Diffuse deformation explains the magnitude-dependent coseismic shallow slip deficit

Abstract Continental earthquakes produce both localized deformation on faults and diffuse deformation in the surrounding medium. Diffuse deformation can occur up to ~2 km from the faults, and may accommodate a significant part of the surface displacement associated with the earthquake. However, the origin of the diffuse deformation and its role in the rupture process are still not clearly understood. Here, taking advantage of exceptional datasets for the 2019 Ridgecrest, California, earthquake sequence, we perform a joint inversion of InSAR, GNSS, and high-resolution optical correlation data, and demonstrate that the decrease of coseismic slip toward the ground surface observed in earthquake rupture models, also known as shallow slip deficit (SSD), directly correlates with the occurrence of diffuse deformation at the surface. Thus, adding the localized and the diffuse components of the surface deformation, we show that the amount of surface displacement is consistent with the displacement occurring at depth on the faults. Hence, SSD in earthquake source models should generally be interpreted as a proxy for diffuse deformation, a mode of deformation that cannot be accounted for by elastic earthquake models. Revisiting earthquake source models for 29 continental earthquakes, we show that the amplitude of the inferred SSD is inversely proportional to the square of the earthquake magnitude, and that SSD and diffuse deformation are only significant for medium to small magnitude events.