Mountain rivers reveal the earthquake hazard of geologic faults in Silicon Valley

The 1989, M_w = 6.9 Loma Prieta earthquake resulted in tens of lives lost and cost California almost 3% of its gross domestic product. Despite widespread damage, the earthquake did not clearly rupture the surface, challenging the identification and characterization of these hidden hazards. Here, we show that they can be illuminated by inverting fluvial topography for slip-and moment accrual-rates—fundamental components in earthquake hazard assessments—along relief-generating geologic faults. We applied this technique to thrust faults bounding the mountains along the western side of Silicon Valley in the San Francisco Bay Area, and discovered that these structures may be capable of generating a M_w = 6.9 earthquake every 250–300 years based on moment accrual rates. This method may be deployed broadly to evaluate seismic hazard in developing regions with limited geological and geophysical information.