HR: 0830h
AN: G21D-0294    [PDF]
TI: Deformation in the Jura Mountains (France) : First Results of Semi-Permanent GPS Network
AU: * Baize, S
EM: stephane.baize@irsn.fr
AF: IRSN-Seismic Hazard Division, BP 17, Fontenay aux Roses, 92262 France
AU: Walpersdorf, A
AF: Grenoble University-LGIT, Maison des G‚osciences-BP 53, Grenoble, 38041 France
AU: Calais, E
AF: Purdue University-EAS, 550 Stadium Mall Drive, West Lafayette, IN 47907 United States
AU: Tregoning, P
AF: Australian National University, Mills Road, Canberra, ACT 0200 Australia
AB: The western Alps and its foreland have a low to moderate seismotectonic activity, with several damaging historical earthquakes and palaeoearthquakes. The kinematics of the area is characterized by a radial extension in internal Alps and perpendicular compression in the forelands, consistently with a geodynamic model involving a counterclockwise rotation of Adriatic plate as well as the Africa-Eurasia collision. The Jura is the youngest external fold-and-thrust belt related to Alpine orogeny, with evidences of recent (Quaternary faulting) and current (seismicity, geodesy) activity. Previous geodetical studies, using triangulation and GPS data, give very high motions (3-4 mm per y) of Jura relative to stable Europe. Precise knowledge of deformation and slip rates are still unavailable to feed a reasonnable assessment of tectonic activity and seismic hazard. In 2000, we thus started the implementation of a semi-permanent GPS network, consisting in measuring 6 sites during around 10 days, twice a year. The sites were selected in order to represent the six main tectonic blocks separated by suspected active faults. One permanent site is located inside the semi-permanent network. The aim of the semi-permanent network is to enhance the regional permanent GPS network (the REGAL network), in order to infer a local crustal velocity field at lower cost. A first solution of position time series and linear station velocities has been performed using the GAMIT-GLOBK software. 19 REGAL stations and 27 IGS stations have been included in the solution. Formal uncertainties for the velocities in the ITRF 2000 reference frame are of 0.1 mm per y. The RMS of the transformation into ITRF by constraining 5 IGS station velocities to their ITRF 2000 values is 0.5 mm per y. To get a measure of the real velocity precision, several analysis parameters will be tested, like the total time span of REGAL measurements, simulations of semi-permanent measurements at permanent stations or non-linear motion of the sites. The degree of convergence of the velocity results with adding observation epochs for the semi-permanent stations will be evaluated. Our first results indicate that the residual velocities, relative to the stable foreland, are less than 1 mm per y, and they are consistent with the velocity field calculated for the permanent stations in the western Alps (Nocquet and Calais, 2003, GJI), with a relative extension across the western Alps. Moreover, a differential displacement is recorded between the external and the internal Alps, which suggests that the Pennine Frontal Thrust is active, as previously shown by Nocquet and Calais (2003). Most of the semi-permanent points have a residual velocity towards the NW, consistent with the geological models that consider the same propagation of Jura folds and thrusts to the NW. Moreover, the preliminary calculation shows that differential velocities (0.5 mm per y) characterizes the points bordering the Vuache fault, one of the active faults of the Jura, indicating a pure left-lateral strike-slip motion on this fault, in agreement with the seismological and geological data.
DE: 1208 Crustal movements--intraplate (8110)
SC: Geodesy [G]
MN: 2003 Fall Meeting