Sedimentary signals of recent faulting along an old strand of the San Andreas Fault, USA

Continental transform fault systems are fundamental features in plate tectonics. These complex systems often constitute multiple fault strands with variable spatio-temporal histories. Here, we re-evaluate the complex history of the San Andreas Fault along a restraining bend in southern California (USA). The Mission Creek strand of the San Andreas Fault is a major geologic structure with ~90 km of strike-slip displacement but is currently mapped as inactive. Quaternary deposits record sediment dispersal across the fault from upland catchments and yield key markers of the fault's displacement history. Our sediment provenance analysis from the Deformed Gravels of Whitewater and the Cabezon Fanglomerate provide detrital geochronologic and lithologic signatures of potential sources within the San Bernardino Mountains and Little San Bernardino Mountains. Statistical analysis shows that the Cabezon Fanglomerate is most compatible with the Mission Creek and Morongo Valley Canyon sources, rather than the Whitewater Canyon as previously suggested. We propose that displacement since deposition ~500-100 ka across the Mission Creek strand has separated these deposits from their original sources. These findings challenge the current paradigm that the Mission Creek strand is inactive and suggest that the fault continues to be a primary structure in accommodating deformation along the Pacific-North American plate boundary.

Global catalogue, classification and tectonic origins of restraining- and releasing bends on active and ancient strike-slip fault systems

Restraining- and releasing bends with similar morphology and structure have been described by many previous studies of strike-slip faults in a variety of active and ancient tectonic settings. Despite the documentation of at least 49 restraining and 144 releasing bends along active and ancient strike-slip faults in the continents and oceans, there is no consensus on how these structural features are named and classified, or how their wide range of structures and morphologies are controlled by the distinctive strike-slip tectonic settings in which they form. In this overview, I have compiled published information on the strike-slip tectonic setting, size, basin and bend type, age, and models for active and ancient releasing and restraining bends. Examples of bends on strike-slip faults are compiled and illustrated from five distinctive active strike-slip settings: