Fig. 2

a Geological map of the Aar Massif (modified after Berger et al. 2016) showing the simplified pattern of major (thickness \(>\,20\,\text {m}\)) and minor (2–20 m) Alpine basement shear zones and associated synclines in the cover units (partly modified from Baumberger 2015; Pfiffner 1978). See Fig. 1a for location of map. HN—Helvetic nappes; bht—basal Helvetic thrust; pf—Pfaffenchopf thrust; wfz—Windgällen-Färnigen zone; tz—Tödi zone; fl—Frisal line; cd—Cavestrau décollement; clz—Clavaniev zone; ugz—Urseren-Garvera zone. We subdivide the study area into four subregions I–IV: I—northern Aar Massif; IIA—Windgällen area; IIB—Färnigen area; IIIA—Tödi area; IIIB—Göscheneralp area; IV—southern Aar Massif. b Summarised stratigraphic column of the eastern Aar Massif (modified after Gautschi et al. 2008; Pfiffner 2015)