Structural geology of Central Switzerland - Results of seismic campaign in 2011 in cantons Nid- and Obwalden

GVM (Gas Verbund Mittelland AG) commissioned in 2011 the acquisition of 113 km of 2D reflection seismic as a first step of an integrated exploration campaign for geothermal and hydrocarbon resources in the cantons Nid- and Obwalden (Switzerland]. One of the aims of the seismic campaign was to define the structure of the Helvetic nappes and its base, the internal build-up of the underlying Tertiary sediments and the autochthonous Mesozoic cover. The new data allow defining the internal tectonics of the Drusberg nappe and its base. The deformation style of the Drusberg nappe is characterized by imbrication and ramp anticlines. The base of the Helvetic nappe forms a relatively flat, wide and gently structured synform south of a line Schwendi - Alpnach - Stans. The base of the Helvetic nappes reaches a max. depth of approximately 1.8-2.0 km below the Sarner Aa valley. It is not possible to distinguish between south dipping Molasse and supposed North Helvetic Flysch. The autochthonous Mesozoic cover is less deformed. Few faults and folds may correlate with underlying Permo-Carboniferous troughs. The latter can be identified on the seismic sections by unconformities. (authors)