Radial anisotropy along the Tethyan margin

Abstract

SUMMARY We estimate radial anisotropy along the Tethyan margin by jointly fitting regional S and Love waveform trains and fundamental-mode Love-wave group velocities. About 3600 wave trains with S and Love waves and 5700 Love-wave group velocity dispersion curves are jointly inverted for SH-velocity perturbations from a pre-existing, 3-D SV-velocity model. These perturbations are predominantly positive (SH faster than SV) and consistent with PREM, but our model also shows significant lateral variation in radial anisotropy that appears to be correlated with tectonic environment. SH waves travel faster than SV wave beneath backarc basins, oceans and orogenic belts such as the Tyrrhenian and Pannonian basins, the Ionian Sea, the Alps, the Apennines, the Dinarides and the Caucasus. The Algero-Provencal basin, however, is underlain by faster SV velocity. Faster SV velocity of radial anisotropy is also detected within cratons such as the East European platform and the Arabian shield. Beneath hotspots we detect a change in radial anisotropic polarity with depth, which may be caused by transition between the lattice-preferred orientation from horizontal deformation in the asthenosphere and the shape-preferred orientation from vertically oriented melt channels in the lithosphere. We also find significant portion of radial anisotropy within subducting slabs depends on the slab's dip angle.