Geological Survey investigations in connection with the Mighty Epic event, U12n. 10 tunnel, Nevada Test Site
The Might Epic event was executed 396 m (1300 ft) beneath the surface of Rainier Mesa in U12n.10 tunnel at the Nevada Test Site. The tunnel complex consists of two subparallel 609-m- (2000-ft) long northwest-trending drifts and various experimental drifts, totaling approximately 1675 m (5500 ft). Fourteen exploratory drill holes were also evaluated in conjunction with the assessment of the Mighty Epic site. The rocks penetrated by the drifts are zeolitized tuffs of tunnel bed units 2 to 4 and the Tub Spring Member of the Belted Range Tuff, all of Miocene age. No zones of intense argillization were logged in the drill holes or mapped in the drifts. The bedding dips from 12/sup 0/ to 20/sup 0/, increasing toward the northwest. The axis of a south-plunging ridge, developed on the pre-Tertiary surface, is located within 58 m (190 ft) of the working point. Differential compaction and slumping over this ridge is thought to be the cause of a high frequency of fractures near the working point. The closely spaced fractures are generally coated with a black calcium manganese oxide, which was probably precipitated in a near-surface desert environment during Miocene time. A fault scarp, on the pre-Tertiary surface, which has approximately 46 m (150 ft) of relief is located 152 m (500 ft) east of the working point. No evidence of this fault is seen at tunnel level, and therefore, it is assumed to be pre-Tertiary in age. Only 4 of the 34 faults mapped in the U12n.10 bypass drift are thought to extend to or near to the mesa surface. All faults mapped in the U12n.10 complex are considered tight and dry.
- Research Organization:
- Geological Survey, Denver, CO (USA)
- DOE Contract Number:
- AI08-76DP00474
- OSTI ID:
- 6609859
- Report Number(s):
- USGS-474-228; ON: DE83005513
- Country of Publication:
- United States
- Language:
- English
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