Interaction between tectonic and erosion processes on the morphogenesis of an Alpine valley: geological and geophysical investigations in the lower Romanche valley (Belledonne massif, western Alps)

Abstract

International audienceIn the Belledonne massif, the steep Paleozoic Belledonne Middle Fault (BMF) separates micaschists, displaying numerous landslides, from amphibolites. The massif is incised by the lower Romanche river valley. When crossing the BMF, the valley widens into a lozenge-shaped basin recently interpreted as an active pull-apart type structure associated with a major N110 striking Quaternary fault. Multidisciplinary investigations were carried out in the basin to check if this model has implications on the seismic and landslide hazard assessment. This study demonstrated the existence of a N80 sinistral strike slip Séchilienne Fault Zone (SFZ). This fault zone is suspected to offset the BMF by 375 m across the basin. Geophysical experiments revealed that the bedrock depth increases strongly in the basin, up to 350 m. Our study invalidates the active pull-apart origin of the basin and suggests it results from Quaternary glacial and fluvial erosion processes, magnified by the intersection of two inherited structures, the BMF and the SFZ

Paleotopographic control of landslides in lacustrine deposits (Trièves plateau, French western Alps)

“…Recent works (Jongmans et al, 2009) have shown the existence of a strong shear wave (S-wave) velocity contrast (Vs) (N3 on average) between the soft upper layers (clays and moraines; 250 m/s b Vs b 600 m/s) and the substratum made of compact cemented alluvial layers (Vs = 1250 m/s) and Jurassic limestone (Vs = 2000 m/s). With such characteristics, microtremor processing, based on the horizontal to vertical spectral ration technique (H/V technique), has been proven to be one of the most robust and easy exploration tools for mapping the thickness of alluvial or lacustrine sediments (Ibs-von Seht and Wohlenberg, 1999;Delgado et al, 2000;Guéguen et al, 2007;Méric et al, 2007;Le Roux et al, 2010). Measurements were made with a single, three-component, 5-second sensor giving a flat response between 0.2 and 50 Hz and connected to a light seismic acquisition system (Chatelain et al, 2000).…”

1-D and 2-D resonances in an Alpine valley identified from ambient noise measurements and 3-D modelling

“…1b). This incision results from the alternate activity of the Romanche River and the Romanche glacier during the Quaternary glaciations (Montjuvent & Winistorfer 1980; Le Roux et al 2010).…”

“…1b). Recent geological and geophysical investigation (Le Roux et al 2010; Le Roux 2011) has revealed the existence of a N80 sinistral strike‐slip fault zone ( SFZ ), offsetting the BMF by 375 m, and of a significant valley floor overdeepening (from 100 to 370 m depth) across the Séchilienne basin. No sign of recent activity along the SFZ was evidenced by these studies.…”

“…The aim of this paper is thus to better investigate correlation between H/V curve shape and wave propagation by means of experimental and numerical approaches and to derive a strategy for the application of the H/V technique for deep basin investigation. The chosen site is a 5 km long section in the lower Romanche glacial valley (French Alps), which was geophysically and morphologically investigated by Le Roux et al (2010) and Le Roux (2011). The valley exhibits significant variations in width and depth, resulting from lithological changes and fault crossing.…”

Anatomy of landslides along the Dead Sea Transform Fault System in NW Jordan

“…Space borne differential synthetic aperture radar interferometry (DInSAR) has been used for mapping ground deformation phenomena and its relation to mass wasting (Colesanti, 2003). Le Roux et al (2008) have further integrated morphogenetic methods into the study of tectonic and mass wasting processes. The research by Sanchez et al (2010) rests on a cosmoclimatic approach.…”