EVIDENCE FOR A SEISMOGENIC UPPER MANTLE AND LOWER CRUST IN THE BAIKAL RIFT

The high level seismicity of the Baikal rift zone and its spatial distribution in dense swarms and belts provide an opportunity to study the seismogenic behaviour of a continental lithosphere submitted to extension in an early stage. Using data from a regional seismological network, we analyze a significantly large set of events from an earthquake swarm located east of the nearly aseismic northern Baikal lake. We find that at least 10% of the well-constrained events are located in the lower crust or the uppermost mantle. The fault plane solutions of earthquakes within the crust define a NW-SE extensional stress regime perpendicular to the rift axis. Our results confirm the idea that zones of continental extension may exhibit significant rigidity. We propose to infer a migration of deformation from the northern Baikal lake to an initially stronger part of the lithosphere, i.e. the Barguzin rift and its extension to the east.