[STT54-03] Computing 3-D Viscoelastic Earthquake Cycle Models for Cascadia Using Large-Scale, High-Fidelity Finite Element Methods
Keywords:earthquake cycle, viscoelastic mantle, interseismic coupling
In this study we explore the nature of the critical gap between the ETS and locked zones by identifying the range of locking models in Cascadia which adequately fit available horizontal and vertical geodetic data considering both the effects of viscoelastic mantle relaxation following previous earthquakes and elastic heterogeneity of the lithosphere. We conduct backslip inversions using 3D viscoelastic Greens functions generated with finite element code GAMERA. We assume there is some long-term slip rate given by the relative plate motion that doesn’t contribute to deformation of the overriding plate. All deformation is assumed to come from interface coupling. In the forward model, we impose a saw-tooth backslip history on every patch. Steady backslip is interrupted with sudden co-seismic slip events at regular intervals. The unknown for each patch in the inversion is the backslip rate, which is bounded between zero and the long-term slip rate. The co-seismic slip magnitude on each patch is determined by the backslip rate. To compute earthquake cycles, the viscoelastic Greens functions must be computed out to effectively fully relaxed mantle state (~1500-15000 longest material relaxation times). These calculations are computed using an unstructured low-order implicit finite-element method.