SCEC2022 Plenary Talk, San Andreas Fault System (SAFS)

A Few Good Bends: Bridging earthquakes and mountain building along the Santa Cruz Mountains Restraining Bend in northern California

Curtis W. Baden, David L. Shuster, Felipe Aron, Julie C. Fosdick, Roland Bürgmann, & George E. Hilley

Oral Presentation

2022 SCEC Annual Meeting, SCEC Contribution #12594
Relative crustal motions along active faults generate earthquakes, and repeated earthquake cycles build mountain ranges over millions of years. However, the long-term summation of elastic, earthquake-related deformation cannot produce the deformation recorded within the rock record. Here, we provide an explanation for this discrepancy by showing that increases in strain facilitated by plastic deformation of Earth’s crust during the earthquake cycle, in conjunction with isostatic deflection and erosion, transform relative fault motions that produce individual earthquakes to geologic deformations. We focus our study on the data-rich Santa Cruz Mountains in northern California, USA, which resid...e along a restraining bend in the plate-bounding San Andreas fault. First, we use a 3D finite element model to predict the accumulation of tectonic deformation surrounding the restraining bend since the range began to uplift at 4 Ma. We then couple this tectonic model with a geomorphic model that predicts how isostatically compensated rock uplift, exhumation, relief, and erosion evolve along the length of the mountain range as strike-slip motion along the San Andreas fault accumulates. We use this coupled model framework to compare predicted and observed quantities for geologically constrained rock uplift, apatite (U-Th)/He thermochronology, topographic relief, 10Be-based erosion rates, and interseismic surface velocities. This approach reconciles these disparate records of mountain-building processes, allowing us to explicitly bridge decadal measures of deformation with that produced by millions of years of plate motion. Our results suggest that deformation accrued over geologic timescales influences the distribution of deformation that develops during and in between earthquakes today. Therefore, careful geologic investigations that record measurements of long-term rock uplift, exhumation, and erosion rates in actively uplifting mountain ranges may be leveraged to further understand distributions of earthquake cycle deformation.