Fig. 7

Seismic cross-section across St. Gallen Fault Zone (SFZ), Unterlören Graben and Roggwil Fault Zone (RFZ) in the northern part of the area covered by 3D seismic data. See Fig. 4 for location of section trace. The Unterlören Graben is bounded by the SFZ in the WNW and the RFZ in the ESE. High-amplitude PC reflections in the basement help localising the downward continuation of the graben bounding faults. PC reflections seem to also occur up to c. 1.5 km eastward of this graben. The potential upward continuations of the SFZ and RFZ above the reflections at the level of the Mesozoic strata do not reach higher than 2.6–2.8 km below terrain (i.e. 700–800 m above TMa). No direct structural link can be made between the SFZ faults and the three faults mapped at the surface (see also map view in Fig. 4). This is either because there is no such link, or because it cannot be seen due to the laterally discontinuous nature of the Molasse deposits making fault interpretations in the Molasse units a very challenging task. In addition, this section is located at the very northern edge of the 3D seismic where seismic coverage is deficient. Further to the south, reflection offsets along the SFZ in the lowest Molasse units do not reach higher than c. 450–650 m above TMa. The blue tick mark indicates the location of the intersecting section shown in Fig. 11