Walck, Marianne C. and Clayton, Robert W.
P wave velocity variations in the Coso Region, California, derived from local earthquake travel times.
Journal of Geophysical Research B, 92
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Inversion of 4036 P wave travel time residuals from 429 local earthquakes using a tomographic scheme provides information about three-dimensional upper crustal velocity variations in the Indian Wells Valley-Coso region of southeastern California. The residuals are calculated relative to a Coso-specific velocity model, corrected for station elevation, weighted, and back-projected along their ray paths through models defined with layers of blocks. Slowness variations in the surface layer reflect local geology, including slow velocities for the sedimentary basins of Indian Wells and Rose valleys and relatively fast velocities for the Sierra Nevada and Argus Mountains. In the depth range of 3–5 km the inversion images an area of reduced compressional velocity in western and northern Indian Wells Valley but finds no major velocity variations beneath the Coso volcanic field to the north. These results are consistent with a recent study of anomalous shear wave attenuation in the Coso region. Between 5 and 10 km depth, low-velocity areas (7% slow) appear at the southern end of the Coso volcanics, reaching east to the Coso Basin. Numerical tests of the inversion's resolution and sensitivity to noise indicate that these major anomalies are significant and well-resolved, while other apparent velocity variations in poorly sampled areas are probably artifacts. The seismic data alone are not sufficient to uniquely characterize the physical state of these low-velocity regions. Because of the Coso region's history of Pleistocene bimodal volcanism, high heat flow, geothermal activity, geodetic deformation, and seismic activity, one possibility is to link the zones of decreased P velocity to contemporary magmatic activity.
|Additional Information:||© 1987 by the American Geophysical Union. Received 30 December 1985; revised September 17, 1986; accepted 7 October 1986. This study was supported by the U.S. Department of Energy under contract DE-AC04-76DP00789 and by the U.S. Geological Survey under contract 14-08-0001-G1171. Some of the
graphics and computational facilities were provided by the W. M. Keck Foundation. We thank Chris Sanders and Hiroo Kanamori for their close cooperation during this study and their critical reviews of the manuscript. The assistance of Carl Johnson and Doug Given of the USGS Pasadena office was invaluable in obtaining the earthquake data. Greg Elbring provided computer graphics expertise. Contribution 4251, Division of Geological and Planetary Sciences, California
Institute of Technology, Pasadena, California.
|Funding Agency||Grant Number|
|Department of Energy (DOE)||DE-AC04-76DP00789|
|Subject Keywords:||Seismology: Body waves; Seismology: Seismicity; Seismology: Structure of the crust; Tectonophysics: Physics of magma and magma bodies
|Other Numbering System:|
|Other Numbering System Name||Other Numbering System ID|
|Caltech Division of Geological and Planetary Sciences||4251|
|Official Citation:||Walck, M. C. and R. W. Clayton (1987), P wave velocity variations in the Coso Region, California, derived from local earthquake travel times, J. Geophys. Res., 92(B1), 393–405, doi:10.1029/JB092iB01p00393|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited On:||03 Oct 2012 15:52|
|Last Modified:||31 Jan 2017 21:42|
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