A decade of geodetic deformation linked to fluid injection at the North Brawley Geothermal Field

Abstract:

The North Brawley Geothermal Field, located within the Brawley Seismic Zone of Southern California, has utilized binary cycle power generation to produce more than 30 MWe since 2009. The field has been associated with both aseismic ground deformation and seismic activity, including an earthquake swarm in 2012 that resulted in two earthquakes with magnitude greater than 5. To better understand this ground deformation and its causative mechanisms, we construct a comprehensive deformation time series using multiple ground- and satellite-based geodetic techniques between 2009 and 2019. We integrate observations from GNSS, Sentinel-1, TerrSAR-X, UAVSAR, and leveling surveys into a single deformation history. We then test models of aseismic slip and/or poroelastic deformation using a time-dependent slip inversion technique based on the small baseline subset (SBAS) method in InSAR processing. We find evidence for both aseismic slip on known fault structures and other sources of deformation during the last decade, with some of these episodes not previously identified. Anomalous transient signals at several GNSS stations are particularly difficult to reconcile with the InSAR and leveling observations and suggest an unusual source mechanism. We then compare the deformation history with injection and production parameters and seismicity catalogs. This long-term deformation history allows us to probe the geothermal field’s behavior in the presence of both long-term and short-term temporal changes in operational parameters, which has implications for other geothermal operations around the world.