 The first phase was oblique to the rift axis and led to the formation of en-echelon W-E trending fault sets.The second was orthogonal to the rift axis, leading to overprinting of the early W-E faults by later SW-NE trending faults.The rift system is thought to have formed in response to compression of the lithosphere in front of the zones of collision that formed the Alps and Pyrenees.