The Effect of a Tectonic Disturbance on the Cerro Prieto Geothermal Field (B.C., Mexico)

Abstract

We propose that a spreading event took place in the Cerro Prieto area during the period 1979-1980. Four phenomena are observe4d which indicate spreading; 1) two large earthquakes, the Imperial Valley earthquake of Oct. 15 1979 and the Victoria earthquake, June 9 1980, which occurred on two adjacent transform faults, less than 8 months apart; 2) significant extension in the NW-SE spreading direction from geodetic measurements; 3) subsidence of several cm in the Cerro Prieto geothermal field, from both leveling and gravity data; 4) a thermal even in the reservoir; i.e., an abrupt increase of more than 10°C in most of the wells of the geothermal field between the time of the two earthquakes. This may indicate the movement of magma at depth. Comparison of Cerro Prieto with tectonically similar regions such as Iceland and Afar, could help our understanding of the spreading process. The thermal effect resulting form the spreading event could be major factor in lengthening the lifetime of geothermal fields associated with spreading regions.