Fault interaction at the junction of the Transverse Ranges and Eastern California shear zone: a case study of intersecting faults

摘要

A case study from southern California illustrates the value of detailed geologic data for understanding the kinematics of complex fault systems. The neotectonic behavior of faults at the junction of the Eastern California shear zone (ECSZ) and Transverse Ranges has implications for the interaction of intersecting, segmented fault systems and regional plate boundary evolution. Paleoseismic observations indicate that the North Frontal thrust system (NFTS) has ruptured once in the Holocene with 1.7-m displacement, despite previous speculations of inactivity based on its dissection by younger strike-slip faults. Simple polyphase deformation, in which dextral shear has replaced and overprinted thrusting, is thus not a valid explanation for this system of intersecting faults. This illustrates the limitations of inferring rupture behavior from mapped fault patterns alone. Neotectonic and geomorphic observations along the thrust system also suggest that the thrust segment west of the intersection with the dextral Helendale fault is significantly more active than the segment to the east. This is consistent with a simple block velocity model, in which dextral slip on the Helendale fault is balanced by convergence on the western thrust segment, dextral motion on the poorly studied Pipes Creek fault to the southeast, and inactivity on the eastern thrust segment. This divides the San Bernardino Mountains into domains dominated by thrusting (west) and strike-slip (east), the union of which is a quasistable triple junction. We speculate that this union has migrated to the west as the Mojave Desert has been translated southwards along the San Andreas fault. (C) 2003 Elsevier B.V. All rights reserved. [References: 68]