A comprehensive and densely sampled map of shear-wave azimuthal anisotropy in the Aegean–Anatolia region

Abstract

A better understanding of what drives surface motion in the rapidly deforming Aegean–Anatolia region requires the comparison of mantle circulation models with reliable and densely spaced seismic anisotropy data. We present a new set of 4279 high-quality splitting data of core-refracted shear waves measured at 216 permanent and temporary broadband seismic stations in Turkey and Greece, and their neighboring countries. When combined with previously published observations, our dataset provides unprecedented dense spatial coverage of the area. The delay time between the fast and slow shear waves is highest in the northern Aegean Sea and northwestern Anatolia (average, 1.5±0.4 s) and lowest in the southern Aegean Sea (average, 0.6±0.4 s). The fast-wave polarization axes are oriented NE–SW over most of Anatolia and the northern Aegean Sea. These show steady counterclockwise rotation of 1° per degree of longitude from eastern Anatolia to the northern Aegean. The only exceptions to this uniform pattern are NNW–SSE to NW–SE orientations in mainland Greece, and NW–SE orientations in the southwestern corner of Anatolia. The overall anisotropy pattern can be explained by instantaneous density–driven mantle flow with additional local effects, such as slab rollback in the Aegean Sea and a slab window beneath southwestern Anatolia.