Finite Element modeling of thrust faulting shows that the faults will propagate upward at very low angles from the leading edge of a regional horizontal decollement surface located at various depths in a homogeneous block of crustal material. The angles are consistent with Mode II crack propagation in Linear Elastic Fracture Mechanics and the relationship of stress trajectory and failure in the classic theory of shear fracture. Shallow faults will propagate at a steeper angle than deeper ones. The coefficient of friction does not affect the fault angle, though it probably affects the likelihood of Mode II deformation.