Abstract
We study interseismic deformation preceding the Mw8.8 2010 Maule earthquake by means of two-dimensional finite-element modeling. Our goal is to gain insight into the fundamental factors controlling elastic strain build-up and release in subduction zones, and to evaluate different modeling approaches of surface displacement as observed by GPS. We developed a linear elasticity solver that allows us to implement a realistic subducting plate geometry constrained by geophysical data. We test the influence of subducting plate thickness, variations in the updip and downdip limit of a 100% locked interplate zone, elastic parameters, and velocity reduction at the base of the subducted slab. We compared our modeled predictions with interseismic GPS observations along an EW profile crossing the Maule earthquake rupture area, in order to determine best fitting parameters. Our results indicate little influence of the subducting plate thickness at a given downdip limit, which itself has a strong influence on surface deformation. However, the fit to observations is achieved only after reducing the velocity at the base of the subducted slab below the trench region to 10% of the far-field convergence rate. We link this novel result to complementary numerical models that gradually evolve toward considering longer time-scales and complex rheology in order to evaluate the mechanical meaning of the above mentioned inferred kinematic conditions. This allowed us to link the velocity reduction at the base of subducting slabs with a long-term state of high flexural stress resulting from the mechanical interaction of the slab with the underlying mantle. Even a small amount of theses high deviatoric stresses may transfer towards the upper portion of the slab as strain energy that could participate into the mechanical loading of the megathrust and therefore in triggering large earthquakes there.
Highlights
The megathrust interplate shear zone along subduction zones is seen to behave frictionally locked during the time lapse between two large earthquakes
In order to connect geodetic observables at the Earth’s surface and plate coupling along the megathrust fault at depth, different approximations can be used. In this contribution we use 2D numerical models of subduction zones to analyze the influence of different parameters and several plate boundary approximations on kinematic and mechanical conditions accompanying the seismic cycle
First we present our own version of an Elastic Subducting Plate Model (ESPM) as implemented using the finite element method (FEM), with validation against analytical solutions of elastic dislocations
Summary
The megathrust interplate shear zone along subduction zones is seen to behave frictionally locked during the time lapse between two large earthquakes. In this contribution we use 2D numerical models of subduction zones to analyze the influence of different parameters and several plate boundary approximations (including the Back Slip Model, BSM and, Elastic Subducting Plate Model, ESPM) on kinematic and mechanical conditions accompanying the seismic cycle To do this we constrain the deformation caused by different models using interseismic surface velocity vectors measured by GPS previous to the Mw8.8 Maule 2010 earthquake along a trench-normal transect located near the Arauco Peninsula in south-central Chile (Fig. 1). In order to simulate the kinematic conditions of the interseismic phase, we impose a uniform slip along the boundaries of the elastic plate with the asthenospheric mantle (red lines in figure 2), and assume a 100%-coupled seismogenic zone (continuous deformation and stress in between the upper and lower plate from the top surface to the DDL depth). In the simpler geometric setup corresponding to the BSM, a homogeneous slip is imposed along the seismogenic zone (blue line in figure 2) and all other boundaries are fixed
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