Modern Geodynamics of the Southern Baikal Region

摘要

Since the spatial distribution of seismic hazard zones and the time of their reactivation is guided largely by the stress-strain state of the lithosphere and the trend of the impact of tectonic forces, an understanding of the modern geodynamic situation is crucial for the recognition of systematic patterns of seismic processes in a seismoactive region. The tensile stress oriented across the strike of the major morphostructures is pivotal over a considerable segment of the Baikal Rift Zone. The prevalent extensional regime mitigates beyond the rift zone. Shear displacement is the predominant type of faulting in Mongolia. The rather homogeneous stress field is represented by the NE-SW compression, the orientation of which is related to the India-Eurasia convergence. Thus, the stress-strain state of the lithosphere in the southern Baikal region is formed under the influence of two processes: transformation of the anomalous mantle beneath Khangai, Khubsugul, and Baikal, on the one hand, and the India-Eurasia collision, on the other hand. Modern geodynamics at the interaction boundary of these immense natural events is of great interest. Dozer believes that the Tunka district of the southern Baikal region is the most unstable fragment of the southwestern flank of the Baikal Rift. A rapid change in the stress field was recorded in this district in 1979-1981. The detailed study of spatiotemporal variations in the seismic moments of earthquakes in the southern Baikal region carried out in the present work has shown that the regional stress-strain state of the lithosphere is heterogeneous and nonstationary. Analysis of the obtained results makes it possible to explain the main variations recorded in the stress-strain state of the lithosphere in terms of changes in the vertical component S_v of the stress field. This testifies to the strong influence of rifting on modern geodynamic processes in the southern Baikal region. The results obtained make it possible to monitor and model modern geodynamic and seismic processes in the southern Baikal region.