Three-dimensional velocity model of the crust of the Bohemian Massif and its effects on seismic tomography of the upper mantle

Abstract

We have compiled a representative three-dimensional P-velocity model of the crust of the Bohemian Massif (BM) to provide a basis for removing effects of the crustal structure in teleseismic tomography of the upper mantle. The model is primarily based on recently published 2D velocity models from findings of wide-angle refraction and near-vertical reflection seismic profiles of CELEBRATION 2000, ALP 2002, and SUDETES 2003 experiments. The best fitting 3D model of the BM crust (NearNeighbour model) is complemented by velocities according to the reference Earth model at sites where data are sparse, which precludes creating artificial heterogeneities that are products of interpolation method. To test the model, we have performed tomographic inversions of the P-wave travel times measured during the BOHEMA II experiment and compared the results obtained with and without crustal corrections. The tests showed that the presented crustal model decreases magnitudes of velocity perturbations leaking from the crust to the mantle in the western part of the BM. The tomographic images also indicated a highvelocity anomaly in the lower crust or just beneath the crust in the Brunovistullian unit. Such anomaly is not described by our model of the crust since no seismic profile intersects this part of the unit. The tests also indicated that crustal corrections are of the great importance especially for interpretations of the uppermost mantle down to depths of about 100 km.