HOLOCENE TO RECENT SLIP RATE VARIATIONS ON THE SEVIER DESERT DETACHMENT CONSTRAINED BY GEODESY AND PLUVIAL SHORELINE DEFORMATION

A variety of geodetic and geologic studies within the eastern Basin and Range province indicate that short-term (10¹ – 10⁴ yr) rates of deformation may exceed long-term (>10⁵ yr) rates by a factor of 2–4 on several active fault systems, including the Wasatch fault and the Sevier Desert detachment (SDD). We present new constraints on Holocene to Recent variability of fault slip rates along a transect across the eastern Basin and Range at latitude 39°N, with particular interest in the slip history of the SDD. Modern rates of deformation are constrained by elastic strain accumulation models and velocity data from 17 continuous GPS stations, a four-fold increase over previous studies. These models indicate strain to be subequally partitioned between the SDD (1.7 mm/yr) and faults further to the east, including the Wasatch fault (2.3 mm/yr), and yield a locking depth of ~8 km, consistent with the base of regional seismicity. Holocene rates of deformation on the SDD are constrained by deriving the coseismic displacements necessary to fit observed tectonic deformation of Bonneville and Provo highstand shorelines, measured from recently available high-resolution digital elevation models, and corrected for the effects of isostatic rebound. These displacements are 38.5 m and 33 m for the Bonneville and Provo shorelines, respectively, yielding slip rates on the SDD of 2.2 mm/yr and 2.0 mm/yr for highstand ages of 17.5 and 16.7 ka. These rates are not substantially different from the slip rate on the SDD derived from GPS, but are averaged from the time of the shoreline highstand to the present day. However, differences in coseismic offset between the Bonneville and Provo highstands (5.5 m in 800 yrs) suggest rapid rates of slip on the SDD (~7 mm/yr) between Bonneville and Provo time. Such rapid slip rates may have been driven by crustal unloading during lake-level regression following the Bonneville highstand, as has been proposed for increased Holocene fault slip rates on the Wasatch fault, and underscores the potential for climatic and hydrologic changes to modulate fault slip rates.