Electrical and seismic properties of the Earth's crust in the southwestern Great Plains of the U.S.A

Data from 20 magnetotelluric stations were used to determine a resistivity-depth distribution for the crust in western Texas. We computed one-dimensional models, which adequately explained the apparent resistivities obtained from the elements of a rotated impedance tensor. Descriptions of the method of data processing and model computation are given. The derived model includes an anisotropic, low resistivity layer at depths slightly greater than 20 km. The resistivity model is compared with a seismic velocity interpretation for eastern New Mexico, and the low resistivity layer is inferred to coincide with a zone of low seismic velocity. The base of the low velocity-low resistivity region occurs at the transition from intermediate to more basic rocks in the crust. The low resistivity values are interpreted as resulting from interstitial fluid. This fluid may cause low seismic velocities and may form a weak region in which continental earthquakes occur. Interstitial water at depth in the crust may be produced by the intersection of the crustal temperature-depth curve and equilibrium boundaries of hydrothermal reactions.