Time-dependent three dimensional P-wave velocity models derived for the Geysers geothermal field
Abstract
The Geysers geothermal field is a source of significant small earthquake (M< 2.0) seismicity in northern California. The region has been actively monitored for seismicity, both natural and induced, since the geothermal field has been put into production. A modern digital seismic monitoring network in the area consists of 34 LBNL/Calpine (BG) borehole short-period and 12 Northern California Seismic Network (NCSN) network surface short-period seismic stations. The USGS has auto-located approximately 25,033 earthquakes (NCEDC catalog) for the years 2009 and 2010 combined from the composite seismic network. Using the auto-located solutions and a Geysers specific one-dimensional velocity model (Eberhart-Philips and Oppenheimer, 1984) as a starting point, we have simultaneously inverted for three dimensional P-wave velocities for each year's data set. Before beginning the inversion we established that the automatic S-phase picks were too unstable and thus focused only on the P-wave velocities. After culling events with initial RMS uncertainty greater than 0.06 seconds, we start with 7,403 earthquakes in 2009 and 11,199 earthquakes in 2010. The technique we use is a finite-difference travel time technique that Roecker et al. (Tectonophysics, 2006) used for the Parkfield SAFOD site. We will present the results of the simultaneous inversion for each of the 2009 and 2010 years along with plots of the seismicity relocated using these new velocity models.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFM.S33A2312F
- Keywords:
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- 7230 SEISMOLOGY / Seismicity and tectonics