Deviatoric Moment Tensor Analysis at The Geysers Geothermal Field

Abstract

We have determined source parameters and a complete analysis of uncertainties for three M4+ earthquakes at The Geysers geothermal field using a regional moment tensor method. We invert three-component, complete waveform data from broadband stations of the Berkeley Digital Seismic Network for deviatoric and full, six-element moment tensors. The stability of the moment tensor solutions is investigated to assess the significance of the non-double-couple terms. The solutions are presented together with estimates of errors due to imperfect station coverage and limited knowledge of the velocity structure. Preliminary results indicate that one event has a somewhat significant (F-Test) isotropic component that appears to be stable and suggestive of fluid or gas involvement during the rupture process, however sensitivity tests indicate that the most likely solution is a non-volumetric nondouble- couple solution. This initial analysis defines the framework with which we will determine and review moment tensor solutions for M>3 seismicity occurring in the region.