2023 Crossroads Abstract
Geodetic data are now being used to estimate fault slip rates in the US National Seismic Hazard Model (NSHM) using kinematic models that relate long-term fault slip rates to surface velocities. However, there are still challenges in inferring fault slip rates using geodetic data, especially in regions of diffuse faulting and distributed off-fault deformation, and best practices for incorporating geodetic data in hazard models are still under consideration. Due to a lack of confidence in off-fault strain rate estimates, the 2014 and 2023 NSHM did not incorporate off-fault rates. Here we implement an alternative approach using geodetically-derived strain rates to infer slip rate deficits directly. We aim to address two challenges of working with strain rates: 1. Strain rate inferences are non-unique, and the uncertainties are poorly understood, and 2. Methods to infer slip deficit rate on faults directly from strain rate are underdeveloped. To address these, we compare strain rate maps and uncertainties in the western US using different methods for estimating strain rates from geodetically-derived velocities. We further implement a viscoelastic earthquake cycle model to run inversions of strain rate observations for slip deficit rates on all western US faults included in the NSHM.