Attenuation and source properties at the Coso Geothermal area, California

S. E. Hough; J.M. Lees; F. Monastero

doi:10.1785/bssa0890061606

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Attenuation and source properties at the Coso Geothermal area, California

S. E. Hough·J.M. Lees·F. Monastero

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Abstract

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.

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Bulletin of the Seismological Society of America Article

Source-reported bounding extent: 36.02074657364588° to 36.39650466586174° latitude; -118.06387845545854° to -117.54128968837821° longitude. This indicates report coverage, not an exact sampling location. View area on OpenStreetMap.

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BibTeX RIS

S. E. Hough, J.M. Lees, F. Monastero. 1999-12-01. Attenuation and source properties at the Coso Geothermal area, California. https://doi.org/10.1785/bssa0890061606

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