Poroelastic Rebound Following The 2010 M_w8.8 Maule And 2014 M_w8.1 Iquique Earthquakes

Postseismic deformation following megathrust earthquakes is usually modelled by mainly considering two deformation mechanisms,that is,afterslip of the fault and viscoelastic relaxation in the upper mantle.Modelling postseismic deformation without considering the uppermost parts of the crust as a poroelastic medium may produce significant systematic misfits in fitting GPS observations in particular in areas close to the rupture region.In this work we have used three-dimensional models to study poroelastic rebound following the 2010 Mw8.8 Maule and 2014 Mw8.1 Iquique earthquakes that occurred in the central and northern South America subduction zone,respectively.The poroelastic process accounts for the surface deformation due to fluids flow in response to changes in the pore pressure of the rock.We modeled a poroelastic layer to a depth of 16 km and 6 km in the slab and upper plate,respectively,in both regions and compared the results.We used drained Poisson's ratio values of 0.25 in both the slab and upper plate and undrained Poisson's ratio values of 0.31 and 0.34.We further compared the poroelastic effect produced from models with various slab and upper plate thicknesses with the GPS observations(corrected for the effects of afterslip and viscoelastic relaxation)within one,three,and six months following both earthquakes.Our comparisons have revealed the possible poroelastic relaxation time following the Maule and Iquique earthquakes to be three months and one month,respectively.We have also reported the tradeoff between model parameters which includes the thickness of the poroelastic layers and the undrained Poisson;s ratio values for the Maule and Iquique earthquakes.Our study has further revealed that a thick slab and a thin upper plate are required to model the poroelastic rebound following a megathrust earthquake.Tests were also carried out to investigate sensitivity of poroelastic rebound to the Poisson's ratio and shear modulus.We varied the values of these parameters to identify which produced more or less effect on poroelastic deformation.This study has revealed the significant poroelastic deformation that occurred following the Maule and Iquique events and it has also helped constrain the range of the parameters needed to model poroelastic deformation specifically the poroelastic layer thickness.