Structural geology of Central Switzerland : results of seismic campaign in 2011 in cantons Nid- and Obwalden Autor(en): Ebert, Andreas / Genoni, Oliver / Häring, Markus Objekttyp: Article Zeitschrift: Swiss bulletin für angewandte Geologie = Swiss bulletin pour la géologie appliquée = Swiss bulletin per la geologia applicata = Swiss bulletin for applied geology Band (Jahr): 18 (2013) Heft 1 PDF erstellt am: 11.10.2021 Persistenter Link: http://doi.org/10.5169/seals-391139 Nutzungsbedingungen Die ETH-Bibliothek ist Anbieterin der digitalisierten Zeitschriften. Sie besitzt keine Urheberrechte an den Inhalten der Zeitschriften. Die Rechte liegen in der Regel bei den Herausgebern. Die auf der Plattform e-periodica veröffentlichten Dokumente stehen für nicht-kommerzielle Zwecke in Lehre und Forschung sowie für die private Nutzung frei zur Verfügung. 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Vol. 18/1.2013 S.51-59 Structural geology of Central Switzerland - results of seismic campaign in 2011 in cantons Nid- and Obwalden Andreas EbertJ, Oliver Genoni1, Markus Häringi Key words: Helvetics, seismic, Central Switzerland, tectonics, Drusberg nappe Abstract Zusammenfassung GVM (Gas Verbund Mittelland AG) commissioned in Als erster Schritt einer integralen Explorations- 2011 the acguisition of 113 km of 2D reflection seismic kampagne für geothermische Ressourcen und as a first step of an integrated exploration Kohlenwasserstoffe erteilte GVM (Gasverbund campaign for geothermal and hydrocarbon resources in Mittelland AG] 2011 den Auftrag zur Aufnahme von the cantons Nid- and Obwalden (Switzerland]. One 113 km Reflexionsseismik in den Kantonen Nid- of the aims of the seismic campaign was to define und Obwalden (Schweiz). Die Kampagne hatte the structure of the Helvetic nappes and its base, unter anderem zum Ziel, den Aufbau der Helvetischen the internal build-up of the underlying Tertiary Decken, der unterlagernden tertiären sediments and the autochthonous Mesozoic cover. Sedimente (Molasse, Flysch) und der autochthonen The new data allow defining the internal tectonics Einheiten (mesozoische Bedeckung und Grundgebirge) of the Drusberg nappe and its base. The deformation zu bestimmen. style of the Drusberg nappe is characterized by Die neuen Daten bestätigen weitgehend bestehende imbrication and ramp anticlines. The base of the strukturelle Modelle. Der interne Aufbau der Helvetic nappe forms a relatively flat, wide and Drusberg Decke ist gekennzeichnet durch Ver- gently structured synform south of a line Schwendi schuppung und Rampenantiklinalen. Die Basis der - Alpnach - Stans. The base of the Helvetic nappes Helvetischen Decken ist wenig strukturiert und bildet reaches a max. depth of approximately 1.8-2.0 km eine weite und flache Synform südlich einer below the Sarner Aa valley. Linie Schwendi - Alpnach - Stans. Die Basis It is not possible to distinguish between south erreicht an ihrer tiefsten Stelle Tiefen von ca. dipping Molasse and supposed North Helvetic Flysch. 1.8-2.0 km unter dem Sarner Aatal. The autochthonous Mesozoic cover is less In den darunter liegenden tertiären Sedimenten ist deformed. Few faults and folds may correlate with es nicht möglich, einzelne Einheiten zu unterscheiden. underlying Permo-Carboniferous troughs. The latter Die Grenze Molasse - Nord Helvetischer can be identified on the seismic sections by Flysch konnte nicht erkannt werden. In der autochthonen unconformities. mesozoischen Bedeckung können nur wenige Falten und Brüche ausgeschieden werden, welche häufig mit unterlagernden Permokarbon- Vorkommen korrelieren. Das Permokarbon kann auf einigen Linien an Hand von Diskordanzen gut identifiziert werden. Geo Explorers Ltd, Wasserturmplatz 1, AhlO Liestal, [[email protected]] 51 1 Introduction In the cantons Nidwalden and Obwalden Carboniferous. Wells at Wellenberg relating (Central Switzerland), the surface geology is to the surveying of the impermeable Palfris well exposed and allows to construct the Formation by Nagra only reached the base complex nappe and fold structures of the of the Helvetic nappes. The 2,302 m deep Helvetic and Penninic nappes. As a result of geothermal well of Weggis only intersected this, numerous studies were performed in the USM and UMM of the Molasse the past. The first published cross sections sediments. across the Pilatus