Dynamic Ridges and Valleys in a Strike‐Slip Environment

Abstract

AbstractStrike‐slip faults have long been known for characteristic near‐fault landforms such as offset rivers and strike‐parallel valleys. In this study, we use a landscape evolution model to investigate the longer‐term, catchment‐wide landscape response to horizontal fault motion. Our results show that strike‐slip faulting induces a persistent state of disequilibrium in the modeled landscapes brought about by river lengthening along the fault alternating with abrupt shortening due to stream capture. The models also predict that, in some cases, ridges oriented perpendicular to the fault migrate laterally in conjunction with fault motion. We find that ridge migration happens when slip rate is slow enough and/or soil creep and river incision are efficient enough that the landscape can respond to the disequilibrium brought about by strike‐slip motion. Regional rock uplift relative to baselevel also plays a role, as topographic relief is required for ridge migration. In models with faster horizontal slip rates, stronger rocks, or less efficient hillslope transport, ridge mobility is limited or arrested despite the continuance of river lengthening and capture. In these cases, prominent steep, fault‐facing facets form along well‐developed fault valleys. Comparison of landscapes adjacent to fast‐slipping (>30 mm/yr) and slower‐slipping (≤1 mm/yr or less) strike‐slip faults in California, USA, reveals features that are consistent with model predictions. Our results highlight a potential suite of geomorphic signatures that can be used as indicators of horizontal crustal motion and geomorphic processes in strike‐slip settings even after river capture has diminished or erased apparent offset along the fault.