Contribution of strata lithology and slope gradient to landslides triggered by Wenchuan Ms 8 earthquake, Sichuan, China

It′s indicated by remote sensing images interpretation and field investigations that within an area of 48678km2, there are more than 48000 landslides geo-hazards triggered by Wenchuan earthquake. The purpose of this study was to detect correlation between landslide occurrences and strata lithology and slope gradient based on Geographic Information System (GIS) by using two parameters: namely landslide-area ration (LAR) and landslide concentration (LC). Within the study area, LAR was defined at 1.4622% and LC was defined at 0.9862 landslides/km2. The result of statistical analyses shows that LAR and LC have a positive correlation with slope gradient and most of the slides occur with slope between 25° and 50°. The Cambrian Formation has the most concentrated landslide activity with highest LAR value of 10%, LC of 6.5 ls/km2, secondly Sinian Formation, Ordovician Formation and intrusive rocks, all of these strata have high susceptibility in terms of earthquake triggered landslide. It is also indicated by comprehensive research of slope, lithology and landslide spatial distribution that in strongly fractured rocks most landslides occur at where the slope angle is less than 30°, in weakly fractured rocks, most landslides occur at where the slope angle is more than 40°.