A 3-DIMENSIONAL MAGNETOTELLURIC INVESTIGATION OF THE CALIFORNIA BASINAND RANGE

Band-limited magnetotelluric measurements were collected at several si tes across a wide area in the California Basin and Range and northern Mojave Desert from early 1988 until March 1989. Due to the large spaci ng between sites and the limited frequency range of the data, there ar e limits to what the data can resolve. However, a three-dimensional (3 -D) magnetotelluric modeling study and sensitivity analysis of a subse t of the data support the following conclusions. (1) Electrical curren ts from the Pacific Ocean are channelled across the western Mojave Des ert and into the southern Basin and Range. (2) The 3-D geometry of the basins significantly influences the fit to the data mode aligned alon g the strike of the basins (transverse electric mode). (3) The lower c rust in the California Basin and Range is more conductive than the low er crust under the Mojave Desert and Pacific Ocean. The resistivity va lues we modeled for the lower crust in the California Basin and Range, though inconsistent with mineral semiconduction, can be explained by electrical conduction through small amounts of saline fluids.