The State of the Art in Studying the Deep Structure of the Earth’s Crust and Upper Mantle beneath the Baikal Rift from Seismological Data

Abstract

Abstract—This review discusses the major milestone results yielded by the regional seismological studies of the deep structure of the Earth’s crust and mantle beneath the Baikal rift since the 1960s to present. It also includes data from recent global models covering a depth interval to below 400 km rarely considered in regional studies. The main focus of the review is laid on the intercomparison of various velocity models of the region, sometimes substantially contradicting each other, which determines the pertinence of this work. In particular, there has been no consensus among different authors as to the crustal thinning beneath the Baikal rift, the thickness of the anomalous mantle layer and the lithosphere. For establishing the causes of the revealed discrepancies, the review briefly compares the inversion methods used in the studies and their resolution. Separate discussion is dedicated to anisotropic properties of the upper-mantle material which is studied from splitting of SKS-waves and from phase and group velocity dispersion data of surface waves. The Conclusions section presents the additional information which can be used for verifying a particular model: there are the results of the studies of thermal, gravitational, geomagnetic, and geoelectric fields and some geological data. The implications of geophysical data covered by the review for the ongoing discussion on the origin of lithospheric extension in the Baikal rift zone are analyzed. It is shown that most of the data (low surface heat flow values and temperatures in the mantle, fairly large bottom depths of the lithospheric magnetic sources, the estimates of the lithospheric thickness from gravimetric and geoelectric data) including purely seismological results (the absence of a general thinning of the crust and lithosphere along the entire rift axis) as well as some geological data contradict the hypotheses of active rifting. However, the existing deep structure models are inconclusive for the ultimate choice between the hypotheses explaining the rift formation by purely passive or mixed mechanisms. The solution of this question requires further, more detailed geophysical study. Thus, the presented review of the deep structure of the Earth’s crust and mantle of the Baikal rift provides the framework for assessing the results of the previous geophysical studies and outlining the prospects of the future research.

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