eprintid: 2272 rev_number: 10 eprint_status: archive userid: 6 dir: disk0/00/00/22/72 datestamp: 2020-07-13 07:53:31 lastmod: 2020-07-13 07:53:31 status_changed: 2020-07-13 07:53:31 type: article metadata_visibility: show creators_name: Heuberger, Stefan creators_name: Roth, Philippe creators_name: Zingg, Olivier creators_name: Naef, Henry creators_name: Meier, Beat P. corp_creators: Proseis AG, Schaffhauserstrasse 418, 8050 Zurich, Switzerland corp_creators: Proseis AG, Schaffhauserstrasse 418, 8050 Zurich, Switzerland corp_creators: Geo-Energie-Suisse AG, Reitergasse 11, Zurich, Switzerland corp_creators: Geosfer AG, Teufenerstrasse 3, 9000 St. Gallen, Switzerland corp_creators: Proseis AG, Schaffhauserstrasse 418, 8050 Zurich, Switzerland title: The St. Gallen Fault Zone: a long-lived, multiphase structure in the North Alpine Foreland Basin revealed by 3D seismic data subjects: O subjects: RS2 subjects: SG divisions: S4CE-1 full_text_status: none keywords: Structural geology Reflection seismic data Mesozoic synsedimentary faulting Permo-Carboniferous grabens Neotectonics Induced seismicity Geothermal Power Plant Project St. Gallen abstract: The St. Gallen Fault Zone (SFZ) is a system of major NNE–SSW striking normal faults within the North Alpine Foreland Basin (NAFB), just west of the city of St. Gallen. It used to be only roughly known from 2D seismic data, locally displaying offsets of up to 300 m at the level of the Mesozoic strata. We present a detailed structural interpretation of a recently acquired 3D seismic dataset that reveals the occurrence of multiphase tectonic activity along the SFZ from at least the Late Paleozoic to the early Oligocene, and possibly even later. We can show that the SFZ roots in extensional basement structures that bound small Permo-Carboniferous grabens. Thickness changes in the younger sediments above these Paleozoic grabens indicate several phases of tectonic subsidence during the Triassic and the Jurassic. The Lower Cenozoic units in the northernmost part of the 3D seismic area are also offset by the SFZ. No offsets can be identified in the overlying, shallower part of the Cenozoic units. Most faults constituting the SFZ are favourably oriented in the present-day stress field (SHmax NW-SSE) to be reactivated in strike-slip mode. The seismic events induced by testing operations at the geothermal exploration borehole “St. Gallen GT-1” (SG GT-1) in July 2013 revealed that, even though the seismicity of northeastern Switzerland is considered to be low and diffuse, parts of the SFZ have to be regarded as critically stressed. Combining the interpretation of geological and seismic data, we conclude that the SFZ represents a reactivated basement-rooted normal fault, which was active during several phases in Permo-Carboniferous and Mesozoic times and that is still active today in strikeslip mode. date: 2016 date_type: published publication: Swiss Journal of Geosciences volume: 109 number: 1 publisher: Springer pagerange: 83-102 id_number: doi:10.1007/s00015-016-0208-5 issn: 1661-8726 official_url: https://doi.org/10.1007/s00015-016-0208-5 access_IS-EPOS: limited owner: Publisher citation: Heuberger, Stefan and Roth, Philippe and Zingg, Olivier and Naef, Henry and Meier, Beat P. (2016) The St. Gallen Fault Zone: a long-lived, multiphase structure in the North Alpine Foreland Basin revealed by 3D seismic data. Swiss Journal of Geosciences, 109 (1). pp. 83-102. DOI: https://doi.org/10.1007/s00015-016-0208-5