W.L. Ellsworth
C.H. Thurber
P.E. Malin
K. Aki
Y.-G. Li
1997
<div id="136101989" class="article-section-wrapper js-article-section js-content-section " data-section-parent-id="0"><p>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<span> </span><i>S</i><span> </span>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<span> </span><i>S</i><span> </span>velocity 0.85 km/sec and an apparent<span> </span><i>Q</i><span> </span>∼ 30 to 40. At Cienega Valley, the fault-zone wave guide appears to be about 120 m wide with an<span> </span><i>S</i><span> </span>velocity 0.7 km/sec and a<span> </span><i>Q</i><span> </span>∼ 30.</p></div>
application/pdf
10.1785/BSSA0870010210
en
Seismological Society of America
Fault-zone guided waves from explosions in the San Andreas fault at Parkfield and Cienega Valley, California
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