Abstract

The proposed national high-level nuclear waste repository at Yucca Mountain is close to Quaternary cinder cones and faults with Quaternary slip. Volcano eruption and earthquake frequencies are low, with indications of spatial and temporal clustering, making probabilistic assessments difficult. In an effort to identify the most likely intrusion sites, we based a three-dimensional finite-element model on the expectation that faulting and basalt intrusions are sensitive to the magnitude and orientation of the least principal stress in extensional terranes. We found that in the absence of fault slip, variation in overburden pressure caused a stress state that preferentially favored intrusions at Crater Flat. However, when we allowed central Yucca Mountain faults to slip in the model, we found that magmatic clustering was not favored at Crater Flat or in the central Yucca Mountain block. Instead, we calculated that the stress field was most encouraging to intrusions near fault terminations, consistent with the location of the most recent volcanism at Yucca Mountain, the Lathrop Wells cone. We found this linked fault and magmatic system to be mutually reinforcing in the model in that Lathrop Wells feeder dike inflation favored renewed fault slip.

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