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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 M w 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. [ABSTRACT FROM AUTHOR]

We investigate seismoelectric (SE) signals accompanying seismic waves radiated from earthquake sources. SE signals are mostly generated from compressional portions of seismic waves by electrokinetic coupling. They contain coseismic electric fields travelling with seismic wave velocity and interface response (IR) waves, which originate at layer interfaces and travel with electromagnetic wave speed. IR wave amplitudes are sensitive to contrasts in poroelastic and electric rock parameters. We introduce SE spectral ratios (SESRs) as a tool to evaluate the influence of IRs on the overall SE signal independently of the earthquake source–time function. Based on data from Northern Chile we show that SESRs show a site specific frequency dependence with a trend of decreasing amplitudes towards increasing frequency. Modelling results reveal that the specific frequency dependence of the SESRs is caused by IRs excited at depths of some hundred metres underneath the recording stations. We analyse the SESR sensitivity towards porosity, permeability, fluid salinity and the depth of the interfaces. We verify that observed SESRs can be reproduced through forward modelling and linearized inversion based on realistic subsurface parameters. [ABSTRACT FROM AUTHOR]