An Estimate of Net Extension from a Paleoseismic Transect across US Highway 50, Basin and Range, Nevada

Real time measures of strain accumulation across US Highway 50 are now provided by the recently installed permanent GPS monitoring array of Earthscope. The array straddles a 300-km-wide paleoseismic data gap. We present observations from aerial photography, surficial mapping, fault trenching, tephrochronology, and scarp diffusion analyses to place estimates on the amount and timing of latest Pleistocene displacements along ten rangefront faults distributed across US HWY 50 between latitudes 39 and 40 degrees north. The faults include those bounding the Desatoya, Toiyabe, Monitor, Simpson Park, Toquima, Antelope, Fish Creek, Butte, Egan, and Schell Creek Ranges. The data compliments regional paleoseismic information from previous studies along US Highway 80, the Wasatch Front, Walker Lane, and Central Nevada Seismic Belt. The information is used to estimate a latest Pleistocene net extension rate across the Great Basin and compared to geodetic measurements across the same transect. The results provide an estimate of the amount of strain released by earthquakes across the transect during the latest Pleistocene and show within broad uncertainties that the long-term rate of strain release is similar to short-term strain accumulation. The stability of the displacement field over longer times is supported by the trend of mountain ranges that are roughly perpendicular to crustal velocity vectors. From east to west the ranges become progressively more northeast trending and crustal velocities bend to the northwest. The apparent organization of late Pleistocene ruptures into left stepping strands that trend oblique to rangefronts may reflect Pacific-North American plate relative right lateral motion east of the Central Nevada Seismic Belt.