The stress field in all three siting regions is well defined. This conclusion is based not only on the high density of in-situ borehole tests (MHF, SR), but also on the consistency of observed trends and bandwidths from the stress models.

The prevailing S_Hmax orientation is NNW-SSE, approximately perpendicular to the Jura Fold-and-Thrust Belt, with a small counterclockwise rotation by approximately 10° from the ZNO region to the JO region. Broad consistency of current S_Hmax orientation with Miocene defor­mation features indicates relative stability of the dominant horizontal stress orientation over the past few million years.

Continuity of the orientation of SHmax across Mesozoic sediments (vertically and laterally) derived from boreholes is an indicator of good stress coupling. Significant discrete stress rotations are generally not observed in boreholes in the siting regions.

The stress field is similar in all three siting regions, primarily related to depth and secondarily to mechanical layering, which is coupled to tectonic loading.

The higher stress magnitudes from tectonic loading in more competent layers explains why the stronger formations often exhibit stronger tectonic overprint than the clay-mineral-rich layers (Section 4.3.4). This is amplified closer to the surface (especially in Malm limestones).

The Opalinus Clay exhibits consistent gradients of stress magnitudes, irrespective of the site provenance. Given the differences in tectonic history at the three sites, this finding indicates that the stress field in the Opalinus Clay is relatively insensitive to tectonic loading.

The level of predictability of the stress field beyond the boreholes using 3D geomechanical-numerical models is similar in all three siting regions. Furthermore, the models show that faults do not have any relevant impact on the stress field in the far-field.

The stress regime in all three siting regions can be considered similar. It changes with depth from a thrust faulting stress regime closer to the surface, to a strike-slip and normal faulting stress regimes at greater depth. Where the Opalinus Clay is located at greater depth (in the NL siting region), a stress regime causing normal faulting is dominant, whereas it is normal to strike-slip faulting where at more shallow position (ZNO and especially in JO siting regions).