Constraints on the evolution and vertical coherency of deformation in the Northern Aegean from a comparison of geodetic, geologic and seismologic data

We study the 3-D strain evolution of the northern Aegean and the vertical coherency of deformation. We observe that finite strain orientations in the mantle inferred from published shear-wave (SKS) fast polarization orientations, mid- to upper-crustal stretching lineations in metamorphic core complexes of mainly Miocene age, and the gradient in regional crustal thickness variations, are subparallel to one another. This correlation suggests that the Miocene phase of extension is imprinted in the anisotropic fabric (i.e., lattice preferred orientation, LPO) of the lithospheric mantle, and that the orientation of finite strain due to extension is nearly constant with depth. The lateral variation of published seismic delay times shows a correlation with laterally varying finite strain in the crust inferred from topography and crustal thickness estimates. This correlation suggests that lateral variations in finite crustal and mantle strain are correlated and may point at a pure shear extension mechanism involving the entire lithosphere. We also present a new strain rate model for the northern Aegean based on Global Positioning System (GPS) velocities and additional geological constraints. No-length-change orientations calculated from the model near the North Anatolian Fault (NAF) and North Aegean Trough are not consistent with anisotropy orientations at depth. Present-day extension orientations are systematically, and significantly, more N–S oriented than the stretching lineations and SKS splitting orientations. We conclude that the current shear-dominated surface deformation pattern is not (yet) reflected by significant anisotropy in the lithosphere. Based on some simple calculations, we postulate that the present-day deformation pattern cannot be older than ∼4 Ma, which is consistent with independent arguments on the timing of the propagation of the North Anatolian Fault into the Aegean domain.