Combined analysis of surface reflection imaging and vertical seismic profiling at Yucca Mountain, Nevada Page: 3 of 53
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Introduction
This report presents results from surface and borehole seismic profiling performed by the
Lawrence Berkeley Laboratory .(LBL) on Yucca Mountain. This work was performed as part of
the site characterization effort for the potential high-level nuclear waste repository. Our objective
was to provide seismic imaging from the near surface (200 to 300 ft. depth) to the repository
horizon and below, if possible. Among the issues addressed by this seismic imaging work are
location and depth of fracturing and faulting, geologic identification of reflecting horizons, and
spatial continuity of reflecting horizons. We believe our results are generally positive, with some
specific successes. This was the first attempt at this scale using modern seismic imaging
techniques to determine geologic features on Yucca Mountain. We recognize that we still have
work to do to fully optimize the data acquisition and processing. Since previous seismic reflection
studies in the area have had mixed results with difficulty imaging coherent reflections (e.g.
Harding, 1988, McGovern, et al., 1983), we feel the data presented here is part of the learning
process for optimal application of seismic imaging methods on the Yucca Mountain site.
The principle purpose of this report is to present the interpretation of the seismic reflection
section in a geologic context. We do not intend to report on complete details of the processing
steps, sequences and techniques used. Those processing results were presented earlier in Majer
and Karageorgi, 1993, and Daley and Majer, 1993. It should be noted that the lithologic
interpretations presented in this report are only intended to be approximate and a best guess by a
seismic interpreter which may differ from the accepted lithostratigraphic model mapped by
geologists. The model derived from seismic results will not be the same as that derived from other
techniques, but it is intended to aid progress toward a single 3-D model of Yucca Mountain.
Three surface reflection profiles were acquired and processed as part of this study.
Because of environmental concerns, all three lines were on preexisting roads. The locations of the
profile lines are shown in Fig la. Figs lb - id show geologic cross-sections along the azimuth of
each line; these figures were generated using the computer-assisted lithostratigraphic model being
compiled by the U.S. Geological Survey (USGS) (USGS Rock Characteristics Section, written
communication, 1994). Line 1 crossed the mapped surface trace of the Ghost Dance fault and it
was intended to study the dip and depth extent of the fault system. Vertical seismic profile (VSP)
surveys were acquired in and around well WT-2 (which is located along surface line 1) as part of
the Ghost Dance fault imaging. " Line 2 was acquired along Drill Hole wash. VSP surveys were
acquired in well NRG-6 which is located next to line 2. The Drill Hole wash studies were intended
to help the ESF north ramp design activities. Line 3 was acquired along Yucca Crest. No VSP
studies were performed along line 3. Line 3 was designed to image geologic horizons which were
thought to be less faulted along the ridge. Unfortunately, line 3 proved to have poor data quality,
in part because of winds, poor field conditions and limited time. Because of this, Line 3 was not
interpreted as part of this report although we do provide a stacked common depth point (CDP)
section for Line 3. Our processing and interpretation efforts were focused on lines 1 and 2 and
their associated VSP studies.
Background
Geophysical characterization of the subsurface using seismic methods has three basic types
of data acquisition, surface to surface (surface reflection or refraction profiling), vertical seismic
profiling (VSP) and cross-hole seismic profiling. Before acquiring the surface seismic lines, we
had already carried out VSP at WT-2 and NRG-6, and cross-hole imaging at the C-hole complex.1
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Daley, T. M.; Majer, E. L. & Karageorgi, E. Combined analysis of surface reflection imaging and vertical seismic profiling at Yucca Mountain, Nevada, report, August 1, 1994; California. (https://digital.library.unt.edu/ark:/67531/metadc689948/m1/3/: accessed April 26, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.