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GPS network monitors the Western Alps' deformation over a five-year period: 1993–1998 |
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| Authors: | C Vigny J Chéry T Duquesnoy F Jouanne J Ammann M Anzidei J-P Avouac F Barlier R Bayer P Briole E Calais F Cotton F Duquenne K L Feigl G Ferhat M Flouzat J-F Gamond A Geiger A Harmel M Kasser M Laplanche M Le Pape J Martinod G Ménard B Meyer J-C Ruegg J-M Scheubel O Scotti G Vidal |
| Institution: | Laboratoire de Géologie, Ecole Normale Supérieure – CNRS, 24 rue Lhomond–CNRS, 75231 Paris Cedex 05, France e-mail: vigny@geologie.ens.fr; Tel.: +33-1-44322214; Fax: +33-1-44322200, FR LGTS Univ. de Montpellier - CNRS, bat 22, Pl. E. Bataillon, 34095 Montpellier, France, FR Institut Géographique National, Direction technique, Service de la Recherche, 2 avenue Pasteur, F94165 Saint-Mandé, France, FR Laboratoire de Géodynamique des chaines Alpines, Univ. de Savoie – CNRS Batiment Belledonne, 73376 Le Bourget du Lac Cedex, France, FR Institut de Physique du Globe de Paris, Departement de Sismologie – CNRS, 4 Place Jussieu, 75252 Paris Cedex, France, FR Instituto Nazionale di Geofisica, via di vigna Murata, 605, 00143 Rome, Italy, IT Laboratoire de Geophysique, CEA, BP 12, 91680 Bruyeres-le-Chatel, France, FR Observatoire de la Cote d'Azur, CERGA-GRGS, Avenue Nicolas Copernic, 06130 Grasse, France, FR Geosciences Azur – CNRS, 250 Rue Albert Einstein, 06560 Valbonne, France, FR IPSN–DPRE–SERGD–BBERSSIN, BP 06, 92265 Fontenay-aux-Roses Cedex, France, FR Ecole Superieure des Géometres Topographes Campus universitaire du Maine 1, Boulevard Pythagore, 72000 Le Mans, France, FR CNRS, 14, Avenue Edouard Belin, 31400 Toulouse, France, FR ENSAIS, 24 bvd de la Victoire, 67084 Strasbourg, France, FR LGIT–BP 53, Universite Joseph Fourrier, 38041 Grenoble Cedex 9, France, FR Geodesy and Geodynamics Laboratory, Institute of Geodesy and Photogrammetry, Swiss Federal Institute of Technology, HPV G54 ETH Hoenggerberg, 8093 Zurich, Switzerland, CH Institut Géographique National, SGN, 2 Avenue Pasteur, 94165 Saint-Mandé, France, FR Institut Géographique National, Cité Descartes, 6-8 Avenue Blaise Pascal, 77455 Marne-la-Vallee Cedex 2, France, FR EDF, Direction equipement, CLI, 35–37 rue L. Guerin, BP 1212, 69611 Villeurbanne Cedex, France, FR Laboratoire de Sciences de la Terre Ecole Normale Supérieure de Lyon 46, Allée d'Italie, 69364 Lyon Cedex 07, France, FR |
| Abstract: | The Western Alps are among the best studied collisional belts with both detailed structural mapping and also crustal geophysical investigations such as the ECORS and EGT seismic profile. By contrast, the present-day kinematics of the belt is still largely unknown due to small relative motions and the insufficient accuracy of the triangulation data. As a consequence, several tectonic problems still remain to be solved, such as the amount of N–S convergence in the Occidental Alps, the repartition of the deformation between the Alpine tectonic units, and the relation between deformation and rotation across the Alpine arc. In order to address these problems, the GPS ALPES group, made up of French, Swiss and Italian research organizations, has achieved the first large-scale GPS surveys of the Western Alps. More than 60 sites were surveyed in 1993 and 1998 with a minimum observation of 3 days at each site. GPS data processing has been done by three independent teams using different software. The different solutions have horizontal repeatabilities (N–E) of 4–7 mm in 1993 and 2–3 mm in 1998 and compare at the 3–5-mm level in position and 2-mm/yr level in velocity. A comparison of 1993 and 1998 coordinates shows that residual velocities of the GPS marks are generally smaller than 2 mm/yr, precluding a detailed tectonic interpretation of the differential motions. However, these data seem to suggest that the N–S compression of the Western Alps is quite mild (less than 2 mm/yr) compared to the global convergence between the African and Eurasian plate (6 mm/yr). This implies that the shortening must be accomodated elsewhere by the deformation of the Maghrebids and/or by rotations of Mediterranean microplates. Also, E–W velocity components analysis supports the idea that E–W extension exists, as already suggested by recent structural and seismotectonic data interpretation. Received: 27 November 2000 / Accepted: 17 September 2001 |
| Keywords: | : GPS – ALPES – Tectonics |
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