Paper No. 1-1
Presentation Time: 8:50 AM
GEOMORPHIC CONSTRAINTS ON LATE PLEISTOCENE – HOLOCENE SLIP RATES ALONG THE CENTRAL PANAMINT VALLEY FAULT, CA
Despite decades of study, the significance of a mismatch between geodetic velocities and geologic fault slip rates across the eastern California shear zone (ECSZ) remains incompletely understood. Existing estimates of Late Pleistocene – Holocene slip rates along the Panamint Valley fault system (PVFS) are relatively slow (~2-3 mm/yr), but they are limited to a single site along the southernmost fault segment. In contrast, both geologic and geodetic rates suggest that the northernmost segment, the Hunter Mountain fault, may experience slip rates as high as ~5-6 mm/yr. Here, we present preliminary results from an investigation of displaced alluvial fan surfaces along the central PVFS, near Jail Canyon. This site is characterized by a relict channel system associated with a large alluvial fan complex derived from Jail Canyon. The channel is displaced dextrally across a ~500 m wide zone of distributed deformation. Restoration of the channel offsets with the aid of LiDAR suggests 120±10 m of net slip, oriented 300˚, across the PVFS. Without absolute age control, we rely on the degree of soil development and the degree of degradation of the channel risers. We exploit a chronosequence consisting of twelve soils in well-preserved alluvial deposits in Panamint Valley and the Mojave Desert; age control includes OSL, radiocarbon, and cosmogenic 10Be depth profiles. Profile development indices (PDI) of these soils suggest a strong correlation with age; extrapolation of this empirical chronofunction to soils at Jail Canyon implies that the displaced surfaces date 10-27 ka. Modeling the degradation of channel risers is consistent with this age. Calibration of a diffusivity constant against fault scarps and wave-cut shorelines of known age suggests a diffusivity range of 0.8-2.3 m2/ky. Applying this range to the degradation of channel risers at Jail Canyon results in an age range of 10-28 ka. The correspondence of these two independent techniques gives us confidence that the maximum age of the displaced surface is ~28 ka. Thus, our results imply that the minimum slip rate along this segment of the PVFS is ~4.3 mm/yr and could be higher. Our results confirm previous suggestions that the PVFS carries a large fraction of dextral shear in the ECSZ north of the Garlock Fault.