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Attenuation and Source Properties at the Coso Geothermal Area, California

Hough, S. E. and Lees, J. M. and Monastero, F. (1999) Attenuation and Source Properties at the Coso Geothermal Area, California. Bulletin of the Seismological Society of America, 89 (6). pp. 1606-1619. ISSN 0037-1106.

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We use a multiple-empirical Green's function method to determine source properties of small (M −0.4 to 1.3) earthquakes and P- and S-wave attenuation at the Coso Geothermal Field, California. Source properties of a previously identified set of clustered events from the Coso geothermal region are first analyzed using an empirical Green's function (EGF) method. Stress-drop values of at least 0.5-1 MPa are inferred for all of the events; in many cases, the corner frequency is outside the usable bandwidth, and the stress drop can only be constrained as being higher than 3 MPa. P- and S-wave stress-drop estimates are identical to the resolution limits of the data. These results are indistinguishable from numerous EGF studies of M 2-5 earthquakes, suggesting a similarity in rupture processes that extends to events that are both tiny and induced, providing further support for Byerlee's Law. Whole-path Q estimates for P and S waves are determined using the multiple-empirical Green's function (MEGF) method of Hough (1997), whereby spectra from clusters of colocated events at a given station are inverted for a single attenuation parameter, κ, with source parameters constrained from EGF analysis. The κ estimates, which we infer to be resolved to within 0.01 sec or better, exhibit almost as much scatter as a function of hypocentral distance as do values from previous single-spectrum studies for which much higher uncertainties in individual κ estimates are expected. The variability in κ estimates determined here therefore suggests real lateral variability in Q structure. Although the ray-path coverage is too sparse to yield a complete three-dimensional attenuation tomographic image, we invert the inferred κ value for three-dimensional structure using a damped least-squares method, and the results do reveal significant lateral variability in Q structure. The inferred attenuation variability corresponds to the heat-flow variations within the geothermal region. A central low-Q region corresponds well with the central high-heat flow region; additional detailed structure is also suggested.

Item Type:Article
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Hough, S. E.0000-0002-5980-2986
Additional Information:© 1999, by the Seismological Society of America. Manuscript received 15 April 1999. We thank Joan Gomberg, Steve Hartzell, Mike Fehler, and two anonymous reviewers for helpful comments and suggestions; we thank Peter Malin for data and valuable comments, The authors thank the Navy Geothermal Program for funding J. Lees' efforts on this project (Awards N68936-94-R-0139 and N68936-97-C-0001), We further acknowledge CalEnergy Co. Inc. for making available their data, Figure 1 was generated using GMT software (Wessel and Smith, 1991); Figures 9a and 9b were generated using Xmap8 (Lees, 1995).
Funding AgencyGrant Number
Navy Geothermal ProgramN68936-94-R-0139
Navy Geothermal ProgramN68936-97-C-0001
Issue or Number:6
Record Number:CaltechAUTHORS:20140806-153550881
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Official Citation:S. E. Hough, J. M. Lees, and F. Monastero Attenuation and source properties at the Coso Geothermal Area, California Bulletin of the Seismological Society of America, December 1999, v. 89, p. 1606-1619
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:48141
Deposited By: Ruth Sustaita
Deposited On:06 Aug 2014 22:55
Last Modified:09 Mar 2020 13:18

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