KINEMATIC DEVELOPMENT OF UPPER PLATE FAULTS ABOVE LOW-ANGLE NORMAL FAULTS IN DEATH VALLEY, CA

The upper plates of detachment faults on the west side of the Black Mountains and on the west side of the Panamint Mountains in Death Valley are extensively faulted. Field observations of diverse intersection geometries between upper plate faults and the detachment, detachment gouge oriented sub-parallel to upper plate structures, and upper plate material incorporated into the detachment gouge confirm a strong kinematic coupling between slip on upper plate faults and slip on the detachment fault. Given this evidence for kinematic coupling between upper plate faults and the detachment fault, a study of the distribution and orientation of upper plate faults reveals information about the shape of the detachment fault and the kinematic history of slip on the detachment.

The projection of upper plate fault data onto a dipline along the detachment permits the analysis of meaningful trends in fault distribution and orientation downdip along the detachment; this projection also allows for a direct comparison between field data and experimentally-derived data. A comparison between the observed distribution of upper plate faults and established patterns generated in analog models of upper plate deformation above a planar detachment suggests that slip along the Black Mountain detachment was not purely orthogonal, and/or the detachment is not planar. Downdip trends in the strike of upper plate faults may reflect a spatial variation in the obliquity of slip along the detachment. The variation in detachment slip direction may be due in part to irregularities along the detachment surface.