HR: 1340h
AN: H23A-1013    [Abstracts]
TI: Groundwater Exploration in Baja California, Mexico, Using Audiomagnetotellurics
AU: * Antonio, R
EM: rantonio@cicese.mx
AF: Centro de Investigacion Cientifica y de Educacion superior de Ensenada, km.107 Carretera Tijuana-Ensenada, Esenada, B.C 22860, Mexico
AU: Arroyo, A
EM: aarroyo@cicese.mx
AF: Centro de Investigacion Cientifica y de Educacion superior de Ensenada, km.107 Carretera Tijuana-Ensenada, Esenada, B.C 22860, Mexico
AU: Romo, J
EM: jromo@cicese.mx
AF: Centro de Investigacion Cientifica y de Educacion superior de Ensenada, km.107 Carretera Tijuana-Ensenada, Esenada, B.C 22860, Mexico
AU: Vazquez, R
EM: rvazquez@cicese.mx
AF: Centro de Investigacion Cientifica y de Educacion superior de Ensenada, km.107 Carretera Tijuana-Ensenada, Esenada, B.C 22860, Mexico
AB: Guadalupe Valley, in Ensenada B. C. Mexico, basis of the winery industry of the region, is known by their climatic attributes for vineyard cultivation. In this place, the crop growing depends totally on underground water extracted of an aquifer contained in two separate small basins. In order to estimate the depth to water level, as well as the thickness of one of these basins, we carry out a geophysical survey using audio-magnetotellurics (AMT). We carried out five profiles in a frequency range between 1 Hz and 750 kHz to estimate the electrical conductivity of the ground. We know that this physical property is enhanced by the permeability as well as by the salinity of fluids in the aquifer. In contrast, the crystalline rocks forming the basement of the basin are very bad conductors of electricity. Based on the AMT observations we construct 2-D models of the ground resistivity distribution. Our results show a clear resistivity contrast between sediments and bedrock. The sediments have resistivity values that oscillate from 40 to 100 Ohm-m, associated with lithology and/or permeability changes. Some conductive bodies (5 to 15 Ohms-m) are observed at depths shallower that 150 m, which might be caused by the presence of water with higher salinity, or alternatively, by clay lens. The bottom of the basin has resistivity values larger than 300 Ohm-m typical of the granitic rocks composing the bedrock. The spatial variation of the basement depth suggests the presence a normal fault, in agreement with a graben structure proposed in former studies.
DE: 0600 ELECTROMAGNETICS
DE: 0900 EXPLORATION GEOPHYSICS
DE: 1835 Hydrogeophysics
SC: Hydrology [H]
MN: 2007 Fall Meeting