Fault-zone guided waves from explosions in the San Andreas fault at Parkfield and Cienega Valley, California
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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.
Study Area
| Publication type | Article |
|---|---|
| Publication Subtype | Journal Article |
| Title | Fault-zone guided waves from explosions in the San Andreas fault at Parkfield and Cienega Valley, California |
| Series title | Bulletin of the Seismological Society of America |
| DOI | 10.1785/BSSA0870010210 |
| Volume | 87 |
| Issue | 1 |
| Year Published | 1997 |
| Language | English |
| Publisher | Seismological Society of America |
| Description | 12 p. |
| First page | 210 |
| Last page | 221 |
| Country | United States |
| State | California |
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