Deep Vs Profiling Along the Top of Yucca Mountain Using a Vibroseis Source and Surface Waves
Yucca Mountain, Nevada, was approved as the site for development of the geologic repository for high-level radioactive waste and spent nuclear fuel in the United States. The U.S. Department of Energy has been conducting studies to characterize the site and assess its future performance as a geologic repository. As part of these studies, a program of deep seismic profiling, to depths of 200 m, was conducted along the top of Yucca Mountain to evaluate the shear-wave velocity (V{sub s}) structure of the repository block. The resulting V{sub s} data were used as input into the development of ground motions for the preclosure seismic design of the repository and for postclosure performance assessment. The noninvasive spectral-analysis-of-surface-waves (SASW) method was employed in the deep profiling. Field measurements involved the use of a modified Vibroseis as the seismic source. The modifications allowed the Vibroseis to be controlled by a signal analyzer so that slow frequency sweeps could be performed while simultaneous narrow-band filtering was performed on the receiver outputs. This process optimized input energy from the source and signal analysis of the receiver outputs. Six deep V{sub s} profiles and five intermediate-depth (about 100 m) profiles were performed along the top of Yucca Mountain over a distance of about 5 km. In addition, eleven shallower profiles (averaging about 45-m deep) were measured using a bulldozer source. The shallower profiles were used to augment the deeper profiles and to evaluate further the near-surface velocity structure. The V{sub s} profiles exhibit a strong velocity gradient within 5 m of the surface, with the mean V{sub s} value more than doubling. Below this depth, V{sub s} gradually increases from a mean value of about 900 to 1000 m/s at a depth of 150 m. Between the depths of 150 and 210 m, V{sub s} increases more rapidly to about 1350 m/s, but this trend is based on limited data. At depths less than 50 m, anisotropy in V{sub s} was measured for surveys conducted parallel and perpendicular to the mountain crest, with the velocity parallel to the crest about 200 m/s higher. In the 5- to 50-m depth range, the average coefficient of variation (COV) of all data is about 0.25. Below 75 m, where the data set is smaller and includes measurements only parallel to the crest, the average COV decreases to a value of about 0.11.
- Research Organization:
- Yucca Mountain Project, Las Vegas, NV (United States)
- Sponsoring Organization:
- US Department of Energy (US)
- OSTI ID:
- 837494
- Resource Relation:
- Conference: 13th World Conference on Earthquake Engineering, Vancouver, British Columbia (CA), 08/01/2004--08/06/2004; Other Information: Paper No. 538; PBD: 16 Mar 2004
- Country of Publication:
- United States
- Language:
- English
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