The velocity field obtained from targets and GPS can be used to determine the main deformation areas over the 2003.5 - 2006.5 period on the La Clapière site. For that purpose, we proceed by calculating the deformation tensors for each of the cells of a grid covering the landslide area. Thus this is possible to obtain values and directions of the cell extension and shortening, as illustrated on the figure below.
The result shows that the North-West lobes (the landslide upper parts) gather the greater number of deformations. In fact these are unstable and very heterogeneous zones from a kinematics point of view. The specific motion of the wrenching portion, where CPL2 is located, is also highlighted. Finally, the velocity norms that are gradually decreasing while the slope bottom comes closer, result in the appearence of several well-known shortening zones, on both sides of the Iglières Bar.
Vectors representing the extension and shortening (perpendicular) directions and rates calculated from the interpolated 50 meter grid. Scale: the left arrow is 1 μstrain per year (SI). The mesh corresponds to the grid indexes covering the landslide area (the landslide structure can be guessed)
Moreover the study of the velocity field allows to test the validity of simple displacement models. Thus the translation model should be rejected, because the velocity is not constant in every point. As well as the assumption of a rotational motion model could be put forward (see below).
The main simple landslide physical models: translation and rotation (B. Casson et al, 2003)