Geophysical Unit of Menlo Park, Calif.

In Cooperation with the Southern Nevada Water Authority (SNWA)

U.S. Geological Survey
Open-File Report 2008-1301
Version 1.0

Audiomagnetotelluric Data and Preliminary Two-Dimensional Models from Spring, Dry Lake, and Delamar Valleys, Nevada

By Darcy K. McPhee, Bruce A. Chuchel, and Louise Pellerin

2008

map showing that the study area extends from the Schell Creek Range in the northwest to Hamlin Valley in the southeast.  The southern Snake Range (Great Basin National Park) is in the east
Topographic map of southern Spring Valley, Nev., showing location of audiomagnetotelluric profiles in red. Profiles shown in blue were collected prior to May 2007 and are presented in McPhee and others, 2006, 2007 (from figure 1)

This report presents audiomagnetotelluric (AMT) data along fourteen profiles in Spring, Delamar, and Dry Lake Valleys, and the corresponding preliminary two-dimensional (2-D) inverse models. The AMT method is a valuable tool for estimating the electrical resistivity of the Earth over depth ranges from a few meters to less than one kilometer, and it is important for revealing subsurface structure and stratigraphy within the Basin and Range province of eastern Nevada, which can be used to define the geohydrologic framework of the region. We collected AMT data by using the Geometrics StrataGem EH4 system. Profiles were 0.7 - 3.2 km in length with station spacing of 50-400 m. Data were recorded in a coordinate system parallel to and perpendicular to the regional geologic-strike direction with Z positive down. We show AMT station locations, sounding curves of apparent resistivity, phase, and coherency, and 2-D models of subsurface resistivity along the profiles. The 2-D inverse models are computed from the transverse electric (TE), transverse magnetic (TM), and TE+TM mode data by using a conjugate gradient, finite-difference method. Preliminary interpretation of the 2-D models defines the structural framework of the basins and the resistivity contrasts between alluvial basin-fill, volcanic units, and carbonate basement rocks.


Download the text of this report as a 59-page PDF file (of2008-1301_text.pdf; 4.7 MB).

Download Appendix A of this report as a 44-page PDF file. This file consists of the sounding curves (of2008-1301_appendix_a.pdf; 4.3 MB).

For questions about the content of this report, contact Darcy McPhee

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