Tomography study of the upper mantle around the TESZ based on PASSEQ experiment data

Abstract

We present a detailed velocity-perturbation model of the Earth's upper mantle in the area around the Trans-European Suture Zone (TESZ) imaged by the teleseismic tomography. The model is based on 12473 P-wave arrival times measured on recordings of 273 stations of the PASsive Seismic Experiment (PASSEQ), which was active during 2006 and 2008. Station and teleseismic event distribution is sufficient to resolve the structure below the PASSEQ array down to a depth of ∼350km. The velocity-perturbation model clearly shows a ∼250-km-thick uniform layer of positive velocity perturbations north-east of the Teisseyre-Tornquist Zone (TTZ) and ∼150-km-thick layer south-west of the TTZ characterized by relatively lower velocity perturbations. The former we associate with the Precambrian mantle lithosphere of the European plate, while the latter represents the much younger Phanerozoic lithosphere. In the uppermost layer of the model (∼40km), the boundary between the two regions closely follows the crustal trace of the TTZ. In deeper layers, the boundary shifts south-westward. At a depth of approximately 120km the region with positive perturbations reaches the northern part of the Bohemian Massif (BM). The shift suggests that the Phanerozoic part of the European plate thrusts over the Precambrian lithosphere. The upper mantle below a depth of ∼250km lacks the pronounced division between the two regions around the TESZ, which allows us to associate these depths with asthenospheric part of the upper mantle.