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Abstract
Waveform and spectral characteristics of several aftershocks of the M 6.1 22 April 1992 Joshua Tree earthquake recorded at stations just north of the Indio Hills in the Coachella Valley can be interpreted in terms of waves propagating within narrow, low-velocity, high-attenuation, vertical zones. Evidence for our interpretation consists of: (1) emergent P arrivals prior to and opposite in polarity to the impulsive direct phase; these arrivals can be modeled as headwaves indicative of a transfault velocity contrast; (2) spectral peaks in the S wave train that can be interpreted as internally reflected, low-velocity fault-zone wave energy; and (3) spatial selectivity of event-station pairs at which these data are observed, suggesting a long, narrow geologic structure. The observed waveforms are modeled using the analytical solution of Ben-Zion and Aki (1990) for a plane-parallel layered fault-zone structure. Synthetic waveform fits to the observed data indicate the presence of NS-trending vertical fault-zone layers characterized by a thickness of 50 to 100 m, a velocity decrease of 10 to 15% relative to the surrounding rock, and a P-wave quality factor in the range 25 to 50.
| Publication type | Article |
|---|---|
| Publication Subtype | Journal Article |
| Title | Fault-zone waves observed at the southern Joshua Tree earthquake rupture zone |
| Series title | Bulletin of the Seismological Society of America |
| Volume | 84 |
| Issue | 3 |
| Year Published | 1994 |
| Language | English |
| Publisher | Seismological Society of America |
| Description | 7 p. |
| First page | 761 |
| Last page | 767 |
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