HR: 1400h
AN: G33A-04    [Abstracts]
TI: Aseismic Slip Observed on the Faults in Mexicali Valley, Baja California, Mexico.
AU: * Glowacka, E
EM: glowacka@cicese.mx
AF: CICESE, Sismologia, km 107 carretera Tijuana-Ensenada, Ensenada, BC 22860, Mexico
AU: Sarychikhina, O
AF: CICESE, Sismologia, km 107 carretera Tijuana-Ensenada, Ensenada, BC 22860, Mexico
AU: Suarez, F
AF: CICESE, Geologia, km 107 carretera Tijuana-Ensenada, Ensenada, BC 22860, Mexico
AU: Nava, F
AF: CICESE, Sismologia, km 107 carretera Tijuana-Ensenada, Ensenada, BC 22860, Mexico
AU: Farfan, F
AF: CICESE, Sismologia, km 107 carretera Tijuana-Ensenada, Ensenada, BC 22860, Mexico
AU: Cossio Battani, G D
AF: CICESE, Sismologia, km 107 carretera Tijuana-Ensenada, Ensenada, BC 22860, Mexico
AU: Guzman, M
AF: CICESE, Sismologia, km 107 carretera Tijuana-Ensenada, Ensenada, BC 22860, Mexico
AU: Guzman, M
AF: UABC, Escuela de Ingenieria, Justo Sierra, Mexicali, BC , Mexico
AB: The Mexicali Valley, which is part of the Salton Trough, is located within an active tectonic region, in the boundary between the Pacific and North American plates; a region featuring a wide zone of transform faults associated with San Andreas fault system, and a zone of distributed deformation in the pull-apart center of Cerro Prieto. 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. The mainly vertical displacement at Saltillo fault (known before as southernmost part of Imperial fault) has been measured on a continuous basis since February 1996 by a crackmeter installed in Ejido Saltillo (Glowacka 1996; Nava and Glowacka, 1999). In 1998 a tiltmeter was installed on the fault and a second crackmeter , in a horizontal direction, about 60° from the fault strike, was installed about 1 km south of ES. Another crackmeter in the vertical plane crossing Morelia fault and a 3D Witness on the Cerro Prieto fault were installed in 2004. In 2003 seven digital water level meters were installed at depths up to 500 meters in the local piezometric wells, with the purpose of recording aquifer level changes. The observed deformation rates measured on the Saltillo fault are 6 cm/yr and 2 cm/yr for the vertical and horizontal components, respectively and occurs in steps (creep events), separated by months of quiescence, and large events account for 70 percent of the vertical displacement. Aseismic creep events have amplitudes of 1-3 cm and durations of 1-3 days. Much less precise measurements from the Cerro Prieto fault show vertical deformation on the fault with velocity around 3.1 cm/yr , and the rate does not depend on the local seismicity. Horizontal rates change slightly with the presence of seismicity when very small right lateral deformation (few mm/yr) can be observed. From the delay measured on different instruments installed on the Saltillo fault one can conclude that creep events have an apparent migration velocity of the order of 4 cm/s. Comparison between occurrence of creep events and the water level record done for the piezometer installed nearby, shows that in four cases a water level anomaly is associated with a creep event. We discuss some possible relation between creep phenomenon and water level changes, and tectonics, geology and anthropogenic activity in the Mexicali Valley. This research is sponsored partly by the CONACYT project 45997-F.
DE: 1207 Transient deformation (6924, 7230, 7240)
DE: 7215 Earthquake source observations (1240)
SC: Geodesy [G]
MN: 2007 Joint Assembly