Research.

In complement to seismological records, the knowledge of the ruptured fault geometry and of the co-seismic ground deformation are key data to investigate the mechanics of seismic rupture. This information can be retrieved from sub-pixel correlation of pre- and post-earthquake remotely sensed optical images. However, this technique suffers from a number of limitations, mostly due to uncertainties on the imaging systems and on the platform attitudes, leading to strong distortions and stereoscopic effects.

Here, we propose an automated procedure that overcomes most of these limitations. In particular, we take advantage of the availability of accurate digital elevation models with global coverage (SRTM). This methodology will improve our ability to collect measurements of ground deformation, in particular in the case of large earthquakes occurring in areas with little or no local geophysical infrastructure. Measuring co-seismic deformations from remotely sensed optical images is attractive thanks to the operational status of a number of imaging programs (SPOT, ASTER, Quickbird, USGS-NAPP aerial programs, etc...) and to the broad availability of archived data.

The general procedure consists of generating accurate ground control points (GCP) for each image. An accurate ortho-rectification model is then built, which allows accurate ortho-rectification and co-registration of the set of images. Correlation on the ortho-rectified images then delivers the horizontal ground displacements to analyse.

Technique flow chart