Regional 3-D P-velocity structure of the mantle of northwestern Eurasia; I, Europe, 1
Geyko, V.S.; Tsvetkova, T.A.; Sannikova, N.P.; Livanova, L.P.; Geyko, K.V.
Geofizicheskiy Zhurnal 20(3): 67-91
1998
Document Number: 238781
New large-scale 3-D P-velocity models of the mantle beneath northwestern Eurasia (sectors 20 degrees W-60 degrees E X 30-85 degrees N and 60-80 degrees E X 30-50 degrees N) to 850 km depth and more have been reconstructed. The study area includes Europe and the surrounding water basins, northern coast of Africa, Asia Minor, Near East, Caucasus region, Caspian Sea, Kazakhstan, Middle Asia, northern India, and northwestern China. The initial data have been first-arrival times of P-waves from strong earthquakes and explosions for the 1966-1990 period. To recover the data a new method of seismic tomography proposed by V. Geyko has been used that is based on Taylor approximation of non-linearity of the 3-D inverse kinematic problem. The errors of velocity recovering do not exceed + or - 0.015 km/s. The following fundamental properties of the mantle of Eurasia have been explained. 1) The mantle is subdivided into two shells by the global boundary situated at 550-680 km depth. The upper shell (tectonosphere) is notably inhomogeneous laterally, while the lower one is almost radially-symmetric (deeper than 750-780 km). 2) The age and type of the tectonic structures are reflected in the tectonosphere thickness and its structures. The tectonic structures of the first order (plates) have "roots" piercing the whole tectonosphere, while those of higher order are clear-cut in the upper and unclear in the lower tectonosphere. 3) The intermediate boundary of tectonosphere situated at 390-450 km depth and the asthenosphere are not global. The former is peculiar to the ancient and formed tectonic structures and latter to those actively living now.