HIGH RESOLUTION GEODETIC MEASUREMENTS OF CO-SEISMIC FAULT-ZONE DEFORMATION FOR PROBABILISTIC FAULT DISPLACEMENT HAZARD ASSESMENT AND CONFIDENCE INTERVALS ON GEOLOGIC SLIP RATES

Understanding how co-seismic shear strain changes with distance from the primary fault rupture, has importance for characterizing the hazard it poses to critical infrastructure and reliably estimating geologic slip rates from offset geomorphic features. Probabilistic Fault Displacement Hazard Analysis (PFDHA), defines the probability of distributed faulting with distance from the primary fault strand, and has so far been constrained solely from field observations of recent surface ruptures. Here we assess how measurements of near-field surface deformation (< 2 km) of several large magnitude earthquakes (M_w > 7), derived from different geodetic imaging techniques (e.g., optical image and radar amplitude correlation), can be used to better constrain the fall-off of inelastic, co-seismic shear strain away from the primary fault. From the resulting displacement maps we can measure the full across-fault co-seismic surface strain at multiple points along-strike of the surface rupture (n>1500), providing the probability of occurrence of distributed inelastic deformation. Although the field mapping accuracy of expected rupture occurrence dominates the PFDHA hazard, we find geodetic-based measurements can still help reduce the epistemic uncertainty associated with the probability of near-field distributed displacement (< 500 m) for different types of geologic material and macroscopic fault-zone complexity. Assuming fault strain release is an ergodic process, we also discuss how these probabilistic estimates of fault-zone width could characterize the probability a geologic slip rate measurement, taken over some fault perpendicular distance, captures the full, across-fault geologic strain release. High-resolution measurements of near-field deformation from surface ruptures can help reduce the epistemic uncertainty in PFDHA models, providing more precise information to structural engineers, and place confidence limits on geologic slip rates that would be useful input for PSHA.