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Journal Article

A new gravity interpretation: A case study from Pahute Mesa, Nevada test site

K. Mallick, V. K. Rao and K. K. Sharma
Current Science
Vol. 76, No. 11 (10 June 1999), pp. 1495-1498
Stable URL: http://www.jstor.org/stable/24101426
Page Count: 4
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Abstract

The separation of regional and residual components from observed Bouguer gravity anomaly is crucial in gravity intepretation. A new approach is applied in this study to compute the residual anomaly of the Pahute Mesa region lying on the north-west corner of Nevada test site. The drilling in Pahute Mesa revealed a structural depression, which in fact, is a caldera, known as Silent Canyon. This region is topographically very high (> 2000 m) and yet the lowest gravity values (∼- 220 mGal) are observed here. This appears to be an exceptional case in the Nevada test site. Geologically, the low-density Cenozoic sedimentary and volcanic rocks in the Silent Canyon overlie the denser pre-Cenozoic basement. The thickness of the top sedimentary and volcanic rocks needs to be redefined for the conduction of nuclear tests. The basement depth determination by a previous USGS study in the Pahute Mesa region appears to be inconclusive. The basement thickness was predicted to be 7000 ft, whereas the drilll hole UE 20f in the central region up to a depth of 13,686 ft did not encounter the basement rocks. In sharp contrast, the thickness of the Cenozic sedimentary and volcanic sequences not too far from the drill hole UE 20f in the Silent Canyon, was estimated to be 17,000 ft by interpreting residual gravity anomaly obtained by our new approach, based on the finite element concept. This depth estimate seems to be geologically more realistic. The basement configuration of the Pahute Mesa site has been constructed by interpreting a number of residual gravity profiles.

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