RECONSTRUCTIONS OF LATERAL SLIP ON THE NORTHERN DEATH VALLEY FAULT SUGGEST A LOWER SLIP RATE

Slip rates for strike-slip faults are often derived from correlating offset channels and dating the incised surfaces. However, these slip reconstructions are affected by unknown amounts of uncertainty from geomorphic evolution and the time interval between surface deposition and channel incision. Here, we examine right-lateral slip along the Northern Death Valley fault recorded by three generations of alluvial fans (active to older than >50 kyr) using paired reconstructions of offset channels and fan morphology. We combine field observations, geomorphic mapping, 3-cm-resolution structure-from-motion digital surface models, 1-m-resolution lidar, satellite images, and derived topographic metrics to estimate lateral slip at sites along a ~6 km section of the fault north of Grapevine Canyon and to reexamine the ~65-ka Redwall Canyon alluvial fan ~30 km to the south. We find that the youngest fan surfaces do not preserve evidence of lateral slip while the oldest fan surfaces preserve a suite of small to large offsets. For the middle-age fans, reconstructions of offset channels agree with reconstructions based on fan shape, recording ~9-14 m of dextral slip. For the oldest surfaces, however, reconstructions of offset channels within the fans are incompatible with reconstructions of fan geometry, indicating that the current channel network was entrenched after the fan was abandoned. Reconstructions of fan shape at the Redwall Canyon alluvial fan permit ~115-130 m of offset, less than half that reported previously from channel reconstructions. This result implies a slip rate about half of the previously reported rate since ~65 ka. A reduced 65-ka slip rate on the Northern Death Valley fault is in better agreement with the fault-parallel decadal GPS rates and reconstructions of the younger (middle-age) fans. Slip rates calculated from slip reconstructions of both channels and fans (i.e., at least two paired features) are more robust because they eliminate some uncertainty from unknown geomorphic evolution and timing of channel incision.