Assessment of earthquake triggering potency for landslides, French Alps : interactions between strong topography contrast, low tectonic loading, and low weathering context.

J-R Grasso (1), L Tatard (1,2), C Voisin (1), C. Sue (3), C. Sira (4)

(1) ISterre, Observatoire et Université Joseph Fourier, Grenoble France
(2) IRD, Lima, Peru
(3) Université de Besancon, France
(4) IBCSF, Université de Strasbourg

Landslides are a major threat to human life and infrastructure in most mountainous and hilly regions of the world. In the last century, Europe has experienced the second highest number of fatalities and the highest economic losses caused by landslides compared to other continents. As a consequence of both the increase in exposure and the possible impact of climate change, the risk associated with landslides is expected to increase. The mechanisms that drive the landslide triggering are numerous. Their couplings result in complex patterns that induced large uncertainties in the prediction of the landslide size and location and occurrence time. Within the context of a low tectonic forcing, we expect, for the French Alps, a M>6 earthquake each 300 years, and 3 M>5 events per century. Since the last glaciation epoch, (104 years ago) an isostasy uplift is the additional forcing on the mountain slopes. Because of the low weathering process, strong topography contrast as eroded by the glaciers still characterized the French Alps geomorphology. In this preliminary work we first analyse case studies of the earthquake-triggered landslides, 1900-2010, French Alps. We evidence a smaller rate of earthquake-triggered landslide for Lambesc, 1909, Mw=6.0, Correncon, 1962, Mw=5.3, and Vallorcine, 2005, Mw= 4.5 earthquakes ; and a larger triggering distance for the Vallorcine, 2005, Mw= 4.5 earthquake than expected from their magnitude as compared to worldwide database. Second we discuss how these patterns can be used to forecast the impact of an ongoing major earthquake in the French Alps and how these patterns may evolve through time within the actual climate change context.