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Observations of earthquake source parameters at 2 km depth in the Long Valley Caldera, eastern California

Bulletin of the Seismological Society of America

By:
and
DOI: 10.1785/0120000079

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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%.

Geospatial Extents

Additional Publication Details

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