| Abstract: |
Surface deformation in the Salton Sea geothermal field is modeled using results from satellite radar interferometry, data from leveling surveys, and observations from the regional GPS network. The field is located in the Salton Trough, an active spreading center in southern California, which is traversed by the Brawley seismic zone. Deformation time series at thousands of points in the study area are obtained from a PSInSARTM (permanent scatterers interferometric synthetic aperture radar) analysis of two-year Radarsat satellite data covering the period May 2006 - March 2008. SAR scenes from two orbit geometries are used, descending and ascending, which makes it possible to convert the deformation rates obtained in the line-of-sight (LOS) to the satellite, into vertical and horizontal components. These are further interpolated to model the surface deformation rates throughout the field. The results are constrained with ground-based leveling observations. Two main subsidence areas are observed in the geothermal field, with maximum vertical and horizontal deformation rates of up to 30 mm/year, relative to a reference point on Obsidian Butte, less than 5 km away. Comparisons are also made with the time series of production and injection fluid, as well as with seismicity. No simple spatial connection between the areas of maximum subsidence, locations of wells, and seismicity is found. It is estimated that the regional tectonic contribution to the maximum deformation rates in the field is at most 10%. The remainder may be accommodated to a large extent by the local tectonics, as there are arguments that the geothermal operations do not contribute significantly to surface deformation. In the absence of surface expression of faults in the study area, these effects cannot be properly estimated at this time. An ongoing analysis of seismicity is intended to partially address this uncertainty. |