Satellite observations of surface deformation at the Coso Geothermal Field, California

Abstract

Surface deformation time series and rates are identified at the Coso Geothermal Field (CGF) and surrounding areas by applying interferometric synthetic aperture radar (InSAR) to satellite scenes from Envisat (June 2004 ̶ October 2010) and Sentinel (November 2014 – April 2018). The measurements are done in the line of sight (LOS) to each satellite, within an area of size ~450 km2, at the locations of hundreds of thousands permanent and distributed scatterers. Thirty descending (satellite moves north to south) and 45 ascending (south to north) images were used from Envisat, and 63 descending and 65 ascending from Sentinel. A decomposition into average vertical and east horizontal components is also performed in more than 35,000 100-m pixels where both types of LOS measurements are available. The main observations at CGF include: (1) a subsidence area of size ~70 km2, with a maximum subsidence of –27.6 mm/year for the Envisat period and lower maximum subsidence of –19.1 mm/year for the Sentinel period; (2) eastward movements in the western part of the subsidence area, with Envisat maximum of +23.9 mm/year and a lower Sentinel maximum of +15.9 mm/year; (3) westward displacements in the eastern part of the subsidence area, with Envisat maximum of ̶ 14.2 mm/year and Sentinel maximum of –11.9 mm/year; (4) very good agreement of the InSAR observations with leveling survey data; (5) earthquake clusters in the subsidence area and hypocentral cross-sections showing clusters at various depths and migration in time; and (6) good predictions of the overall geothermal resource, based on poroelastic modeling using both leveling and InSAR data. The ultimate goal of the project is to provide geothermal operators with tools that can be used in reservoir management.