Introduction Nuclear weapons are integral to the defense of the United States.
The U.S. Department of Energy, as the steward of these devices, must
continue to gauge the efficacy of the individual weapons. This could
be accomplished by occasional testing at the Nevada Test Site (NTS) in
Nevada, northwest of Las Vegas. Yucca Flat Basin is one of the testing
areas at the NTS. One issue of concern is the nature of the somewhat
poorly constrained pre-Tertiary geology and its effects on ground-water
flow in the area subsequent to a nuclear test. Ground-water modelers
would like to know more about the hydrostratigraphy and geologic structure
to support a hydrostratigraphic framework model that is under development
for the Yucca Flat Corrective Action Unit (CAU).
During 2003, the U.S. Geological Survey (USGS) collected and processed Magnetotelluric
(MT) and Audio-magnetotelluric (AMT) data at the Nevada Test Site in
and near Yucca Flat to help characterize this pre-Tertiary geology. That
work will help to define the character, thickness, and lateral extent
of pre-Tertiary confining units. In particular, a major goal has been
to define the upper clastic confining unit (UCCU) in the Yucca Flat area.
Interpretation will include a three-dimensional (3-D) character analysis
and two-dimensional (2-D) resistivity model. The purpose of this report
is to release the MT sounding data for north central Yucca Flat, Profile
7, as shown in Figure 1. No interpretation of the data is included here.