Upper mantle structure beneath the Siberian craton and surrounding areas based on regional tomographic inversion of P and PP travel times

摘要

We present a model of 3D seismic anomalies in the upper mantle beneath a part of Northern Asia that includes the Siberian craton, the West Siberian Plate, the mountains framing Siberia (Altai, Sayan and Baikal) and Mongolia. We used the differential travel times of PP and P phases to investigate the deep seismic structure beneath a large part of the Siberian region, where neither stations nor earthquake distributions are sufficient to apply other body-wave tomographic schemes. To show the reliability of the results based on inversion if the PP–P residuals, we performed various tests, including: (1) tests with odd/even data; (2)synthetic tests with checkerboard and realistic patterns; and (3) inversions in other areas with clear structures. Furthermore, for the southern part of the study area, we present another model based on the Inverse Tomographic Scheme (ITS), which uses travel times recorded by worldwide stations from events located in the study area. In the overlapping areas, these two independent models are generally consistent.The main model of this study is obtained by merging the results of the PP–P and ITS schemes. This model shows a clear differentiation between the high-velocity Siberian craton and low-velocity structures beneath the mountains framing Siberia. The area of Cenozoic magmatism in Western Sayan is clearly associated with a low-velocity anomaly. At a depth of 600–700 km, this low-velocity pattern is located beneath the cratonic area, while at shallower depths, it seems to flow around the bottom of the thick craton lithosphere to the SW margin of the craton.