Seismic Investigation of the Neal Hot Springs Geothermal Area

Neal Hot Springs (NHS) is an active geothermal site and home to a 23MW geothermal electric power plant that is now online and producing at full capacity. The site is located near Vale, Oregon (approx. 145 km Northwest of Boise) and consists of about 25 square kilometers of land which is leased by U.S. Geothermal Inc. In May 2011, students and faculty of the Boise State University geophysics field camp set up a network of 11 seismic stations in the area to monitor seismic activity related to geothermal production and natural seismicity. The network continuously recorded data until it was decommissioned in November 2012. The network obtained continuous seismic recordings during construction and testing of the power plant facility, and continued seismic recording during production. We are using the data to establish a datum of global, regional, and local natural seismicity and we are analyzing the data to identify seismic activity directly related to geothermal testing and production. Currently, our results show that the area surrounding Neal Hot Springs Geothermal Plant exhibits very little natural seismic activity, unusual for a geothermal system. With a nearly two year dataset, we have identified two small magnitude earthquakes within the vicinity of NHS. We have yet to establish the link between these two earthquakes and geothermal activities at NHS, but we have established that both events took place within a few kilometers of the site. Our preliminary conclusion is that these earthquakes are likely from the nearby Cottonwood Mountain fault that shows compelling evidence for late Quaternary motion. This fault is one of many northwest-trending active faults within eastern Oregon. We have not confirmed any seismic activity induced by the power plant thus far, but ongoing analysis from our May 2011 to November 2012 seismic data will help identify small seismic events near NHS that are either related to the Cottonwood Mountain fault or related to geothermal production at NHS. Our results will place constraints on local seismicity that will enable us to better understand hazards and stresses related to active faults or geothermal production