract: | Simple spectral ratio (SSR) and horizontal-to-vertical (HN) site-response estimates at 47 sites in the Puget Lowland of Washington State document significant attenuation of 1.5- to 20-Hz shear waves within sedimentary basins there. Amplitudes of the horizontal components of shear-wave arrivals from three local earthquakes were used to compute SSRs with respect to the average of two bedrock sites and H/V spectral ratios with respect to the vertical component of the shear-wave arrivals at each site. SSR site-response curves at thick basin sites show peak amplifications of 2 to 6 at frequencies of 3 to 6 Hz, and decreasing spectra amplification with increasing frequency above 6 Hz. SSRs at nonbasin sites show a variety of shapes and larger resonance peaks. We attribute the spectral decay at frequencies above the amplification peak at basin sites to attenuation within the basin strata. Computing the frequency-independent, depth-dependent attenuation factor (Qs,int) from the SSR spectral decay between 2 and 20 Hz gives values of 5 to 40 for shallow sedimentary deposits and about 250 for the deepest sedimentary strata (7 km depth). H/V site responses show less spectral decay than the SSR responses but contain many of the same resonance peaks. We hypothesize that the H/V method yields a flatter response across the frequency spectrum than SSRs because the H/V reference signal (vertical component of the shear-wave arrivals) has undergone a degree of attenuation similar to the horizontal component recordings. Correcting the SSR site responses for attenuation within the basins by removing the spectral decay improves agreement between SSR and H/V estimates. |
| Genre: | Article |
| ProdID: | 70031198 |
| Citation Author: | Pratt, T. L.; Brocher, T. M. |
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| Citation End Page: | 552 |
| 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: | 17 |
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| Citation Search Results Text: | Site response and attenuation in the Puget Lowland, Washington State; 2006; Article; Journal; Bulletin of the Seismological Society of America; Pratt, T. L.; Brocher, T. M. |
| Citation Start Page: | 536 |
| Citation Volume: | 96 |
| Citation Year: | 2006 |
| Type: | citation/reference |
| Text: | Site response and attenuation in the Puget Lowland, Washington State; 2006; Article; Journal; Bulletin of the Seismological Society of America; Pratt, T. L.; Brocher, T. M. |
| URL (THUMBNAIL): | http://pubs.er.usgs.gov/thumbnails/outside_thumb.jpg |
| URL (DIGITAL OBJECT IDENTIFIER): | http://dx.doi.org/10.1785/0120040200 |
| Date Other: | Sun, 1 Jan 2006 00:00 -0600 |
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