Connecting the Seismic Cycle to the Long-Term Topographic Evolution at Convergent Margins

Subduction zones produce the largest earthquakes. However, our understanding of the connections between earthquakes' spatial-temporal occurrence and long-term tectonic deformation at convergent margin is limited. Subduction zone earthquake cycles is usually interpreted in three stages: Interseismic - superposition of steady elastic strain accumulation and occasional short duration aseismic strain release, Coseismic - rapid opposite-direction release of accumulated elastic strain, and Postseismic - superposition of afterslips and viscoelastic flow in mantle wedge and lower crust. However, the way strain accumulates interseismically which may be related to the generation of long-term deformation and uplift in the forearc region is still a matter of debate. Moreover, when integrated over time, coseismic uplift poorly matches the longer-term vertical deformation in most convergent margins. To better understand these relationships, we investigate numerically how coseismic slip and long-term deformation accumulate and interact at subduction zones by using a robust, adaptive, multi-dimensional, finite element method solver, Dynearthsol3D, on a 2D continuum visco-elasto-plastic (VEP) model. To simulate stick-slip instabilities and subsequent healing, we integrated a strongly rate and state dependent friction coefficient into this VEP model with a dynamic time stepping technique. We set the conditions in this model to a realistic convergent margin setting that resembles Sumatra region. Our results show that we can simulate tectonic dynamics (long-term deformation) problem while not losing resolution during seismic (short-term deformation) events. Moreover, we also find out that earthquake occurrence, magnitude, and fault slip behaviors (locking, stick-slip, or creeping) are highly dependent on parameters like static friction coefficient and pore fluid pressure. By introducing bathymetric features on subducting interface, our approach can also explore mechanisms that could explain how strain accumulation in space and time is modified by the presence of large asperities at the subducting interface.