Overpressure, vertical stress, compaction and horizontal loading along the North Alpine Thrust Front, SE Germany

Abstract

The North Alpine Thrust Front divides the outer wedge of the northern Alps from its foredeep, the North Alpine Foreland Basin, representing a classic fold-and-thrust-belt system. In its SE German part, this system is characterized by a complex pore pressure distribution, which we investigate to better understand the impact of horizontal loading (tectonic stress) on sediment compaction, vertical stress and overpressure formation. To do so, we analyze velocity, pore pressure and drilling data of 20 deep wellbores along both sides of the North Alpine Thrust Front. Our results indicate that overpressure in the wedge is largely driven syntectonically by horizontal loading, while vertical loading appears to be the main overpressure mechanism not only in the foredeep but also in the footwall of the wedge. Here, pore fluids can support up to 90% or even more of the overburden weight. Still, the lateral transition zone from horizontal to vertical loading conditions likely comprises only a few kilometers. Our study provides real-world evidence of the complex processes of overpressure development in onshore fold-and-thrust-belts and helps to mitigate pore pressure related drilling and exploration risks along the North Alpine Thrust Front in SE Germany.