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Beyond the Damage Zone: Characterizing Widespread Inelastic Deformation From Integrated Fracture, Aftershock and Strain Maps of the 2019 Ridgecrest Sequence

Fault damage zones are a key component of the earthquake energy budget and seismic hazard assessment, as they constitute a permanent sink of strain energy, modify the elastic properties of the shallow crust, threaten lifelines, and amplify ground shaking during earthquakes. Measurements of the extent of inelastic zones are typically generated from a single dataset (e.g. fracture or aftershock distribution) and capture an integrated history of deformation spanning multiple earthquakes and aseismic processes. The 2019 Ridgecrest earthquake sequence provides an unprecedented view of the distribution of inelastic deformation from high-resolution imaging, geodetic data, and earthquake catalogs. This rich dataset lets us understand how inelastic strain observed in a single event compares to and contributes to its longer-term cumulative history. We integrate high-resolution maps of fractures derived from post-earthquake lidar and drone imagery, 2D strain maps generated from cross-correlated satellite imagery, and aftershock hypocenters from the Ridgecrest QTM earthquake catalog to characterize the distribution of inelastic deformation around the fault during the coseismic and early postseismic periods. Inelastic deformation extends up to 17 km away from the fault and the decay of fracture density, aftershock density, and geodetic strain with distance from the main rupture is well described by an inverse power law with exponents ranging between 0.8 and 1.1. We compare our measurements of the decay of inelastic deformation to measurements of the extent of the Ridgecrest damage zone from other authors to investigate the relationship between yield strain, shear modulus contrasts, and fracture density, and its implications for the rheology of damage zones. Our analysis shows that discrete inelastic deformation extends kilometers beyond the localized damage zone (<100m) and suggests that distributed, far-field yielding may account for a meaningful part of the fracture energy expenditure of earthquakes, building up over multiple earthquake cycles.

Presenting Author: Alba M. Rodriguez Padilla

Student Presenter: Yes

Day: 4/22/2021

Time: 2:00 PM - 3:15 PM Pacific

Additional Authors