Based on the data on more than 6,000 arrival times of teleseismic rays recorded at stations of Siberia and Kazakhstan, a 3-D model of lateral inhomogeneities of P─waves velocities was constructed in the upper mantle of southern framing of Siberia, including regions of recent activity of Altai and Sayan and, partly, Baikal Rift Zone. The method which was used to obtain these results is based on the triangulation-block parametrization of the medium and agreement of density of input and output information. The problem of testing the obtained results receives primary attention. Study of method stability has shown that the reconstruction of desired anomalies is satisfactory even in the cases when the noise level in data exceeds a useful signal. Another test was aimed at independently reconstructing velocity structure in two groups of earthquakes. The results of this test demonstrate satisfactory correlation of the obtained patterns. Based on the obtained results, some hypotheses can be proposed concerning mechanisms of development of the region under study. According to the configuration of the obtained inhomogeneities, the activity of the Altai, Sayan, and Baikal regions can be connected with three anomalous regions traced in the upper mantle at depth from 700 to 400 km. Changes in the inhomogeneity character at a less depth is most likely evidence of two-layer convection in the upper mantle. Various rheological models which could reflect the observed fields are considered in the paper.
