Development of a Geodetic-based Probabilistic Fault Displacement Hazard Analysis Using Near-field Geodetic Imaging Data

Abstract:

Understanding how inelastic, co-seismic shear strain attenuates with distance away from the primary fault rupture is important for accurately characterizing the hazard it poses to critical infrastructure and estimating the full geologic slip rate. Probabilistic Fault Displacement Hazard Analysis (PFDHA) is a method that estimates the exceedance probability (or annual rate) of distributed rupture at some distance away from the primary fault. Currently this empirical approach has been constrained by traditional field survey observations of past surface ruptures, but such data are limited due to their relatively large and oftentimes unknown uncertainty, and they are commonly spatially sparse along and across ruptures. Here we present a new geodetic-based PFDHA approach constrained by measurements of near-field surface deformation from several recent large-magnitude (M_w > 7) earthquakes using correlation of optical images. The near-field surface displacement and strain maps allow us to characterize several important properties that affect the attenuation of inelastic strain away from the primary surface rupture, including the effect of rock type, sediment thickness, and degree of fault-zone contraction and extension. From 2D displacement maps of the 2019 Ridgecrest rupture we calculate the finite strain tensor, which shows clear examples of wider zones of inelastic strain along segments that experience extension. Understanding the causes for the variation of fault-zone widths along surface ruptures has importance for reducing the epistemic uncertainty of empirical probabilistic models of distributed rupture, which will in turn provide more precise estimates of the hazard posed by distributed rupture to nearby infrastructure.