Fig. 1

LIDAR/Swisstopo DTM image of the survey investigation area, to the southeast of the town of Visp, in the Rhone valley at the north end of the Vispa valley (Valais, Switzerland). The thick red line marks a supposed trace of a segment of the Simplon Fault Zone (SFZ, Marthaler 2003), which follows the gorge called the Staldbachgraben, with a ca. E–W trend. The thin red line, trending approximately N–S represents the trace of the Hotée fault, which is probably also associated with the SFZ, as observed by Charles-Louis Joris, a local geologist (personal communication). LIDAR light detection and ranging, DTM digital terrain model. Along segments marked (i), the identification is less clear, whereas along segment (ii) was also mapped as a fault by Marthaler (2003), and a parallel-trending fault can be identified further to the east (green line). Triangles in yellow show the former outcrops, where Joris gathered indications for a neotectonic fault. The localization of the Hotée fault in the tunnel is labeled with a yellow circle. Yellow boxes show locations, where Campani could map the Simplon Line. Orange rectangles show locations, where we performed the ambient vibration measurements, Surveys A, B and C. Yellow patches show landslides and/or sagging areas (Joris, personal communication)