We present a 2-D multi-block method for earthquake rupture dynamics in complex geometries using summation-byparts (SBP) high-order finite differences on structured grids coupled to nite volume methods on unstructured meshes. The node-centered nite volume method is used on unstructured triangular meshes to resolve earthquake ruptures propagating along non-planar faults with complex geometrical features. The unstructured meshes discretize the fault geometry only in the vicinity of the faults and have collocated nodes on the fault boundaries. Away from faults, where no complex geometry is present, the seismic waves emanating from the earthquake rupture are resolved using the high-order finite difference method on coarsened structured grids, improving the computational efficiency while maintaining the accuracy of the method.

In order for the SBP high-order nite difference method to communicate with the node-centered finite volume method in a stable manner, interface conditions are imposed using the simultaneous approximation term (SAT) penalty method. In the SAT method the interface conditions and boundary conditions are imposed in a weak manner.

Fault interface conditions (rate-and-state friction) are also imposed in a provably stable manner using the SAT method. Another advantage of the SAT method is the ability to impose multiple boundary conditions at a single boundary node, e.g. at the triple junction of a branching fault.

The accuracy and stability of the numerical implementation are veried using the method of manufactured solutions and against other numerical implementations. To demonstrate the potential of the method, we simulate an earthquake rupture propagating in a nonplanar fault geometry resolved with unstructured meshes in the fault zone and structured grids in the far-eld.