Analysis of subsurface structures based on seismic and gravimetric exploration methods in the Las Tres Virgenes volcanic complex and geothermal field, Baja California Sur, Mexico

摘要

Las Tres V?rgenes Geothermal Field (LTVGF) is located in the northern flank of the Volcanic Complex (LTVVC) of the same name. The area sits on the northeast part of Baja California Sur, Mexico. The LTVGF is one of five active geothermal fields in the country. It started producing electrical energy in 2001 and currently has an installed capacity of 10 MW. The fluids in the geothermal field circulate through faults and fractures that cut and transect the Cretaceous granodioritic basement and uppermost sedimentary and volcanic rocks. This study presents new seismic (controlled source) and gravimetric models to characterize the structural system of the volcanic complex, its relationship with the movement of geothermal fluids, and the location of new areas with geothermal potential. The seismic sections were correlated with lithological columns from geothermal drill hole. The multichannel analysis of surface waves (MASW) method was used to characterize the shallow (60 m) subsurface structure of the complex and two seismic reflection profiles were used to identify deeper structures. The analysis of 223 gravimetric stations and anomaly maps allowed the identification of a new fault system. Based on the gravimetric anomalies, surface geology, and lithostratigraphy of CFE wells, four two-dimensional (2D) models were constructed. In these models, the spatial distribution of the main lithological units beneath the volcanic complex as well as a fault system can be observed. Finally, the integrated results show new areas of potential interest located within the Las Tres V?rgenes Volcanic Complex and a geothermal field.