Three-dimensional P-velocity model of the mantle and seismicity of Fennoscandia.

Abstract

The paper analyzes the three-dimensional P-velocity model of the mantle of North-West Europe (Fennoscandia) in order to isolate the connection of the earth's crustal earthquakes and processes in the mantle. The mantle model was obtained by the Taylor approximation method. This method does not depend on the choice of the reference model. The initial data for constructing the mantle model are the ISC bulletins for the period from 1964 to 2006. The three-dimensional P-velocity model of the mantle of the investigated territory is represented by horizontal sections at true speeds with a step of 25 km to the depth of 1100 km, longitude and latitude cross-sections in velocity discrepancies relative to the generalized average velocity for the mantle of Eurasia. Analysis of the model of the mantle under Fennoscandia allowed the construction of block divisibility of the mantle at depths of up to 300 km. The comparison between the block structure of the mantle and the location of epicenters of earthquakes confirms the confinement of the latter to the interblock zones. The work analyzes high-velocities inclined layers in the upper mantle and shows their association with crustal earthquakes. Velocities zones are distinguished in the mantle under Fennoscandia, the main feature of which is the propagation of a low-velocity subvertical layer from the middle mantle through the zone-1 into the transition zone of the upper mantle. Outputs of reduced velocities from the lower, middle mantle to the upper, possibly up to the cortex inclusive, followed by their "spreading" are called fluid domains. In the regions of spreading fluid domains, super-deep fluids are emerging, appearing as subvertical columns of the alternation of regions of elevated and reduced velocities. Super-deep fluids correspond to clusters of earthquakes.