Late Pleistocene regional extension rate derived from earthquake geology of late Quarternary faults across Great Basin, Nevada between 38.5° and 40°N latitude.

摘要

The Great Basin encompasses over two thirds of the Pacific/North American plate boundary and accommodates up to 25 percent of the relative plate motion by active faulting. Although the majority of the deformation within the Great Basin is concentrated along its margins, a small amount of geodetically measured strain is observed between the Central Nevada Seismic Belt and the Wasatch Front. In this area, comparison between short and long-term patterns of strain accumulation and release has been difficult due to slow deformation rates and insufficient paleoseismic data. Thus, in order to document the amount and timing of late Pleistocene displacements geologic studies were performed along ten rangefront faults distributed across US HWY 50. The faults include those bounding the Desatoya, Toiyabe, Monitor, Simpson Park, Toquima, Antelope, Fish Creek, Butte, Egan, and Schell Creek Ranges. The data include geologic maps of Quaternary deposits and fault traces, paleoseismic trenches, scarp diffusion analyses, and soil characteristics in displaced alluvial surfaces. The observations are combined with paleoseismic information from previous studies to estimate a net long-term extension rate and compared to geodetic measurements. The results provide an estimate of the amount of strain released by earthquakes (&sim1 mm/yr) across the interior of the Great Basin during the late Pleistocene and show within broad uncertainties that the long-term rate of strain release is similar to short-term strain accumulation over the same region. The agreement in extension rate estimates over different time scales implies that relatively slow extensional deformation has been operative in the Great Basin east of the Central Nevada Seismic Belt through the late Pleistocene. From east to west the ranges become progressively more northeast trending and crustal velocities bend to the northwest. The organization of late Pleistocene ruptures into left stepping strands that trend oblique to rangefronts and are roughly perpendicular to N60W extension may be the geomorphic expression of a component of right lateral shear within the interior of the Great Basin.