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Anomalous shear wave attenuation in the shallow crust beneath the Coso Volcanic Region, California

Sanders, Chris and Ho-Liu, Phyllis and Rinn, David and Kanamori, Hiroo (1988) Anomalous shear wave attenuation in the shallow crust beneath the Coso Volcanic Region, California. Journal of Geophysical Research B, 93 (B4). pp. 3321-3338. ISSN 0148-0227. doi:10.1029/JB093iB04p03321.

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We use seismograms of local earthquakes to image relative shear wave attenuation structure in the shallow crust beneath the region containing the Coso volcanic-geothermal area of eastern California. SV and P wave amplitudes were measured from vertical component seismograms of earthquakes that occurred in the Cososouthem Sierra Nevada region from July 1983 to August 1985. Seismograms of 16 small earthquakes show SV amplitudes which are greatly diminished at some azimuths and takeoff angles, indicating strong lateral variations in S wave attenuation in the area. Three-dimensional images of the relative S wave attenuation structure are obtained from forward modeling and a back projection inversion of the amplitude data. The results indicate regions within a 20 by 30 by 10 km volume of the shallow crust (one shallower than 5 km) that severely attenuate SV waves passing through them. These anomalies lie beneath the Indian Wells Valley, 30 km south of the Coso volcanic field, and are coincident with the epicentral locations of recent earthquake swarms. No anomalous attenuation is seen beneath the Coso volcanic field above about 5 km depth. Geologic relations and the coincidence of anomalously slow P wave velocities suggest that the attenuation anomalies may be related to magmatism along the eastern Sierra front.

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Kanamori, Hiroo0000-0001-8219-9428
Additional Information:© 1988 by the American Geophysical Union. Paper number 6B6200. Received July 16, 1986; revised September 4, 1987; accepted October 4, 1987. Glenn Roquemore and John Zellmer of the Naval Weapons Center, China Lake, California provided informative discussions about and field trips into the Indian Wells Valley-Coso region. Susan Boundy provided a review and helped draft figures, Lucy Jones assisted with some data acquisition, and Christof Stork wrote the ray-tracing program used in the inversion. Marianne Walck and Robert Clayton discussed their P wave travel time results with us. Roy Bailey provided helpful discussions and a review. This work was supported by U.S. Geological Survey contract 14-08-001-21981 and grant 14-08-001-G1170. This is contribution 4355 of the Division of Geological and Planetary Sciences, California Institute of Technology.
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Caltech Division of Geological and Planetary Sciences4355
Issue or Number:B4
Record Number:CaltechAUTHORS:20141104-155108790
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Official Citation:Sanders, C., P. Ho-Liu, D. Rinn, and H. Kanamori (1988), Anomalous shear wave attenuation in the shallow crust beneath the Coso Volcanic Region, California, J. Geophys. Res., 93(B4), 3321–3338, doi:10.1029/JB093iB04p03321
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:51260
Deposited By: Tony Diaz
Deposited On:05 Nov 2014 00:03
Last Modified:10 Nov 2021 19:08

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