Abstract
Methods of separation of gravity anomalies related to mantle density inhomogeneity are developed. Based on the inversion of these anomalies with regard to some constraints obtained from seismic data, the map of lithospheric thickness beneath the Baikal rift zone and adjacent regions was made. The lithospheric thickness beneath the Baikal rift zone is estimated to be 40–50 km, i.e. the lithosphere is thinned here to a crustal thickness. Beneath the Siberian platform the lithospheric thickness increases to 200 km, and underneath the Trans-Baikal region of moderate Cenozoic tectonic activity it ranges from 75 to 160–175 km. Therefore, a wide asthenospheric upwelling was revealed beneath the rift zone. The data available on the configuration of the Baikal depression and that of the crust and the lithosphere as a whole made it possible to estimate the magnitudes of extension at different lithospheric levels. The significant increase in extension with depth implies that rifting in the Baikal zone was caused by asthenospheric diapirism.
Highlights
Problems of determining locations of earthquakes in space and time and earthquake forecasting are among top priorities in the modern studies of seismicity
(2) In the western regions, the block structures resulting from the crust destruction, which are mainly represented by lense-shaped forms elongated in the submeridional direction, tend to dominate
For the purpose of analysis of relationships between the seismic process and faults, it is reasonable to consider that a fault is active in the recent geodynamic stage if earthquake foci were registered in the zone of its dynamic influence [Sherman et al, 1983] within the past 100 years
Summary
Problems of determining locations of earthquakes in space and time and earthquake forecasting are among top priorities in the modern studies of seismicity. It is noteworthy that the submeridional boundary identified by variations of the crust thickness is reflected in the fault-block structure of Central Asia as shown the atlas of the territory of China and neighbouring countries in [Ma Xingyuan et al, 1987] and in the map in [Ma Xingyuan, 1990]. It reflects a 100-km difference between depths of the lithosphere in the eastern and western areas (~180 km and ~280 km, respectively). In nature, this is the region of the boundary between the Tibet and the Southern China block. Fault-block structures and faults in the lithosphere can be viewed as geological objects that directly control epi- and hypocentral fields of earthquakes
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