Block rotation and termination of the Hosgri strike-slip fault, California, from three-dimensional map restoration

Abstract

The Hosgri fault is located immediately offshore of south-central California and is part of the transform boundary between the Pacific and North American plates. This fault terminates to the southeast into east-trending folds and reverse-separation faults of the western Transverse Ranges. Our new structure-contour maps of deformed horizons show a spatial relationship between faulting and folding consistent with right-lateral slip. Restoration of these digital maps quantifies post-Miocene right-lateral slip across the southern Hosgri fault to be 3.5 km. This slip is absorbed by folding, thrust overlap, and clockwise vertical-axis rotation of elongate blocks between strands of the fault. The restored part of a block located to the east has rotated 8° clockwise. Extrapolating this restored rotation to the 50 km block length produces an estimate of 7 km of dextral shear for a total, including the 3.5 km fault slip, of 10.5 km of post-Miocene displacement. Our three-dimensional approach precludes interpretations for reverse slip on the Hosgri fault, and is not consistent with models for more than 80 km of late Cenozoic right-lateral fault slip.