LATE HOLOCENE SLIP HISTORY RECORDED IN ALLUVIAL FAN SEQUENCES, PANAMINT VALLEY, EASTERN CALIFORNIA

The Panamint Valley Fault Zone (PVFZ) is an active, oblique-slip normal fault that accommodates some of the dextral shear across the Eastern California Shear Zone (ECSZ). The PVFZ is geometrically complex, characterized by a NNW-striking dextral strike-slip fault in the south and a NNE-striking low-angle detachment along the central portion of the fault system. Along the southern fault segment, previous paleoseismic trench studies suggest that 3-4 events occurred during the Late Holocene and that the most recent earthquake (MRE) occurred between 350-500 cal yr B.P. and. Along the central fault segment, radiocarbon dating from displaced alluvial fans suggest that the MRE involved both the low-angle detachment and high-angle strike-slip fault segments. However, the rupture dimensions and magnitude of slip are not well-known. This study investigates offset alluvial fans at ten different sites along the PVFZ to reconstruct the rupture length and fault displacement of the MRE, and to test whether the MRE involved different fault kinematics. Field mapping, measurements of offset geomorphic markers from high-resolution topography, and a calibrated soil chronosequence suggest that the displaced alluvial fans provide constraints on both the MRE and previous surface ruptures. Age estimates from soil chronology suggest at least 3 rupture events are recorded in the Late Holocene fans; these appear to have occurred at ~0.5 ka, ~2 ka, and ~3-4 ka. Displacements of these fans suggest that the MRE is characterized by a minimum surface rupture length of ~35-40 km and dextral-oblique slip of ~2-4 meters. Displacements are progressively greater in older fans; the sum of displacements across an array of normal faults cutting a continuous fan surface suggests a minimum throw of ~14 m since the early Holocene. Restoration of dextral-oblique slip in a latest Pleistocene-early Holocene fan suggests a component of dextral-slip of ~35-38 m and vertical throw of ~7-8 m. These studies imply a relatively fast rate of slip (>3-4 mm/yr) during the Holocene. Collectively, our observations suggest that paleoearthquake ruptures involved both the southern strike-slip segment of the PVFZ and may have involved the detachment along the central fault zone.