Tectonic implications of faulting styles along a rift margin: The boundary between the Rhine Graben and the Vosges Mountains

Seismic reflection data show the effects of the Miocene strike-slip environment on the boundary between the Upper Rhine Graben (URG) and the Vosges Mountains (VM). The border fault zone exhibits three types of responses to the new NW-SE directed regional stress regime. Where it trends N-S, no new deformation is observed. Where it trends NNE-SSW, transpression is evident, and it develops into a few-kilometers-wide zone of intense deformation. Along the NE-SW trending southern boundary of VM, transpression intensifies with an increase in the perpendicular shortening component, and the border fault zone turns into a reverse fault. The uplift of the boundary relative to the graben is estimated to be no less than 1000 m near Colmar, and significantly more along the boundary with the Dannemarie Basin. These estimates, and kinematics considerations, support the hypothesis that the Vosges Mountains are mostly a transpressional feature. The Rhine Fault is mapped and suggested to be a lower Miocene structure that was formed in response to the change in the regional stress regime.