%A Gisela Viegas
%A Lawrence Hutchings
%J Geothermal Resources Council Transactions
%T Source Characteristics of Micro-Earthquakes at the Northwest Geysers Geothermal Field, California
%X We investigate the source parameters of micro-earthquakes (<M3) at the Northwest Geysers, near an injection well, before and during water injection, looking for temporal and spatial variations. Our objective is to understand the relation among injection, production and source mechanisms of micro-earthquakes. To determine the source parameters of the micro-earthquakes, such as fault radius, stress drop, seismic moment and radiated energy, we use two techniques: the Empirical Green’s Function (EGF) method; and the NetMoment method, and compare the source parameters results of micro-earthquakes used in both studies. Our results indicate that micro-earthquakes at the Northwest Geysers have on average small radius and large stress drops (median of 27.7 MPa). The stress drops of these induced micro-earthquakes are comparable to the ones of deeper, large (>M5.5), natural occurring tectonic earthquakes. Possible explanations for the high stress drop are, for example, fault re-strengthening by geochemical alteration or the fracturing of intact rock induced by the injection of cold water. This source information has implications for understanding the physics of faulting and for seismic potential assessment in areas of ongoing geothermal exploration.
%K Geysers, micro-earthquakes, induced seismicity, earthquake source, stress drop, radiated energy, Empirical Green’s function
%P 1265-1272
%V 34
%D 2010
%I Geothermal Resources Council
%L epos1841