Localization of inelastic strain with fault maturity and effects on earthquake characteristics

Abstract

Coseismic ruptures release stored elastic strain through a combination of shear displacement along localized, principal faults and distributed bulk inelastic failure of the surrounding material. How inelastic strain localizes as fault systems mature and structurally develop is less well understood owing to the difficulty of measuring the complex, near-field and high-strain regions of coseismic surface ruptures. Here we use radar and optical images to measure the near-field surface displacement field and magnitude of off-fault inelastic strain from 16 historic strike-slip earthquakes that occurred on faults with cumulative displacements and fault slip rates that span almost three orders of magnitude. We show that inelastic shear deformation does localize as fault systems mature: the magnitude of off-fault inelastic strain is largest (34–67%) for fault systems with the lowest cumulative displacements (<3 km) and then rapidly decays to values that saturate around 13–19% for the most ‘mature’ fault systems with cumulative displacements exceeding ~20 km. We find that more localized coseismic ruptures host faster ruptures, generate fewer aftershocks and occur along geometrically simpler fault networks.