Observations of earthquake source parameters at 2 km depth in the Long Valley Caldera, eastern California
Bulletin of the Seismological Society of America
By: Stephanie G. Prejean and William L. Ellsworth
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Abstract
To investigate seismic source parameter scaling and seismic efficiency in the Long Valley caldera, California, we measured source parameters for 41 earthquakes (M 0.5 to M 5) recorded at 2 km depth in the Long Valley Exploratory Well. Borehole recordings provide a wide frequency bandwidth, typically 1 to 200–300 Hz, and greatly reduce seismic noise and path effects compared to surface recordings. We calculated source parameters in both the time and frequency domains for P and S waves. At frequencies above the corner frequency, spectra decay faster than ω3, indicating that attenuation plays an important role in shaping the spectra (path averaged Qp = 100–400, Qs = 200–800). Source parameters are corrected for attenuation and radiation pattern.
Both static stress drops and apparent stresses range from approximately 0.01 to 30 MPa. Although static stress drops do not vary with seismic moment for these data, our analyses are consistent with apparent stress increasing with increasing moment. To estimate tectonic driving stress and seismic efficiencies in the region, we combined source parameter measurements with knowledge of the stress field and a Coulomb failure criterion to infer a driving stress of 40–70 MPa. Subsequent seismic efficiencies are consistent with McGarr's (1999) hypothesis of a maximum seismic efficiency of 6%.
Suggested Citation
Prejean, S.G., and Ellsworth, W.L., 2001, Observations of earthquake source parameters at 2 km depth in the Long Valley Caldera, eastern California: Bulletin of the Seismological Society of America, v. 91, no. 2, p. 165-177, https://doi.org/10.1785/0120000079.
ISSN: 1943-3573 (online)
Study Area
| Publication type | Article |
|---|---|
| Publication Subtype | Journal Article |
| Title | Observations of earthquake source parameters at 2 km depth in the Long Valley Caldera, eastern California |
| Series title | Bulletin of the Seismological Society of America |
| DOI | 10.1785/0120000079 |
| Volume | 91 |
| Issue | 2 |
| Year Published | 2001 |
| Language | English |
| Publisher | Seismological Society of America |
| Contributing office(s) | Alaska Science Center |
| Description | 13 p. |
| Larger Work Type | Article |
| Larger Work Subtype | Journal Article |
| Larger Work Title | Bulletin of the Seismological Society of America |
| First page | 165 |
| Last page | 177 |
| Country | United States |
| State | California |
| Other Geospatial | Long Valley Caldera |