Patchwork structure of continental lithosphere captured in 3D body wave images of its anisotropic fabrics

Abstract

This paper presents an overview of research conducted for more than five decades around Vladislav Babuška and collaborators on large-scale seismic anisotropy in tectonically different regions of continental lithosphere in Europe. A wide range of independent data sets and methods are covered. It also briefly touches laboratory measurements of velocity anisotropy on rock samples from the crust and the upper mantle, and emphasizes the importance of considering anisotropy in studies of the Earth structure. The anisotropy is responsible for even larger velocity variations than those due to composition of the most abundant upper mantle rocks (peridotites). The large-scale in-situ measurements of the upper mantle anisotropy capture fabrics of the mantle lithosphere, and enables mapping lateral changes in its structure. The joint inversion/interpretation of the teleseismic body-wave anisotropic parameters, such as variations of directional terms of relative travel time residuals of P waves, shear-wave splitting or the coupled anisotropic-isotropic teleseismic P-wave tomography, image the continental lithosphere as a mosaic of anisotropic domains. Each of the domains has its own thickness and fossil fabric characterized by tilted symmetry axes. We map boundaries of the domains in dependence on the fabric changes. The boundaries can be either narrow and steep or broader and inclined, with an offset relative to boundaries of the related crustal bocks, which can reach several tens of kilometres. This overview presents the European lithosphere-asthenosphere boundary (LAB) and shows examples of anisotropic fabrics of the mantle lithosphere domains and their boundaries in different parts of the European plate.