Anisotropic features of the Alpine lithosphere in Northern Spain

Abstract

As part of an extensive seismic research carried out in the last years at the Northern part of Iberia affected by the Alpine compressional tectonics, the mantle anisotropic features have been investigated with the shear-wave splitting technique. Two N-S transects across the western Pyrenees and the eastern part of the Cantabrian Mountains were instrumented. In both cases the average fast velocity direction (FVD) and the delay times are remarkably consistent. The δt values are less than 1 s and the average FVD is close to E/W, subparallel to the trend of the Pyrenean belt. However, in each station the results show a significant variation of the splitting parameters with respect to the backazimuthal direction. This azimuthal dependence is compatible with synthetic models including two distinct anisotropic layers and suggests a complex distribution at depth of the anisotropic features, to be related with imprints of different geodynamic processes in the area.