A Deformation Measuring Network in the Mexicali Valley, Baja California, Mexico

Abstract

The Cerro Prieto Geothermal Field (CPGF) is located in the Mexicali Valley, in northeastern Baja California, Mexico, in the northern part of a ridge-transform plate margin. The area is characterized by a high level of seismicity, hydrothermal and volcanic phenomena, and both tectonic and anthropogenic deformation. Since 1996, geotechnical instruments have operated in the Valley, for continuous recording of deformation phenomena. To date, the network includes three crackmeters, eight tiltmeters, and seven piezometers installed in the shallow aquifer; all instruments have sampling intervals in the 1 to 20 minutes range. We present the spatial distribution and installation characteristics of the instruments, as well as preliminary interpretations of some observations. The 1110tion observed at the Imperial and Cerro Prieto faults, which confine the pull-apart system including the CPGF, is mainly vertical, probably related to the subsidence. The Imperial fault slip appears mainly as slip-predictable, aseismic, creep events, related to pressure changes in the shallow aquifer. Transient and permanent deformations related to local and global seismicity are also recorded.