Three-dimensional structure of lateral heterogeneities in P velocities in the upper mantle of the southern margin of Siberia and its preliminary geodynamic interpretation
A three-dimensional model of lateral variations in P wave velocities in the upper mantle of the southern margin of Siberia has been obtained using more than 6000 teleseismic arrival times registered at stations in Siberia and Kazakhstan. The method was based on triangular block parametrization and allows a correlation between output information and the density of input information. The inversion stability has been improved significantly compared to traditional approaches. Special attention was paid to the problem of testing the results obtained. The study of the stability of the method (sensitivity of results toward noise) shows that the reconstruction was stable even if the noise level exceeded the relevant signal. Another test consisted in a reconstruction using two independent sets of events. For these two sets, the velocity structures determined were found to coincide satisfactory. The preliminary interpretation of the results allows us to suggest some mechanisms of development of the study region. According to the tomography images obtained, the upper mantle has a clear convective structure. Two positive velocity anomalies, which are interpreted as descending flows, are well correlated with regions of recent orogeny (Altai and Sayan). Three different structures of flows in the upper manle, which could explain the relief observed and the tomographic images obtained are, considered qualitatively.
