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A study of possible ground-motion amplification at the Coyote Lake Dam, California

Bulletin of the Seismological Society of America

By:
, , , and
DOI: 10.1785/012003144

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Abstract

The abutment site at the Coyote Lake Dam recorded an unusually large peak acceleration of 1.29g during the 1984 Morgan Hill earthquake. Following this earthquake another strong-motion station was installed about 700 m downstream from the abutment station. We study all events (seven) recorded on these stations, using ratios of peak accelerations, spectral ratios, and particle motion polarization (using holograms) to investigate the relative ground motion at the two sites. We find that in all but one case the motion at the abutment site is larger than the downstream site over a broad frequency band. The polarizations are similar for the two sites for a given event, but can vary from one event to another. This suggests that the dam itself is not strongly influencing the records. Although we can be sure that the relative motion is usually larger at the abutment site, we cannot conclude that there is anomalous site amplification at the abutment site. The downstream site could have lower-than-usual near-surface amplifications. On the other hand, the geology near the abutment site is extremely complex and includes fault slivers, with rapid lateral changes in materials and presumably seismic velocities. For this reason alone, the abutment site should not be considered a normal free-field site.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
A study of possible ground-motion amplification at the Coyote Lake Dam, California
Series title:
Bulletin of the Seismological Society of America
DOI:
10.1785/012003144
Volume
94
Issue:
4
Year Published:
2004
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Bulletin of the Seismological Society of America
First page:
1327
Last page:
1342
Number of Pages:
16