FIELD MAPPING IN THE 21st CENTURY: RECONSTRUCTION OF FAULT DISPLACEMENT IN ALLUVIAL FAN DEPOSITS, PIUTE CREEK, WHITE MOUNTAIN FAULT ZONE, CALIFORNIA, BASED ON HIGH-RESOLUTION SATELLITE IMAGERY AND FIELD WORK

Fault scarps that develop in alluvial sediments often splay into several near-surface branches. Based on traditional field mapping techniques, the reconstruction of the co-seismic fault displacement is limited and likely underestimates the total displacement. The goal of our study was to quantify the total displacement across several fault scarps that cut the Piute fan, based on a combination of high-resolution remote sensing imagery (60 cm resolution) and ground-based mapping. Previous estimates were also based on offset alluvial deposits, but fewer fault strands had been identified due to limited resolution of the geological and topographic base maps. We produced a new high-resolution tectono-geomorphic map of the Piute alluvial fan, which allowed us to reconstruct the displacement across the fault system.

The Piute Creek fan (2 km²) is located in Owens Valley, along the White Mountains range front north of Bishop. The fan apex is located at the transition to the footwall bedrock, which consists of limestone, sandstone, hornfels, and schist. The western portion of our mapping area is characterized by playa sediments. The fan surface exhibits Quaternary surface levels differentiated by their color and the state of desert-pavement evolution. We further separated the associated deposits by the degree of cementation. Based on this approach we constrained the relative ages of the different surface levels. Furthermore, we observed two sets of fault scarps exposed across the fan: a N-S-trending fault in the south, and a NE-SW-trending fault in the north. These scarps range in height from bearly detectable (c. 20 cm) to 10 m with slope angles ranging from 7 to 25°. We also mapped an up to 25 m high scarp north of the Piute Creek fan. The fan exhibits antithetic normal faults, and synthetic normal faults occur only in the south. Based on measured scarp heights, we approximated a total displacement of ~ 3 m across the northern fan, and ~ 20 m across the southern fan, which is similar to the displacement along a single, 25 m high scarp to the north. Therefore, it is possible to reconstruct the total displacement of a fault even if several scarp branches developed in unconsolidated alluvial sediments. As a next step, we intend to perform laser scanning to reconstruct the 3-D offset precisely across the fan with “cm-scale“ resolution.