WHAT DO WE LEARN FROM THE VISCO-ELASTIC RELAXATION FOLLOWING THE 3 LARGEST MEGATHRUST EARTHQUAKES OF THE 21ST CENTURY?

摘要

The beginning of the 21st century has been extremely active, worldwide with the return of giant earthquakes of magnitude close to 9 after a 40-year period of quiescence: Sumatra 2004, Chile 2010, Tohoku 2011. These megathrust earthquakes provide a unique opportunity to observe and quantify visco-elastic relaxation of the different layers in the mantle following the rupture and relate it to rock properties. The change of stress that triggers the deformation is large enough that the deformation is measurable with modern geodetic tools; It is deep enough to probe rheological properties beyond the shallow crust; And above all, and contrary to post-glacial rebound studies that rely on the measure of the tail of the deformation, 20 000 years after the initial impulse, we know the initial displacement and the first response to it from the very beginning.