Analysis of fault rupture potential resulting from large-scale groundwater withdrawal: application to Spring Valley, Nevada

Hydrospheric mass changes create subsurface stress perturbations on a scale that can trigger seismic events or accelerate frequency of seismicity on proximal faults. For example, groundwater pumping has been implicated in the 2011 Mw 5.1 earthquake in Lorca, Spain and the 2010 Mw 7.1 El-Mayor Cucapah earthquake in northern Baja California. Previous work on effects of pumping on seismicity is retrospective. We propose a method to assess changes in rupture potential on faults near areas of large-scale groundwater withdrawal ahead before pumping begins. Changes in potentiometric head due to pumping predicted by (MODFLOW) groundwater flow models can be used as the change in surface load input for analytical solutions from Boussinesq [1885] to resolve changes in the subsurface state of stress. Coulomb stress, which quantifies a fault’s tendency toward failure, is then resolved on proximal faults. These stress changes can be compared with a 10 kPa stress threshold developed in previous work from statistical correlation of aftershock occurrence with spatial patterns of post-seismic Coulomb stress change on surrounding faults. Stress changes on critical to near-critically stressed faults above the threshold represent a higher likelihood of seismic rupture. The method is applied to a proposed groundwater development project in Spring Valley, Nevada. Proposed pumping in excess of 50 years will result in stress change on the proximal normal fault exceeding the 10 kPa threshold. This change in Coulomb stress is in the realm of earthquake-inducing pumping. However, the low seismic hazard in the region determined from geodetic and paleo-seismic analysis does not suggest imminent rupture