In Situ Stress in Switzerland – From Pointwise Field Data to a 3D Continuous Quantification

We present a revised and extended database of the orientation of maximum horizontal stress SH and the tectonic regime compiled for Switzerland. The analysis of this compilation reveals that the SH orientation is perpendicular to the topography gradient of the Alps, the Moho and the basement and thus swings from a N-S orientation in the east by 40° counter clockwise to the southwest. The SH orientation shows no statistically significant changes with depth, but at a few individual boreholes the SH orientation changes at various depth significantly indicating local mechanical decoupling. To obtain a spatially continuous description of all stress tensor components for a rock volume in Northern Switzerland we present a semi-generic geomechanical-numerical model. We find that the total stress ratio SH/Sh (with Sh being the minimum horizontal stress) within the Mesozoic cover contrasts significantly between shale units (e.g. Opalinus Clay, 1.2<SH/Sh<1.4) and more competent limestones (e.g. Malm, 1.7<SH/Sh<1.9). The point-wise information of only a few components of the stress tensor is sufficient to estimate the relative local variability of the 3D stress tensor. However, the relia-bility of the absolute stress state has to be tested against stress magnitude data.