are given in Kaufmann In the course of the exploration for (1867). A selection of more recent and hydrocarbons in Switzerland during the sixties to important regional studies about the structural eighties several tens of kilometres of seismic geology of the Central Alpine nappes were acquired in Nid- and Obwalden. During are the PhD thesis of Menkveld (1995), the the seventies and early nineties LEAG (AG recent compilation of the Helvetic nappes of für Luzernisches Erdöl), respectively TGK Pfiffner (2011), and the extensive work of (Tiefengaskonsortium) shot 270 km of 2D Hantke (1961). reflection seismic (Fig. 1). While the LEAG However, all the presented information seismic is accessible, the TGK seismic is not about the deeper subsurface rely on available. When the LEAG seismic were extrapolations from the visible geology at the acquired, vibrators were less powerful and surface. Deep wells are missing. The closest were not able to provide the same energy as exploration well that penetrated the nowadays. The data quality is only sufficient Molasse and Mesozoic sediments is Entle- to sketch the autochthonous Mesozoic cover. buch-1 north of the Alpine front (Fig. 1). This It is not possible to define the internal 5,144 m deep well bottomed in the Upper structures and the base of the Helvetic SS .- tu giswi ^ T.ViM bill <A ,.;,,;, |- **r Î1.7M 1171 / m start * I! rrrn i m '' >7M IUI »Ti -" 'StA¦irr allunwil / bi-JL: v: ' 1898 |G :¦ A t nschiesse .: s£l0 a/,, r^i//sv. Sr.h wenrj 'WJ&b ¦.¦¦1%. .v;.: ¦ ¦ i'. lueli fï onborgSBIcB / ^ ¦> ach elii '. IGVM11 .Valo&sTöi ¦ita IVli ?ros^ \ loocri- 'O, nlGVMÏi'-oiTazP n+* % ¦ ¦•- fta îK>6li ,.«•"' i sm ìm^ ; S 1 i Urici:.i.ir.cs ni :,.:i-iinir: lines Fig. : Outline map of the SEAG/LEAG status in Nid- .¦/M TGK exploration ?w ¦ Nagra GVM20I1GVM2011 (CMPs) and Obwalden. Thick black ig.,1 the ^—•-^ :!eep wolls lines represent new of _ seismic lines this study. 77 nappes, the Flysch - Molasse contact, the IPS. Gasser Felstechnik AG made the drilling internal structures of the autochthonous and blasting where source points were not cover and the existence and extend of Per- accessible by vibrotrucks. mo-Carboniferous troughs below the autochthonous Mesozoic cover. Execution Permitting started end of June 2011. Acquisition took place during September 2011. 2 Seismic survey Along seven lines a total length of 112.55 km were acquired (Fig. 1). Additionally, two Motivation for a new survey pseudo lines were recorded (GVM 11-01/02 Currently, Switzerland depends 100% on and 11-04/07) by simultaneous recording imports in case of gas. Only one well, the along both parallel lines GVM 11-01 and 11- Entlebuch-1 well, produced a small gas 02, respectively GVM 11-04 and 11-07. while volume of around 74 Mio. m3 within the years shooting took place along one line. Despite 1984-1994. Comparing to neighboring countries the difficult topography and owing to the the exploration status in Switzerland is good and dense road network in Nid- and low. Most of the underground data from seismic Obwalden, even in the wooded mountain observations or drilling are old and in areas, it was possible to achieve fairly many locations of dissatisfying quality. straight lines. 97% of shot points were Several indications for potential gas sourced by vibrotrucks. accumulations in the subsurface make the area of The deployed vibrators of type HEMI Mertz the Central Alps attractive for an M 12 achieve a peak force of 47,700 lbf. Operation exploration. Such indications are e. g. the gas finding took place with four trucks wherever in the well Entlebuch-1 (Lahusen & Wyss possible. However due to limited space 1995), numerous gas seeps from Lungern to and/or environmental conditions vibrator Alpnach (e. g. Greber et al. 1995), gas blowouts count had occasionally to be reduced. For in the wells EWS Wilen (Wyss 2001) and blasting 2-2.5 kg of explosives (supergel 30) Wellenberg SB1 (e. g. Nagra 1997). were used in drill holes up to 15 m deep. The Based on these conditions, seismic surveys distance between the source points was were acquired in the past in Nid- and 50 m and 25 m between the receiver points. Obwalden. However, as described above, Hydrophones were used from Stansstad to the data quality is insufficient to describe Hergiswil across the «Vierwaldstättersee» the subsurface in detail.