Grid decomposition of the SAF rupture model on the nCUBE 2. (top) The model is decomposed into a number of subgrids, here illustrated by the cubes 0-7. The actual model was divided into 512 subgrids, corresponding to the number of processors used in the simulation. (bottom) Illustration of the communication between neighboring subgrids. The 4th-order finite-difference scheme requires a two-point-thick padding layer be added to the outside of each sub-grid in order to propagate the waves correctly. This padding layer always contains the most recently updated wavefield parameters exchanged from the edge of the neighboring subgrid (arrows).