GSA Connects 2022 meeting in Denver, Colorado

Paper No. 3-2
Presentation Time: 8:20 AM

BRIDGING EARTHQUAKES AND MOUNTAIN BUILDING IN THE SANTA CRUZ MOUNTAINS, CALIFORNIA (Invited Presentation)


BADEN, Curtis1, SHUSTER, David L.2, FOSDICK, Julie3, BÜRGMANN, Roland1, ARON, Felipe4 and HILLEY, George E.5, (1)Department of Earth and Planetary Science, University of California, Berkeley, 307 McCone Hall, Berkeley, CA 94720, (2)Berkeley Geochronology Center, 2455 Ridge Road, Berkeley, CA 94709; Department of Earth and Planetary Science, University of California, Berkeley, 307 McCone Hall, Berkeley, CA 94720, (3)Earth Sciences, University of Connecticut, Storrs, CT 06269, (4)Research Center for integrated Disaster Risk Management (CIGIDEN) - Ingeniería Estructural y Geotécnica, Pontificia Universidad Católica de Chile, Vicuña Mackenna 4860, Santiago, 7820436, Chile, (5)Department of Geological Sciences, Stanford University, 455 Serra Mall, Building 320, Stanford, CA 94305-2115

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, CA, USA, which reside 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.