Documenting surface deformation at the first geothermal power plant in South America (Cerro Pabellón, Chile) by satellite InSAR time-series

Abstract

In 2017, Cerro Pabellón in northern Chile became the first high-enthalpy geothermal power facility to go into service in South America. We evaluated Interferometric Synthetic Aperture Radar (InSAR) data containing 201 SAR scenes from the Sentinel-1A/B satellite mission between 2014 and 2021 to quantify the time-dependent surface deformation in the vicinity of the Cerro Pabellón geothermal plant. Using ascending and descending satellite orbits and the InSAR small baseline subset (SBAS) approach, we detected subsidence rates up to 6.3 mm/yr along the line of sight near the geothermal area, which began in 2017 and persisted through 2020 at which time the deformation rate decreased. We believe that geothermal activity may be responsible for the observed deformation based on the timing of the deformation – there was no detectable deformation in the area until the start of operations of the power plant. We invert the source of ground deformation using multiple analytic elastic half-space models (one or more spheroi ds or a sill-like source). The depth of the inferred sources is between 370 and 660 meters and is similar to the depth of the reservoir as determined by surface geophysics and well data. InSAR time series have not yet detected any tectonic deformation on the faults that encircle the graben where the geothermal plant is located, nor at the graben’s periphery. While the seismic records from a regional network near the geothermal field, analyzed between March 2017 and August 2020, show microseismicity in the graben near the power plant, accurate positions cannot be computed due to sparse and inadequate seismic data. Therefore, any possible correlation between the observed seismicity and the geothermal operations remains uncertain. This study emphasizes the need for an improved seismic network to obtain a better understanding of the geothermal-tectonic interplay.