ACTIVE TECTONICS, EROSION RATES, AND TOPOGRAPHIC METRICS IN THE HAYWARD-CALAVERAS FAULT ZONE

In northern California, the geometry of the San Andreas Fault system and how it bends and propagates across the earth’s surface is revealed in the topography through active faulting. Here, active faulting of the Mission and the Arroyo Aguague oblique reverse faults is manifested in the Diablo Mountain Range, where the right lateral Hayward Fault steps left to the Calaveras Fault. The high topography between the 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 restraining bend between the Calaveras and Hayward faults in the Diablo Mountain Range. Millennial denudation rates, measured using ¹⁰Be cosmogenic radionuclide in detrital sand samples, along the Hayward Fault show a steady increase in erosion rates to the northwest, from ~0.04 to ~0.15 mm/yr. Channel steepness index values (k_sn) estimated for southern basins align with erosion rate measurements, with similarly low values ranging from 23 m^0.9 to 51 m^0.9 in the south. These preliminary findings suggest that denudation rates in the restraining bend between the Calaveras and Hayward faults may reflect relatively low tectonic uplift rates in the south and higher tectonic uplift rates to the north, as slip from the Calaveras Fault is transferred northwest to the Hayward Fault. This data provides valuable insights into the partitioning of slip and landscape evolution in regions impacted by active tectonics.