ASSESSING SURFACE RUPTURE POTENTIAL FOR THE NORTHERN MOJAVE DESERT: IMPLICATIONS OF NEW PATTERNS FOR QUATERNARY FAULTS AND THEIR EVOLUTION

New surficial geologic mapping studies across the northern Mojave Desert identified faults and folds that cut and deform Quaternary materials, providing a systematically developed new data set for evaluating several tectonic problems. Several previously unrecognized faults were identified by tectonic geomorphic features in deformed Quaternary materials. Most of these faults do not show large-magnitude bedrock offset and may represent relatively youthful fault systems. Faults cutting early and middle Quaternary materials form a broad structural network spanning much the northern Mojave Desert. In contrast, faults cutting late Pleistocene deposits (ca. 30-90 ka) are more geographically restricted. The relatively few faults cutting latest Pleistocene to earliest Holocene deposits (ca. 9-15 ka) are restricted to four zones, including the newly identified Paradise and Mesquite Springs faults. This apparent focusing of strain onto relatively few fault zones may represent a change in strain partitioning from a pattern similar to that of the southern Mojave Desert, where numerous faults are active, to one similar to the Basin and Range province, where only three principal faults are active. Patterns of regional deformation apparently have changed appreciably within periods of 100 ka or less. Such rapid changes identified through surficial geologic mapping help pinpoint critical areas requiring focused seismic hazard studies and kinematic analyses. Dynamic models that include reorganization of faults in the northern Mojave Desert are a necessary step for seismic hazard mitigation.