1. Institute of Earth Sciences (ISTE); University of Lausanne; Lausanne 1015 Switzerland
2. Institute of Earth Surface Dynamics (IDYST); University of Lausanne; Lausanne 1015 Switzerland
3. UCBL, ENSL, CNRS, LGL-TPE; Université de Lyon; Villeurbanne F-69622 France
4. Institut Universitaire de France; 75231 Paris Cedex 05 France