Modeling Rupture with Heterogeneous Prestress and Through Stable-Sliding Zones, and Implications for an Alaskan-Aleutian Megathrust Earthquake

Motivated by the 2011 M9 Tohoku-Oki event and potential earthquakes on the Alaskan-Aleutian (A-A) Megathrust, we investigate the effects of realistic fault dynamics on slip, free surface deformation, and resulting tsunami formation from an M9 megathrust earthquake. We model four scenarios: a spatially-homogenous prestress and frictional parameter model, two models with rate-strengthening-like friction (e.g., Dieterich, 1992), and one model with spatially-heterogeneous prestress. Firstly, we use the dynamic finite element code FaultMod (Barall, 2008) to show that a simple slip-weakening friction law (e.g., Ida, 1972) can serve as a very accurate proxy for rate-strengthening friction. Secondly, we use the dynamic finite element code EQDyna (Duan and Oglesby, 2006) to model 3-D ruptures, using time-weakening friction as a proxy for rate-strengthening friction, along a portion of the A-A subduction zone. Given geometric, material, and plate-coupling data along the A-A megathrust assembled from the Science Application for Risk Reduction (SAFRR) team (e.g., Bruns et al., 1987; Hayes et al., 2012; Johnson et al., 2004; Santini et al., 2003; Wells at al., 2003), we are able to dynamically model rupture. Adding frictional-strengthening to a region of the fault reduces both average slip and free surface displacement above the strengthening zone, with the magnitude of the reductions depending on the strengthening zone location. The heterogeneous prestress model has the same average slip as the homogeneous model, but with a heterogeneous slip distribution. Corresponding tsunami models, which use a finite difference method to solve linear long-wave equations (Shuto, 1991; Satake, 2002), match sea floor displacement, in time, to the free surface displacement from the rupture models (Tanioka and Satake, 1996). Tsunami models show changes in local peak amplitudes and beaming patterns for each slip distribution. Future work will focus on more realistic fault geometry, stochastic stress distributions, and frictional-strengthening zones that more directly match observations.