Modeling of Subsidence in the Cerro Prieto Geothermal Field, B. C., Mexico

Abstract

The Cerro Prieto Geothermal Field (CPGF) is located in the Mexicali Valley, in the southern part of Salton Trough. This zone is characterized by high tectonic seismicity, heat flow and surface deformation, related with the tectonic regime of the zone. Besides the tectonic deformation, extraction of fluids in CPGF produces deformation of large magnitude (Glowacka et al., 1999).
In the present work we model both natural and anthropogenic components of subsidence. We model the natural component of subsidence using known data about the seismotectonic situation and the Coulomb 2.0 program (Toda et al., 1998). The resulting model shows that the subsidence due to tectonic movement constitutes approximately 4% of the observed subsidence rate.
The anthropogenic part was simulated using "tensional rectangular cracks" (Yang and Davis, 1986). Modeling was done using the Coulomb 2.0 program with a "trial and error" strategy. The resulting model for anthropogenic subsidence is based on a hydrological model of the CPGF (Halfman et al., 1984; Lippmann et al., 1991) and can explain the observed data with a RMS misfit of 0.79 cm/yr.
To evaluate the influence of deformation in the stress field and in the local seismicity, we calculated the change of the Coulomb stress produced by the closure of cracks in our model, as well as by tectonic movement. Our results show that the magnitude of this stress-field change, caused by extraction of fluids in CPGF, is large enough to trigger earthquakes.