Tectonic deformation across Northern Switzerland is anticipated to continue at low rates in the future. The future evolution of Northern Switzerland with respect to tectonic loading is expected to be strongly controlled by the protracted effects of the Alpine orogeny, as the Swiss Molasse Basin and the Jura Fold-and-Thrust Belt are part of the North Alpine Foreland and form a mechanical wedge with the interior part of the Alps (Section 4.3).
With respect to the anticipated continued deformation in the siting regions three observations are particularly important:
(i) The past tectonic evolution reactivated inherited faults acting as zones of weakness within the less deformed rock volume (Section 4.3). It should be noted that the retrieved core material drilled within less deformed rock volume contains evidence for strain accumulation also in the rock volume in-between the regional fault zone. The accumulated strain is substantially lower than in the regional fault zones. This is exemplified in the small number of seismically mappable faults (Nagra 2024a, 2024b, 2024c). The phenomenon that inherited faults within the crust guide subsequent strain has been previously reported in literature (e.g. Cooke & Madden 2014, Bürgmann & Dresen 2008, Handy & Brun 2004, Cooke & Murphy 2004, Zoback et al. 2002, Townend & Zoback 2000, Kirby 1985).
(ii) The overall geometry of the regional fault zones inferred from seismic reflection data seems suitable for allowing future slip along the fault plane and thus dissipation of strain. Gently dipping fault segments are more prone to reactivation under thrusting, whereas steeper fault segments will preferentially accommodated strike-slip movements and normal faulting.
(iii) Strain rates inferred from the recent GNSS measurements are low. This implies that the anticipated total strain over the temporal and spatial scale considered for the deep geological repository is limited. Furthermore, the strain rates inferred from GNSS are comparable to strain rates inferred for the main folding and thrusting of the Jura Fold-and-Thrust Belt (Section 4.3.5).
Based on the aforementioned considerations, the most likely tectonic evolution for the next one million years is formulated with ongoing low-rate tectonic loading resulting in homogeneous N‑S shortening and subordinate E-W extension across the siting regions. In addition, ice (un)loading and erosion are likely to predominantly affect the vertical component of the stress tensor and thus potentially impact fault reactivation. The predominant part of the anticipated strain will be dissipated along inherited regional fault zones.
The rock volume in-between the regional fault zones is likely to experience very limited amounts of strain. The evidence for reactivation of inherited faults and the concentration of instrumentally recorded seismicity along such structures provides a strong argument for tectonic stability of the potential disposal zones (Nagra 2024l). Nevertheless, the growth of new faults cannot be entirely excluded, but corresponding fault length and offset will be limited (Nagra 2024i).