Source inversion of the 1988 Upland, California, earthquake: Determination of a fault plane for a small event
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Abstract
We examined short-period P waves to investigate if waveform data could be used to determine which of two nodal planes was the actual fault plane for a small (ML 4.6) earthquake near Upland, California. We removed path and site complications by choosing a small aftershock (ML 2.7) as an empirical Green function. The main shock P waves were deconvolved by using the empirical Green function to produce simple far-field displacement pulses. We used a least-squares method to invert these pulses for the slip distribution on a finite fault. Both nodal planes (strike 125°, dip 85° and strike 221°, dip 40°) of the first-motion focal mechanism were tested at various rupture velocities. The southwest trending fault plane consistently gave better fitting solutions than the southeast-trending plane. We determined a moment of 4.2 × 1022 dyne-cm. The rupture velocity, and thus the source area could not be well resolved, but if we assume a reasonable rupture velocity of 0.87 times the shear wave velocity, we obtain a source area of 0.97 km2 and a stress drop of 38 bars. Choice of a southwest-trending fault plane is consistent with the trend of the nearby portion of the Transverse Ranges frontal fault zone and indicates left-lateral motion. This method provides a way to determine the fault plane for small earthquakes that have no surface rupture and no obvious trend in aftershock locations.
Suggested Citation
Mori, J., and Hartzell, S., 1990, Source inversion of the 1988 Upland, California, earthquake: Determination of a fault plane for a small event: Bulletin of the Seismological Society of America, v. 80, no. 3, p. 507-518, https://doi.org/10.1785/BSSA0800030507.
ISSN: 1943-3573 (online)
Study Area
| Publication type | Article |
|---|---|
| Publication Subtype | Journal Article |
| Title | Source inversion of the 1988 Upland, California, earthquake: Determination of a fault plane for a small event |
| Series title | Bulletin of the Seismological Society of America |
| DOI | 10.1785/BSSA0800030507 |
| Volume | 80 |
| Issue | 3 |
| Publication Date | June 01, 1990 |
| Year Published | 1990 |
| Language | English |
| Publisher | Seismological Society of America |
| Description | 12 p. |
| First page | 507 |
| Last page | 518 |
| Country | United States |
| State | California |