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USGS · 70020131

Fault-zone guided waves from explosions in the San Andreas fault at Parkfield and Cienega Valley, California

Y.-G. Li·W.L. Ellsworth·C.H. Thurber·P.E. Malin·K. Aki
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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.

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Bulletin of the Seismological Society of AmericaArticle
90° N90° S · 180° W ← longitude → 180° E
Source-reported bounding extent: 35.40874868089202° to 37.09198944946155° latitude; -121.66901999753915° to -119.80683738035154° longitude. This indicates report coverage, not an exact sampling location. View area on OpenStreetMap.

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BibTeXRIS

Y.-G. Li, W.L. Ellsworth, C.H. Thurber, P.E. Malin, K. Aki. 1997-02-01. Fault-zone guided waves from explosions in the San Andreas fault at Parkfield and Cienega Valley, California. https://doi.org/10.1785/bssa0870010210

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