| Title | Fluid Imaging, Moment Tensors and Finite Source Models at the EGS Demonstration Project at the Geysers, CA |
|---|---|
| Authors | Roland GRITTO, Douglas S. DREGER, O. Sierra BOYD and Taka'aki TAIRA |
| Year | 2016 |
| Conference | Stanford Geothermal Workshop |
| Keywords | EGS development, fracture characterization, moment tensor, finite-source, Vp/Vs ratio |
| Abstract | We investigate seismicity in the vicinity of the EGS development at The Geysers Prati-32 injection well. The goals of our study include the ability to estimate the activated fracture area and volume, to estimate stress drop and stress drop changes as well as fluid saturation and temporal changes in fluid distribution. For this paper we have incorporated the capability of simultaneously inverting full waveform data and P-wave polarities to improve estimates of the source mechanism of small events. We have analyzed the full moment tensor of more than 80 events (M more than ~1.0) using a semi-automated approach, and have investigated finite-source models of five Geysers events ranging in magnitude from M 3.7 to 4.5. We find that combination of first-motion and waveforms from the Lawrence Berkeley National Laboratory (LBNL) network results in solutions for some events having positive isotropic or volume increase components. Other events appear to be predominantly double-couples. Ongoing work is examining the temporal evolution of the moment tensors during the injection process. The finite-source scaling relationship between rupture area and moment magnitude, found for the investigated events at The Geysers, resembles that of a published empirical relationship derived for field and aftershock data for events from M 4.5 to 8.3. In order to perform temporal analysis of the subsurface water saturation, we compiled and analyzed seismicity catalogs recorded by the LBNL seismic network for the area around the EGS development project. The data are analyzed using the double-difference Wadati method. |