Twenty years of the "Sedrun" landslide : Evolution from analyse of ortho-rectified aerial photographs and comparison with field-work

Category Sedimentology
Group GSI.IR
Location International Geological Congress,oslo 2008
Author Kasperski, Johan۱; Delacourt, Christophe۲; Allemand, Pascal۳; Potherat, Pierre۴
Holding Date 08 September 2008

Based on three stereo pairs of aerial photographs (taken in 1973, 1990 and 2003), three digital elevation model (DEM) have been calculated and used to ortho-rectify three aerial photographs. Then, only qualitative informations can be derived from differential DEMs of different dates. In order to adopt a quantitative approach, we used a method of multi-temporal images correlation which allows to generate displacement maps that can be interpreted in terms of velocity and direction of movements. In order to be validated, these results are compared with classical photogrammetric work made on 52 points in previous studies. Image correlation enables to derived displacement values on numerous points. These measurements show that the average velocity of the landslide have increased from 25cm/yr between 1973 and 1990 to 35 cm/yr between 1990 and 2003. Within the landslide, the velocity fields and their directions show four different zones: their limits have been precisely delimited. The field-work confirms these delimitations of the unstable zones in most cases. Two large open faults in the upper Est part of the Sedrun landslide are not included in the unstable zone by the correlation approach: although they seem to be very active by field investigations because they are impressive, they have not concentrated the unstable activity during the last twenty years.
Muti-temporal images correlation based on ortho-rectified aerial photographs have shown capability to derived displacement maps with numerous points of measure. It enables to give data on the evolution of unstable zones in middle/long term analysis.