Upper Mantle Structure Under Western Europe From Fundamental and Higher Mode Surface Waves Using the Nars Array

Abstract

S U M M A R YA generalized inversion of a new data set, consisting of surface wave phase velocities and S, , traveltimes, has resulted in a new shear velocity and density model for the west-European platform (WEPL2). The surface wave phase velocity data set consists of fundamental and higher mode (mode 1-6) measurements from 25 to 70 mHz, using the Network of Autonomously Recording Stations (NARS) array, which was specifically designed for higher mode surface wave measurements. The S, , traveltime data set consists of ISC readings for selected European events. Major features of WEPL2 are a high-velocity lid of 80-140km depth, underlain by a pronounced low-velocity zone between 160 and 220 km depth. The transition zone (400-650 km depth) is characterized by high shear velocities with respect to PREM. The density shows a positive gradient from 60 to 140km depth, followed by an approximately constant value down to 400 km depth. A model for the Baltic shield (SCSH2) is obtained by combination of Nolet's (1977) higher mode phase velocity data set €or western Europe including the Baltic shield and the present phase velocities for the platform. This shield model shows an absence of the low-velocity layer and low shear velocities in the top of the transition layer with respect to WEPL2. Density, although less well resolved, shows lower values for the shield structure between 200 and 350 km depth.

Investigations ofSnandPnphases in the area of the upper Rhine Graben and northern Switzerland

“…The velocities are considerably higher than the ones e.g. Dost (1990) reveals for the European platform.…”

The contrast in upper mantle shear-wave velocity between the east european platform and tectonic Europe obtained with genetic algorithm inversion of rayleigh-wave group dispersion

“…A generalized inversion of surface-wave phase velocities for upper mantle structure in western Europe is presented by Dost (1990). This study targets the structure under a linear network of stations to the west of our path coverage of TE, but it is interesting to note that Dost finds a high-velocity lid at 80-140km depth, while at the same depths we find a lowvelocity zone for TE; Dost finds a deeper low-velocity zone at 160-220km depth.…”

Eurasian surface wave tomography: Group velocities

“…Some of these from last 20 years, segregated coarsely by geographical region, include those in the following lists. In Europe there are the largest number of studies, they include Nolet [1977], Calcagnile and Panza [1978, 1980, 1990 Resolution can be locally better in the regional studies, especially those based on multistation or multievent methods, and global studies are generally more reliable at long periods at and beyond about 150 s for Rayleigh waves and 125 s for Love waves.…”