Gravel Hills fault cutting the southwest side of the Black Mountains basalt field, Mojave Desert, California.
Understanding continental deformation and its resultant seismic hazards requires linking of observations over several orders of magnitude of time. This project aims to understand how fault displacements from earthquakes relate to cumulative fault displacement over 100,000s to millions of years. The target of this study is the Mojave Desert sector of the Eastern California Shear Zone, where rapid geodetic rates of strain appear to disagree with long-term fault slip rates.
Primary (red) and secondary (blue) fault of the Pacific - North America plate boundary of California. Mojave Desert region shaded green.
Although active faults of the Mojave Desert are well defined, the slip rates of most of these faults are poorly characterized from syntectonically emplaced offset markers. Existing slip rates are mostly from pre-faulting markers and an assumed onset time of slip, which is inadequate for present needs. The eventual goal of this study is to characterize the long-term geologic slip rates of all right-lateral strike-slip faults in the Mojave Desert. These efforts are presently focussed on the northwest Mojave Desert on the Blackwater fault and Gravel Hills - Harper Lake fault. Preliminary findings indicate slow slip rates of 0.5 mm/yr and < 1 mm/yr on these faults, which is significantly less than slip rates predicted from offset pre-faulting markers and geodetically-constrained block models.
Debris flow levees right-laterally offset 2 meters by the Blackwater fault.
A second aim of this project is to characterize the proportion of strain absorbed by off-fault deformation. This strain includes small faults and distributed simple shear or pure-shear rotation of rocks adjacent to faults. Without some knowledge of this component, the value of well-constrained fault slip rates is not completely known with regard to the total strain absorbed across the plate boundary. The Mojave Province includes one of the better-known examples of off-fault strain adjacent to the Calico fault. Efforts are underway to document off-fault strain between the Gravel Hills and Blackwater faults where a single marker lava flow is cut by both structures.