| Abstract: | Fault-zone guided waves were successfully excited by near-surface explosions in the San Andreas fault zone both at Parkfield and Cienega Valley, central California. The guided waves were observed on linear, three-component seismic arrays deployed across the fault trace. These waves were not excited by explosions located outside the fault zone. The amplitude spectra of guided waves show a maximum peak at 2 Hz at Parkfield and 3 Hz at Cienega Valley. The guided wave amplitude decays sharply with observation distance from the fault trace. The explosion-excited fault-zone guided waves are similar to those generated by earthquakes at Parkfield but have lower frequencies and travel more slowly. These observations suggest that the fault-zone wave guide has lower seismic velocities as it approaches the surface at Parkfield. We have modeled the waveforms as S waves trapped in a low-velocity wave guide sandwiched between high-velocity wall rocks, resulting in Love-type fault-zone guided waves. While the results are nonunique, the Parkfield data are adequately fit by a shallow wave guide 170 m wide with an S velocity 0.85 km/sec and an apparent Q ??? 30 to 40. At Cienega Valley, the fault-zone wave guide appears to be about 120 m wide with an S velocity 0.7 km/sec and a Q ??? 30. |
| Genre: | Article |
| ProdID: | 70020131 |
| Citation Author: | Li, Y. -G.; Ellsworth, W. L.; Thurber, C. H.; Malin, P. E.; Aki, K. |
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| Citation End Page: | 221 |
| Citation Issue: | 1 |
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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: | 12 |
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| Citation Search Results Text: | Fault-zone guided waves from explosions in the San Andreas fault at Parkfield and Cienega Valley, California; 1997; Article; Journal; Bulletin of the Seismological Society of America; Li, Y. -G.; Ellsworth, W. L.; Thurber, C. H.; Malin, P. E.; Aki, K. |
| Citation Start Page: | 210 |
| Citation Volume: | 87 |
| Citation Year: | 1997 |
| Type: | citation/reference |
| Text: | Fault-zone guided waves from explosions in the San Andreas fault at Parkfield and Cienega Valley, California; 1997; Article; Journal; Bulletin of the Seismological Society of America; Li, Y. -G.; Ellsworth, W. L.; Thurber, C. H.; Malin, P. E.; Aki, K. |
| URL (THUMBNAIL): | http://pubs.er.usgs.gov/thumbnails/outside_thumb.jpg |
| Date Other: | Wed, 1 Jan 1997 00:00 -0600 |
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