The velocity structure of the upper mantle of europe from the ambient noise surface wave tomography

Abstract

The method for surface wave tomography based on the records of ambient seismic noise (Ambient Noise Tomography, ANT) is applied to the data from the East European and West European stations. In order to reduce the effects of the earthquakes at long periods, the cross correlation functions were calculated for the time interval of 2001–2003, when distinct clusters of the earthquakes were absent. Using the local dispersion curves in the range of 10–100 s, we reconstructed the vertical velocity sections at the nodes of the 3° × 3° grid. On the basis on these curves, we calculated the horizontal distributions of S-velocity variations in the upper mantle in the depth interval of 75–275 km and the vertical velocity sections along the profiles across the Vrancea zone and the region of the Baltic and Ukrainian shields. The velocity distribution in the Vrancea zone confirms the subduction of the ancient oceanic plate from the east westwards and the detachment of its bottom part, as hypothesized by some authors. Beneath the Baltic Shield lithosphere, there is a low-velocity zone, which can be interpreted as the asthenospheric layer. It is noted that the velocity distributions beneath the Baltic and Ukrainian shields are similar, which probably points to the genetic relationship between these two structures.