EarthScope PLATE BOUNDARY OBSERVATORY REVEALS ACTIVE UPLIFT OF THE SIERRA NEVADA, WESTERN UNITED STATES

The history, rate, and driving forces behind uplift of the Sierra Nevada, western United States, have been the subject of debate. For example, published estimates of the age of the modern elevation based on stratigraphy, paleoseismology, thermochronometry, and isotope paleoaltimetry vary by over one order of magnitude, from less than 3 to greater than 50 million years. Vigorous seismicity and active normal faulting on the east edge of the Sierra Nevada/Great Valley microplate suggest that uplift may be ongoing.

Contemporary vertical motion of the Sierra Nevada bedrock based on GPS measurements from the EarthScope Plate Boundary Observatory (PBO) now have rate uncertainties less than 0.5 mm/yr, and are therefore precise enough to detect rapid uplift. Over one dozen PBO stations (with over 4 years of data) and several longer running stations (with over 10 years of data) on the west slope of the Sierra Nevada move upward at rates between 0.6 and 1.7 mm/yr. This motion is upward with respect to extremely stable reference GPS stations in eastern Nevada, and also with respect to the Earth center of mass, aligned to the origin of the global geodetic reference frame ITRF2005. Additionally, we have analyzed 18 years of ERS and ENVISAT radar data across a profile that spans from the southern Sierra Nevada to Yucca Mountain, Nevada. Interferometric Synthetic Aperture Radar (InSAR) and time series analysis of these data, combined with three-component GPS, corroborate the rates of uplift and show that the eastern edge of the uplift occurs in a narrow zone across the transition between the Sierra Nevada and the Great Basin.

The geodetic uplift rates are similar to slip rates on normal faults along the eastern Sierra Nevada range front (0.2 to 1.2 mm/yr). However, the geodetically imaged uplift is not confined to be near the Sierra Nevada crest or range front faults, and is distributed along the length of the microplate, between latitude 35°–40°, and does not appear to be focused near seismically imaged mantle downwellings. Our results support the hypothesis that the Sierra Nevada is currently undergoing a modern episode of uplift. Measurements indicating the persistence of older elevation can be reconciled with contemporary rates if substantial elevation existed prior to the recent pulse of uplift, and if this pulse initiated more recently than 3 Ma.