Observatoire Multidisciplinaire des Instabilités de Versants




Geodesy

Introduction

The rockslide has been extensively instrumented since 1988 by CETE Lyon, with extensometers, inclinometers, strainmeters, GPS and distancemeters (laser and radar) [Evrard et al 1990; Lemaître et al, 2004]. The displacement rate of the most active zone (Ruins) has increased up to 1.4m/yr in 2008. The other regions have displacements less than 10cm/yr. The map of the network with the displacements is shown in Fig 1. The location of all instruments is available here.
Fig 1: geodetic network

Data and figures

The CETE provides us the displacement data for 7 targets (625,631,635,1002,1003,1010,1100) starting in 1996, and extending until six month before present. The displacement is shown in Figure 2, as well as the precipitation measured at Alpe d'Huez (data from Meteo France). The movement has accelerated on average since 1996, with a strong annual modulation.
The earthquake which produced the strongest shaking during this time preriod is a m=3.5 event which occured at Laffrey, about 5 km away from the rockslide, on January 1st 1999. It did not produce any clear change in the slip rate. But its largest aftershock, a m=2.8 quake which occured in 2005, seems to have triggered an acceleration of the movement (see Fig 2).
Fig 2: Displacement (top), displacement rate (low-passed filtered bellow 10 days) (middle), and monthly precipitation (bottom) measured at Mont-Sec (data from CETE Lyon). The 2 black stars indicates the occurrence of 2 earthquakes which occured at Laffrey, about 5 km away from the rockslide.


Publications et rapports:
  • DURANTHON Jean-Paul (2000) Application de la méthode GPS de localisation par satellite à la surveillance de sites naturels instable, Bull. lab. ponts chaussées (résumé et article complet sur le site du LCPC)
  • Duranthon J-P, L Effendiaz , Memier M, Previtali I (2003), Apport des méthodes topographiques et topométriques au suivi du versant rocheux instable des ruines de Séchilienne, Association francaise de topographie, 94, 31-38. (résumé)
  • Duranthon J-P, L Effendiaz (2004) Le versant instable des "Ruines" de Séchilienne : Point sur l'activité du phénomène et présentation du nouveau dispositif de gestion de la télésurveillance, 252, 29-48 (résumé et article complet sur le site du LCPC)
  • Duranthon, J.-P., F. Lemaitre (2006) "Ground-based radar for the monotoring of the landslide "Ruines de Séchilienne" Geophysical Research Abstracts, Vol. 8, 00720. ( pdf)
  • Evrard, H., Gouin, T., Benoit, A., and Duranthon, J.-P.: Séchilienne, Risques majeurs d'éboulements en masse: Point sur la surveillance du site, Bull. Liaison Lab. Ponts Chauss, 165, 7-16, 1990.
  • Evrard, H., Previtali I. (1993) Séchilienne (Isère) Mont Sec: un versant instable sous haute surveillance, Travaux publics, 1055, 76-79 ( résumé )
  • Helmstetter A., L. Sanchez, S. Garambois, J.-R. Grasso, F. Doré, Y. Orengo, J.-P. Duranthon, P. Pothérat and J. Kasperski, "Seismic monitoring of a huge rockslide (Séchilienne, French Alps)" (Poster) AGU Fall Meeting, San Francisco, Decmber 15-19th 2008
  • Kasperski, J., (2009) "Confrontation des données de terrain et de l'imagerie multi-sources pour la compréhension de la dynamique des mouvements de versants", Thèse de L'Université Claude Bernard Lyon I (pdf)
  • Lemaître, F., J.-P. Duranthon, L. Effendiaz (2004), L'utilisation du radar au sol pour la surveillance des mouvements de terrain, Bulletin des Laboratoires des Ponts et Chaussées, 249, pp 19-34. ( article complet sur le site du LCPC )
  • Pothérat P., Alfonsi P. (2001) Les mouvements de versant de Séchilienne (Isère). Prise en compte de l'héritage structural pour leur simulation numérique, Rev. fr. géotech. 95, 117-131 (résumé)
  • L. Rochet, A. Giraud, P. Antoine and H. Evrard, (1994) The deformation of the Mont-Sec slope in the area of les ruines de Sechilienne, (Isere), Bulletin International Association of Engineering Geology, 50, 75-87.

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