Active Tectonics, Erosion Rates, and Topographic Metrics in the Hayword-Calaveras Fault Zone
Abstract
In northern California, the complex geometry of the San Andreas Fault system, and how it steps and propagates across the Earth’s surface, is revealed in the topography. Activity along the Mission and Arroyo Aguague oblique reverse faults, located where the right-lateral Hayward Fault steps to the left of the Calaveras Fault, are manifested in the Diablo Mountain Range. The high topography in the restraining step can be observed in lidar imagery and seismicity studies show these faults are connected at depth. In this study, we investigate active tectonics, erosion rates, and topographic metrics from the southern end of the restraining step between the Calaveras and Hayward faults in the Diablo Mountain Range. Millennial denudation rates, measured using 10 Be cosmogenic radionuclide in detrital sand samples along the range front of the Diablo Range, show similar erosion rates across basins, ranging from 0.06 ± 0.005 mm/yr to 0.09 ± 0.008 mm/yr. Downstream samples also show similar rates, ranging from 0.07 ± 0.006 mm/yr to 0.09 ± 0.007 mm/yr. Channel steepness index values (ksn) align with erosion rate measurements, with similarly low values ranging from 23 m0.9 to 51 m0.9. These findings suggest that denudation rates in the southern restraining step between the Calaveras and Hayward faults may reflect relatively low tectonic uplift rates, providing valuable insights into the partitioning of slip and landscape evolution in regions impacted by active tectonics.
