| Authors |
Glowacka, Ewa; Sarychikhina, O.; Suarez, F.; Nava, A.; Farfan, F.; Batani, G. Diaz de Cossio; Garcia, A.; Guzman, M. |
| Abstract |
Since 1973, fluid extraction at the Cerro Prieto Geothermal Field (CPGF) has influenced deformation in the CPGF area, accelerating the subsidence and slip on the tectonic faults. Subsidence and fault rupture are causing damage to infrastructure, like roads, railroad tracks, irrigation channels, and agricultural fields. Detailed field mapping done since 1989 in the vicinity of the CPGF shows that many subsidence induced fractures, fissures, collapse features, small grabens and vertical displacements are related to the known tectonic faults. The affected area is localized between the Cerro Prieto and Morelia faults to the NW, and the Imperial and Saltillo faults to the SE, which limit the Cerro Prieto pull apart basin. Since 1996, geotechnical instruments have operated in the Mexicali Valley, for continuous recording of deformation phenomena. To date, the network includes three crackmeters and eight tiltmeters; all instruments have sampling intervals in the 1 to 20 minutes range. We used published leveling data and InSAR images to evaluate magnitude and the effects of the subsidence. The subsidence area is bounded by tectonic faults, as evidenced along the Saltillo fault. During the last few years the subsidence rate increased over the whole area, but this increase was significantly larger towards the NE, at the eastern subsidence basin, located outside of the CPGF. Vertical slip on the Saltillo fault, which corresponds to about half of the total subsidence, occurs mainly during slip events. The vertical slip rate on the fault increased from 5.3 cm/year to 7.3 cm/ year around the second half of 2003. The distance versus time relation between changes in extraction at the CPGF and displacement rate changes on the Saltillo fault suggests that the fault is affected by extraction through diffusive transmission of pore pressure changes, with a characteristic hydraulic diffusivity. |