Changing Rates and Styles of Crustal Deformation at Timescales of 10 My to 10 Ky

This research addresses the question of whether crustal deformation rates are constant over different timescales. These rates provide a valuable context for the modeling of crustal deformation and assessment of seismic hazards. In particular, we focus on the Sierra Nevada Frontal Fault Zone in the central eastern Sierra Nevada, California, where numerous moraines, outwash surfaces, and deformed strain markers record a truly broad spectrum of deformation rates and styles extending to at least 10 Ma. Our data indicate that both elastic (via fault displacement) and inelastic (via both vertical-axis block rotation and folding) strain can be quantified. The current study centers on Tertiary and Quaternary deformation in three specific study areas: the Sonora Pass, Bridgeport Basin, and Bodie Hills regions. Rates and styles of deformation have been derived from: i) geologic and geomorphic mapping, ii) paleomagnetic sampling of Tertiary volcanic rocks, iii) differential GPS and total-station surveys of faulted landforms, and iv) detailed chronological studies of Quaternary glacial and alluvial deposits using in-situ cosmogenic radionuclide exposure dating techniques. These data enable us to define mean deformation rates, and also, by utilizing markers of different ages, to define changes in deformation rates through time. Of special interest is our ability to document rates of both focused (on-fault) and distributed (off-fault) deformation at multiple timescales, which will enable us to (1) test the constancy of fault slip rates and (2) quantify off-fault strain. These data will be used to test fundamental models of lithospheric deformation and the earthquake cycle.