Improving geodetic constraints on subduction zone coupling using accurate physics-based models with variable elastic properties

The lack of dense geodetic data near the trench of most subduction zones has made it challenging to accurately infer the pattern of interseismic deformation and, consequently, seismic and tsunami hazard estimates. Most kinematic coupling models ignore the effects of realistic boundary conditions and material properties. Here, we develop a 2D finite element model that incorporates realistic slab thickness and variable shear modulus values to quantify potential biases in these models.

We show that models that do not incorporate a finite slab thickness and variable material properties potentially under-estimate uncertainty about shallow creep rates compared to a more realistic model, while exhibiting a bias toward shallower locking, especially on megathrusts that lack offshore geodetic data. This observation potentially explains a reported gap between the inferred down-dip edge of kinematic locking and the location of episodic tremor and slip in Cascadia. These results highlight the importance of using realistic material properties when estimating the pattern of locking on megathrusts.