All three siting regions show areas devoid of seismically mappable faults that are bounded by well-defined deformed areas (i.e. seismically mappable faults and folded domains). In NL, the area free of seismically mappable faults is largest.
The tectonic history of Northern Switzerland is influenced by the evolution of the Jura Fold-and-Thrust Belt, the Hegau – Bodensee Graben and the Upper Rhine Graben. The influence on the structural inventory of each tectonic domain decreases with distance from it as demonstrated for instance by the decreasing eastward shortening related to the Jura Fold-and-Thrust Belt.
The basement underlying Northern Switzerland is pre-structured with (i) the Upper Paleozoic Konstanz – Frick Trough (controlled by ENE-WSW-trending faults), (ii) Hercynian faults (NW-SE-trending), and (iii) Rhenish faults (NNE-SSW-trending). The geological past provided numerous evidence that these inherited structures exerted a strong control on the localisation of later tectonic deformation.
Observations made at multiple scales (seismic interpretation, macroscopic and microscopic core description) provide evidence that inherited structures acted as zones of weakness within the less deformed rock volume, localising later strain (i.e. by fault reactivation).
Fracture distribution testifies to the control of mechanical layering: higher fracture frequencies characterise the mechanically competent units (Malm and Muschelkalk Groups), whereas lower fracture frequencies are observed in the less competent units (Opalinus Clay, Lias Group).
In all three siting regions, no evidence for a secondary décollement within the Opalinus Clay was found.
Geodynamically, Northern Switzerland evolved from a first burial to exhumation resulting in terrestrial conditions in the Eocene. The incorporation of Northern Switzerland into the flexural foreland basin of the Alps resulted in a second burial. With the NW-propagation of the Alpine deformation front and the formation of the Jura Fold-and-Thrust Belt, Northern Switzerland evolved towards a wedge-top basin. ZNO, north of the Rafz – Marthalen Flexure (i.e. in the part considered as autochthonous), remained part of the flexural foreland basin. Neogene exhumation resulted in the present-day situation.
Detailed temperature data gained from the analysis of calcite cements provide evidence for locally higher temperatures and thermal gradients than previously estimated for the Mesozoic evolution. Final cooling after burial beneath the Molasse sedimentary rocks is suggested to have occurred essentially after 5 Ma.
