We present a completely revised and extended database of the crustal present-day orientation of the maximum horizontal stress SHmax for northern Switzerland and neighbouring regions. We analysed 32 deep boreholes located in the Molasse Basin of Switzerland from which we interpreted > 30 km of image and caliper logs and picked from these the stress-induced borehole breakouts, drilling induced tensile fractures, and petal centerlines. We also used 105 induced fractures from 139 microhydraulic fracturing tests in 8 boreholes. The interpretation of the data resulted in 64 data records of the SHmax orientation. In addition, we also used an extended and revised dataset of 704 earthquake focal mechanisms computed by the Swiss Seismological Service and derived SHmax orientations from these as well. Combining these data with data records from the World Stress Map database release 2016 resulted in a dataset with 948 data records. The overall regional pattern of the SHmax orientation in the Alpine foreland of Switzerland shows a counterclockwise rotation of approximately 50° from N–S in the northeast to NW–SE in the southwest supporting earlier interpretations that the SHmax orientation is primarily controlled by the gravitational potential energy of the Alpine topography. Beyond this large-scale pattern, no further lateral changes of the SHmax orientation imposed by structural elements or rock property contrasts are resolved due to the resolution limit of the dataset. On average, there is only one reliable data record in Switzerland per 140 km2 with predominant standard deviations of ± 20–25° for individual data records. Thus, small SHmax rotations as well as rotations on lateral scales of a few 10s of km are typically not resolved. We also investigated changes of the SHmax orientation with depth with an emphasis on a potential impact of a mechanical decoupling horizon between the Mesozoic sediments and the underlying basement, which is located in the Middle Muschelkalk (Triassic). For this we used a sub-dataset of 88 SHmax orientations located in northern Switzerland where we have a good coverage of data records in the sediments (n = 43) and in the basement (n = 45). The mean SHmax orientation in the sediments is 166 ± 12° and in the basement 159 ± 22° indicating that a potential decoupling horizon either does not leave an imprint in the SHmax orientation or that decoupling is not acting on a regional scale.

The present-day crustal stress field of the Molasse Basin in Switzerland

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2025年9月16日

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Oliver Heidbach,
John Reinecker,
Tobias Diehl,
Jean Desroches,
Moritz O. Ziegler,
Karsten Reiter,
Tim Vietor,
Silvio B. Giger

摘要

We present a completely revised and extended database of the crustal present-day orientation of the maximum horizontal stress S_Hmax for northern Switzerland and neighbouring regions. We analysed 32 deep boreholes located in the Molasse Basin of Switzerland from which we interpreted > 30 km of image and caliper logs and picked from these the stress-induced borehole breakouts, drilling induced tensile fractures, and petal centerlines. We also used 105 induced fractures from 139 microhydraulic fracturing tests in 8 boreholes. The interpretation of the data resulted in 64 data records of the S_Hmax orientation. In addition, we also used an extended and revised dataset of 704 earthquake focal mechanisms computed by the Swiss Seismological Service and derived S_Hmax orientations from these as well. Combining these data with data records from the World Stress Map database release 2016 resulted in a dataset with 948 data records. The overall regional pattern of the S_Hmax orientation in the Alpine foreland of Switzerland shows a counterclockwise rotation of approximately 50° from N–S in the northeast to NW–SE in the southwest supporting earlier interpretations that the S_Hmax orientation is primarily controlled by the gravitational potential energy of the Alpine topography. Beyond this large-scale pattern, no further lateral changes of the S_Hmax orientation imposed by structural elements or rock property contrasts are resolved due to the resolution limit of the dataset. On average, there is only one reliable data record in Switzerland per 140 km² with predominant standard deviations of ± 20–25° for individual data records. Thus, small S_Hmax rotations as well as rotations on lateral scales of a few 10s of km are typically not resolved. We also investigated changes of the S_Hmax orientation with depth with an emphasis on a potential impact of a mechanical decoupling horizon between the Mesozoic sediments and the underlying basement, which is located in the Middle Muschelkalk (Triassic). For this we used a sub-dataset of 88 S_Hmax orientations located in northern Switzerland where we have a good coverage of data records in the sediments (n = 43) and in the basement (n = 45). The mean S_Hmax orientation in the sediments is 166 ± 12° and in the basement 159 ± 22° indicating that a potential decoupling horizon either does not leave an imprint in the S_Hmax orientation or that decoupling is not acting on a regional scale.