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

Coseismic ruptures release stored elastic strain by 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 due 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 spanning almost three orders of magnitude in cumulative displacement and fault slip rates. Our results show that inelastic shear deformation does localize as fault systems mature, where the magnitude of off-fault inelastic strain is largest (34-67%) for fault systems with the lowest cumulative displacement (< 3 km) that then rapidly decays to values that saturate around 13-19% for the most ‘mature’ fault systems with cumulative displacement exceeding ~20 km. We find that more localized coseismic ruptures host faster ruptures, generate fewer aftershocks and occur along geometrically simpler fault networks.