Numerical Simulations on the Seismic Cycles at the Northeastern Japan Subduction Zone

Abstract:

Numerical simulation is a useful tool to understand the mechanics of an earthquake; however, it is still a great challenge to apply the numerical results to the earth reality. The 2011 Tohoku Mw 9.0 earthquake is a recent large earthquake happened at the northeastern Japan subduction zone, and there are a lots of GPS observations around that area. The coseismic and interseismic GPS observations would put a great constraint on numerical simulations about earthquake cycle. In this study, we set up a 2D model to simulate the seismic cycles at the northeastern Japan subduction zone. The model has 1600 km in width and 340 km in depth. The continent crust is assumed elastic and the mantle lithosphere and asthenosphere are viscoelastic. The geometry of the subducted fault and material properties of the model are chosen based on geophysical observations in that area. The top part of the fault form surface to depth 40 km is assumed controlling by the slip-weakening friction law and is capable of locking or slipping according to the stress changes spontaneously, while the other lower part is supposing to have a constant slip rate of 10 cm/year. This finite-element model is solved with the code PyLith. Numerical results show that at this area, an earthquake of Mw 9 could happen at about every 160 years. The coseismic and interseismic surface deformation of the model agrees well with the GPS observations if we let the model earthquake be the Tohoku earthquake. Another important result is that in order to match the model surface deformation with the observed GPS data, the viscosity of continental lithosphere should be one order of magnitude larger than the underneath asthenosphere.