Faults: discrete regions of low viscosity material cutting the upper and lower crust at an angle of 45? are included representing a fault or a planar weakness such as a suture zone.

The coupled fault model produces a strongly asymmetric rift and clearly demonstrates that an initially high angle fault can rotate to become low angle detachment. As the lithosphere extends, rotation of the west dipping high angle fault results in a low angle fault being exposed at the surface which has accommodated substantial movement. After about ~10% extension a secondary, synthetic high angle fault appears dipping east. Both faults continue to rotate with the final rift geometry (50% extension) showing two low angle faults dipping in opposite directions, generated from one initially westward dipping high angle fault. While single seed weaknesses resulted in narrow rift mode, imposing a fault as initial weakness favour a core complex mode.