A view of Lathrop Wells Cone
Photo by USGS

USGS geologists studied seismic and volcanic hazards at Yucca Mountain to evaluate the probabilities of recurrence for volcanic eruptions and earthquakes of various magnitudes at or near Yucca Mountain. The depositional and deformational histories of Yucca Mountain were used in a probabilistic seismic hazards analysis (PSHA) and a probabilistic volcanic hazards analysis (PVHA).

Seismic hazards studies were based on logging and interpretation of trenches across faults, which showed evidence of movement within the past million years and in some cases the past few thousand years, at and near Yucca Mountain. The trench analyses provided a detailed history of dated fault displacements and the evidence of surface-rupturing earthquakes.

Volcanic eruption is an important part of the geologic history of the Yucca Mountain region. Yucca Mountain itself is composed of deposits resulting from volcanic eruptions to the north, and several volcanic cones are present in adjacent Crater Flat.

Image from Whitney, J.W., and Keefer, W.R.,eds., 2000, Digital
Data Series 058, CD-Rom.

The USGS provided expert consultation for the PVHA, as well as an aeromagnetic analysis of buried volcanic centers near Yucca Mountain, a study of tectonic controls on basaltic volcanism near Yucca Mountain, and an analysis of a 10-million-year-old basalt dike at the mountain adjacent to the Solitario Canyon fault. The basalt dike represents an analogue for the effects of basalt intrusion into a future waste repository, which has a probability of about 10^-8/year.

Calcite- and silica-filled fractures that were studied as part of the seismic hazards program.
Photo by USGS

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