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Core Research Areas

Field Campaigns

Dixie Valley, NV, contains a classic Basin-Range geothermal system which is currently producing and has been the subject of substantial research. Under new funding from DOE/OGWT, we will be undertaking detailed MT surveying of the system for two main purposes.

First, we wish to assess whether lateral permeability variations known to exist in the system can be mapped with useful accuracy according to electrical resistivity expression. Second, current power production at Dixie Valley generates strong EM fields which interfere with the low-level natural signals we attempt to measure in the MT method. MT signals in fact were overwhelmed for sites close to the power plant and we will attempt to overcome this using multi-transfer function methods we are developing. An initial transect of sites has been acquired across Dixie Valley and the Stillwater Range for background control in the upcoming, contiguous bipole profiling.

One of our most notable successes with the MT method was in our transect across the South Island of New Zealand, an active compressional orogen. Forty-one tensor soundings, twelve of which required helicopter support in the Southern Alps, were collected under support from the U.S. National Science Foundation using the University of Utah/EGI MT system. Two inversions of the cross-strike (transverse magnetic or TM mode) data, one using our a-priori approach and the other using the damped curvature approach of Rodi and Mackie, each show a pronounced, concave-upward conductor originating in the lower crust and shallowing towards the principal forethrust (Alpine Fault) and backthrust (Forest Creek Fault) zones of the S. Alps.

Inversions including the along-strike (transverse electric or TE) data (not shown) imply strong conductivity anisotropy with the more conductive direction along strike. The conductor in interpreted to represent fluids formed by prograde metamorphism in the thickening crustal root zone, and their expulsion towards the surface in uplifting, deep crustal schist. Near-surface approaches of the conductor correspond to outcrops of Late Cenozoic-present, mesothermal gold deposits, so that MT is glimpsing the creation and transport of this globally-significant class of ore fluids in nearly real time.

We will be applying our modeling and inversion developments to MT data from the Karaha-Telega Bodas, andesite-hosted geothermal system of the Philippines. This system is transitional between classic, volcanic-hosted systems, and liquid-dominated systems. Nearby active volcanoes attest to high heat potential and partial melting at a depth ~6 km b.s.l. is inferred. Chloride waters and hydraulic underpressures indicate a sizeable vapor zone above boiling liquid. Electrical targets include structural and permeability controls, vapor zones, surrounding condensate zones, and magma. Our interpretations will be in concert with efforts at EGI in geochemistry and gravity modeling.