HR: 1330h
AN: S12B-0385    [PDF]
TI: Geophysical Investigation of a Slow Active Thrust Fault: the Trevaresse Fault, France
AU: * Nguyen, F H
EM: fnguyen@ulg.Ac.Be
AF: GEOMAC, University of Liege, Geomac Chemin des Chevreuils 1 Bat B52, Liege, 4000 Belgium
AU: Garambois, S
EM: stephane.garambois@ujf-grenoble.fr
AF: LIRIGM, Joseph Fourier University, LIRIGM Maison des Geosciences 1381 rue de la piscine BP 53 cedex 9, Grenoble, 38041 France
AU: Chardon, D
EM: chardon@cerege.fr
AF: CEREGE-CNRS Aix-Marseille University, CEREGE-CNRS Europole Mediterraneen de l'Arbois BP80 13545 Aix en Provence cedex 04, Aix en Provence, 13545 France
AU: Jongmans, D
EM: Denis.Jongmans@ujf-grenoble.fr
AF: LIRIGM, Joseph Fourier University, LIRIGM Maison des Geosciences 1381 rue de la piscine BP 53 cedex 9, Grenoble, 38041 France
AU: Bellier, O
EM: bellier@cerege.fr
AF: CEREGE-CNRS Aix-Marseille University, CEREGE-CNRS Europole Mediterraneen de l'Arbois BP80 13545 Aix en Provence cedex 04, Aix en Provence, 13545 France
AU: Hermitte, D
EM: hermitte@cerege.fr
AF: CEREGE-CNRS Aix-Marseille University, CEREGE-CNRS Europole Mediterraneen de l'Arbois BP80 13545 Aix en Provence cedex 04, Aix en Provence, 13545 France
AB: As many regions of Western Europe, the Provence area is characterized by slow deformation rates, substantial erosion rates, dense vegetation coverage and human activity. These combined factors affect the detection of geomorphological evidence of slow active faults and consequently the selection of trench sites for paleoseismological studies. However, in terms of seismic hazard, these regions have to be studied carefully. For example, the most important instrumental seismic event in France history, the Lambesc earthquake (M=6), occured in Provence in 1909. A review of recent combined studies (Chardon et al., Bull. Soc. G\'eol. France, t. 174, no. 5, 2003) allows constraining the tectonic and geomorphic evolution of the Tr\'evaresse ridge anticline and associated thrust ramp that obviously ruptured during the 1909 event. In this context, the use of combined geophysical methods can be interesting to determine i) their ability to detect directly, from physico-mechanical contrasts, the location of an active fault (and its characterization) in such a compressional regime where deformation rates are slow, ii) their efficiency in imaging at depth the area around the fault (and consequently, in further constraining geological interpretations), and iii) to observe possible recent displacements in Quaternary deposits. A wide geophysical survey was conducted on four sites along the Tr\'evaresse thrust with multiple methods (radar, electromagnetic, seismic, electrical tomography). Although the fault could not be directly detected from the data, the geophysical survey allowed to unveil the complex structure of the fault zone and, together with geological evidences, provided indications for a southward propagation of the fault system (Nguyen et al., GRA, Vol. 5, 10878, 2003; Chardon et al., GRA, Vol. 5, 08882, 2003). Further geophysical measurements have been made on the site of Ganay, where Quaternary deposits crop out, to investigate this southern branch. Electrical tomographies and the use of forward modelling provide further constraints on the fault system geometry and on the inter-relations between the different geological units. Parallel GPR profiles also show anomalies which could result from the signature of the fault trace, and thus should at least help in locating trenches for paleoseismological studies. \noindent This study is developed with the E.U. S.A.F.E. and the ACI PCN programs.
UR: http://safeproject.free.fr/safe.swf
DE: 7221 Paleoseismology
DE: 7223 Seismic hazard assessment and prediction
DE: 8005 Folds and folding
DE: 8010 Fractures and faults
SC: Seismology [S]
MN: 2003 Fall Meeting