Quantifying the Potential for Induced Seismicity and the Associated Hazard and Risk for EGS Projects in Nevada and Oregon

ABSTRACT As part of the development of Induced Seismicity Mitigation Plans (ISMPs) for four proposed enhanced geothermal system sites in Nevada and Oregon, we are evaluating the potential for induced and triggered seismicity and the associated seismic hazard and risk at each site in line with the seven steps described in the U.S. Department of Energy's (DOE) Protocol for Addressing Induced Seismicity Associated with Enhanced Geothermal Systems. In Step 1, preliminary screening-level risk analyses are being performed to assess the potential impacts on the local communities and stakeholders during routine operations, including a possible worst-case scenario. In Step 3, criteria for ground vibration and noise are being reviewed and selected to assess the existing ground vibration and noise environments to establish a baseline, and evaluate the anticipated impacts. In Step 5, the seismic hazard at each project site is being estimated due to both natural and induced seismicity. The former provides a baseline from which to evaluate the additional hazard that may be imposed by induced earthquakes. In Step 6, a robust estimate of the seismic risk is being developed prior to the project and associated with the stimulation. The risk analysis helps evaluate alternative operational procedures, including those that could mitigate negative effects and minimize the risk from induced seismicity. INTRODUCTION As part of the development of Induced Seismicity Mitigation Plans (ISMPs) for four proposed enhanced geothermal system (EGS) sites in Nevada and Oregon, we are (1) evaluating the potential for induced and triggered seismicity, (2) performing probabilistic seismic hazard analyses (PSHAs) that address the hazard from both natural tectonic seismicity and potential induced seismicity, and (3) evaluating the associated seismic risk at each site. The ISMPs are being developed consistent with the seven steps described in DOE's Protocol for Addressing Induced Seismicity Associated with Enhanced Geothermal Systems (Majer et al., 2012). The overarching purpose of the Protocol is to promote the safety of EGS projects and to help gain acceptance of geothermal development from the general public. The Protocol represents best practices regarding geothermal-induced seismicity and provides guidelines that should be followed to mitigate potential adverse effects from induced earthquakes.