At ocean-continent subduction interfaces, there is a fundamental partitioning between the mechanisms leading to elastic strain accumulation and release during megathrust earthquakes, and processes that lead to deformation of the upper plate generating topographic relief. For example, in the case of the Andean subduction, how those two processes interact is unknown and no current geodynamic model appears to explain satisfactorily both, the generation of the large earthquakes and the topographic relief of the Andes-Altiplano, as end products of the subduction process. We address this problem by focusing onto a few examples, amongst these:
– The Andes in the framework of LIA Montessus de Ballore, of the Labex UnivEarthS, de l'ANR "Mega-Chile".
– The Caribbean subduction where megathrust rupture potential is unknown, and active deformation of the upper plate needs further study.
– The Hellenic subduction and the Aegean, where the irruption of the North Anatolian Fault a few million years ago appears to have accelerated dramatically rates of plate convergence across the subduction interface (European project Marie-Curie ALERT).
Intracontinental megathrusts at the front of collisional mountain belts, associated with
deep subduction processes, are in the same category of problem as the foregoing. For these thrust systems we address the problem of short-term mechanical coupling and segmentation,
both responsible for the location and size of large earthquake rupture. The past seismic ruptures are studied in the field using geomorphology and paleo-seismology. The link
between mechanical coupling and the long-term evolution of the thrust system and underplating
processes will be further studied in the perspective of recent pioneer work.
As tectonic processes of topographic build-up on subduction and thrust margins interact with surface processes (erosion, incision, sedimentation), we attempt to decipher the tectonic versus climatic forcing contributions by an approach based on precise observations of landscape evolution.