Magnetotelluric Models of the Roosevelt Hot Springs Thermal Area, Utah

Philip E. Wannamaker
Stanley H. Ward
Gerald W. Hohmann
William R. Sill

DOE/ET/27002-8 Prepared for the U.S. Department of Energy, Assistant Secretary for Energy Technology, Division of Geothermal Energy


The Roosevelt Hot Springs (RHS) thermal area, which includes a hot-water-dominated fracture zone prospect, near the eastern margin of the Basin-Range tectonic province, conceivably possesses a whole family of resistivity structures that includes the following: deep hot brine reservoirs, deep-seated partially molten heat sources in the crust or upper mantle that drive the convective system, near-surface hydrothermal alteration zones, wet sedimentary fill in valleys, and a regional, apparently one-dimensional resistivity profile of the crust and upper mantle. This complex resistivity makeup, particular to RHS but probably similar to that at other geothermal areas in the Great Basin, must be treated as being fully three-dimensional (3-D). In an attempt to understand these structures, we have obtained broadband (10 -3 to 10 2 Hz) tensor magnetotelluric (MT) data including apparent resistivities, impedance phases and vertical magnetic field transfer functions for 93 sites in the vicinity of this resource area.