Synthesis of studies for the potential of fault rupture at the proposed surface facilities, Yucca Mountain, Nevada

Abstract

Published data for the Midway Valley area, the proposed site of the surface facilities of a high-level nuclear waste repository at Yucca Mountain, suggest that recognized regional faults have had average slip rates of less than 0.10 mm/yr (0.10 m/1,000 yr) since middle Miocene time. More importantly, the slip rate apparently decreased during the middle to late Miocene and has remained low. Slip rates in the last 8 Ma (Ma = 1,000,000 yr) are estimated to be one-sixth of previous slip rates or less. The decrease in fault activity coincides with the waning of magmatism related to the Painting-brush Tuff, a series of ignimbrite sheets that erupted from the area immediately north of Yucca Mountain. Two important uncertainties are inherent in the slip rate estimates: the relative amount of strike-slip versus dip-slip displacement and the errors in precision of dating offset units.