Geophysical Investigations at Pahute Mesa, Nevada

The seismic response of underground nuclear explosion tests at Pahute Mesa, NV displays variations which correlate with the geologic/geophysical structure. Investigations have been performed using borehole, gravity and wide angle seismic observations, with the aim of producing a geophysical model of the Silent Canyon caldera structure at Pahute Mesa. Empirical models of the density and seismic velocity have been formulated based on well logs. New gravity stations were obtained in 1985 and merged with older, lower quality data. A new gravity modeling technique was developed and applied to the modeling of a transect across the area. The resulting model supports the hypothesis that a high density and velocity blanket at a depth of a few kilometers. In 1986 a wide angle seismic reflection/refraction survey was completed near the gravity profile. The 15 km long line crossed the buried caldera boundary as well as important normal faults. The shot point was located on outcropping basement. Future interpretation of the combined gravity and seismic data should permit the construction of a predictive geophysical model. Keywords: Structural geology, Gravity modeling; Seismic exploration at Nevada test site.