NEW HOLOCENE SLIP RATES FROM THE CENTRAL GARLOCK FAULT: IMPLICATIONS FOR THE EASTERN CALIFORNIA SHEAR ZONE AND PACIFIC-NORTH AMERICA PLATE BOUNDARY DEFORMATION

The tectonic significance of the left-lateral Garlock fault in relationship to the eastern California shear zone (ECSZ) and Pacific-North America plate boundary deformation remains a geologic enigma. Geodetic studies imply that the majority of present-day elastic strain accumulation occurs on strike-slip faults oriented northwest-southeast as part of the ECSZ, almost normal to the orientation of the Garlock fault, while strain accumulation parallel to the Garlock fault is minimal. Yet, a large number of offset alluvial landforms along strike of the fault are suggestive of higher tectonic activity than what geodetic strain accumulation rates imply. In an effort to understand the role of this major fault system in accommodating deformation along the Pacific-North America plate boundary, we are analyzing data from four sites on the central section of the Garlock fault. The sites are located within a 21-km stretch of the fault between Trona Road and Randsburg Wash Road in Searles Valley, California. Three of the sites are offset incised channels, whereas the fourth site is an offset alluvial fan. From west to east, the left-lateral offsets at the sites are 49 +/- 8 m (incised channel), 42 +/- 10 m (incised channel), 58 +/- 8 m (offset alluvial fan), and 13 +/- 2 m (offset incised channel), respectively. Two-meter-deep pits were dug in the offset alluvial deposits and samples were collected for Be-10 depth profile and optically stimulated luminescence dating. Given the range in displacements among the four sites our results will prove helpful in understanding whether strain release has been temporarily and spatially constant, and whether the present-day rate of strain accumulation is similar to the geologically determined strain release rates. Ultimately, these results will provide important information on the interaction between the Garlock fault and other faults in the ECSZ, and the role these structures play in accommodating the Pacific-North America plate boundary deformation.