End of subduction in northern Apennines confirmed by observations of quasi-Love waves from the great 2004 Sumatra-Andaman earthquake

Abstract

Surface waves from the great Sumatra-Andaman earthquakes of 2004 and 2005 that cross Italy south of 44 N display Love-to-Rayleigh scattered waves (quasi- Love phases) diagnostic of sharp lateral gradients in the anisotropic properties of Earth’s upper mantle. Surface waves that traverse Italy further north lack this distinctive phase, documenting a change in the upper mantle fabric that is corroborated by a shift in the fast polarization of shear wave birefringence. These observations suggest that orogen-parallel asthenospheric extension behind the retreating Apennines slab has limited geographical expression. We hypothesize that subduction rollback currently terminates at 44 N, while the upper mantle flow pattern further to the north has been recently rearranged.