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Micro-seismicity within the Coso Geothermal field, California, from 1996-2012

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Abstract

We extend our previous catalog of seismicity within the Coso Geothermal field by adding over two and a half years of additional data to prior results. In total, we locate over 16 years of seismicity spanning from April 1996 to May of 2012 using a refined velocity model, apply it to all events and utilize differential travel times in relocations to improve the accuracy of event locations. The improved locations elucidate major structural features within the reservoir that we interpret to be faults that contribute to heat and fluid flow within the reservoir. Much of the relocated seismicity remains diffuse between these major structural features, suggesting that a large volume of accessible and distributed fracture porosity is maintained within the geothermal reservoir through ongoing brittle failure. We further track changes in b value and seismic moment release within the reservoir as a whole through time. We find that b values decrease significantly during 2009 and 2010, coincident with the occurrence of a greater number of moderate magnitude earthquakes (3.0 ≤ ML < 4.5). Analysis of spatial variations in seismic moment release between years reveals that localized seismicity tends to spread from regions of high moment release into regions with previously low moment release, akin to aftershock sequences. These results indicate that the Coso reservoir is comprised of a network of fractures at a variety of spatial scales that evolves dynamically over time, with progressive changes in characteristics of microseismicity and inferred fractures and faults that are only evident from a long period of seismic monitoring analyzed using self-consistent methods.

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Additional publication details

Publication type Conference Paper
Publication Subtype Conference Paper
Title Micro-seismicity within the Coso Geothermal field, California, from 1996-2012
Year Published 2017
Language English
Publisher Stanford University
Contributing office(s) Earthquake Science Center
Description 10 p.
Larger Work Title Proceedings, Thirty-Eighth Workshop on Geothermal Reservoir Engineering
Conference Title Thirty-Eighth Workshop on Geothermal Reservoir Engineering
Conference Location Stanford, California
Conference Date February 11-13, 2013
Country United States
State California
Other Geospatial Coso Geothermal Field