Transient poroelastic response to megathrust earthquakes: a look at the 2015 Mw 8.3 Illapel, Chile, event

Abstract

SUMMARY Large earthquakes can alter regional groundwater pressure, resulting in fluid flow, and the process of restoring hydrostatic equilibrium would in turn lead to observable surface deformation, termed poroelastic rebound, which is one of the most important post-seismic mechanisms for stress transfer and triggering. To constrain the poroelastic contributions to the early post-seismic deformation, we model the hydrologic response within 1.5 months following the 2015 Mw 8.3 Illapel earthquake and remove its effects from the observed geodetic signals. Results demonstrate the post-seismic fluid-flow patterns from the co-seismic high-slip region to the north and south sides, and the northern poroelastic effects are remarkably stronger than those on the south side, verified by northern liquefaction phenomena. Therefore, previous pure afterslip models overestimate the asperities on both flanks of the co-seismic rupture zone and underestimate the middle region, with local errors of more than 50 per cent. It highlights the importance of considering the poroelastic effects, when modelling the transient post-seismic deformation.