Seismicity Studies in the Region of the Cerro Prieto Geothermal Field

Abstract

We report results from seismicity studies in the region of the Cerro Prieto Geothermal Field. These studies were conducted with local short period seismic arrays during 1974-75 and 1977-78. During the latter period, horizontal seismometers were used for better control on the S-wave arrival times. Locations were obtained for about 200 events and composite fault plane solutions were obtained for five groups of events. The seismic activity is characterized primarily by swarms of relatively small events, although one swarm had events with magnitudes as high as 5.0.
The epicenters indicate a broad distribution connecting the Cerro Prieto and Imperial faults. Within this distribution there are indications of trends both parallel to and oblique to the Cerro Prieto-Imperial transform fault system. The composite fault plane solutions indicate right lateral strike-slip faulting along NW-SE trending faults and dip-slip faulting along at least some of the oblique faults.
The results are consistent with the model proposed by Hill (1977) and suggest that swarms occur as a result of injection of magmatic fluids along fault zones. Thus understanding the nature of faulting and tectonic processes is very important in evaluating the potential for geothermal energy in a region.