Elena Kozlovskaya

Complex lithospheric structure under the central Baltic Shield from surface wave tomography

Complex lithospheric structure under the central Baltic Shield from surface wave tomography

EUROBRIDGE: New insight into the geodynamic evolution of the East European Craton

Abstract The Palaeoproterozoic crust and upper mantle in the region between the Ukrainian and Baltic shields of the East European Craton were built up finally during collision of the previously independent Fennoscandian and Sarmatian crustal segments at c. 1.8-1.7 Ga. EUROBRIDGE seismic profiling and geophysical modelling across the southwestern part of the Craton suggest that the Central Belarus Suture Zone is the junction between the two colliding segments. This junction is marked by strong deformation of the crust and the presence of a metamorphic core complex. At 1.80-1.74 Ga, major late to post-collisional extension and magmatism affected the part of Sarmatia adjoining the Central Belarus Zone and generated a high-velocity layer at the base of the crust. Other sutures separating terranes of different ages are found within Sarmatia and in the Polish-Lithuanian part of Fennoscandia. While Fennoscandia and Sarmatia were still a long distance apart, orogeny was dominantly accretionary. The accreted Palaeoproterozoic terranes in the Baltic-Belarus region of Fennoscandia are all younger than 2.0 Ga (2.0-1.9, 1.90-1.85 and 1.84-1.82 Ga), whereas those in Sarmatia have ages of c. 2.2-2.1 and 2.0-1.95 Ga. Lithospheric deformation and magmatism at c. 1.50-1.45 Ga, and Devonian rifting, are also defined by the EUROBRIDGE seismic and gravity models.

DynaQlim – Upper Mantle Dynamics and Quaternary Climate in Cratonic Areas

The isostatic adjustment of the solid Earth to the glacial loading (GIA, Glacial Isostatic Adjustment) with its temporal signature offers a great opportunity to retrieve information of Earth’s upper mantle to the changing mass of glaciers and ice sheets, which in turn is driven by variations in Quaternary climate. DynaQlim (Upper Mantle Dynamics and Quaternary Climate in Cratonic Areas) has its focus to study the relations between upper mantle dynamics, its composition and physical properties, temperature, rheology, and Quaternary climate. Its regional focus lies on the cratonic areas of northern Canada and Scandinavia.

Lithosphere structure along the northern part of EUROBRIDGE in Lithuania; results from integrated interpretation of DSS and gravity data

Abstract In the summer of 1995, the first on-shore phase of the EUROBRIDGE DSS experiment took place in Lithuania. The quality of recordings was good and contained clear P-wave reflections from inter-crustal interfaces and the Moho boundary. Very clear reflections were also registered from the interface below the Moho boundary. The arrivals of both reflected and refracted P-waves from 10 shotpoints were processed using the seis 83 ray-tracing program. As a result, a 2-D seismic model along the Lithuanian part of EUROBRIDGE has been obtained. The comparison of synthetic and experimental seismograms showed good agreement of the model with registered travel times. To visualise better the existing tectonic discontinuities, an integrated 2-D seismic and density model along the northern part of EUROBRIDGE was compiled. For this purpose, the technique of gravity data inversion based on a non-linear relationship between density and seismic P-wave velocity was used. This integrated velocity–density model helped to reveal differences in deep lithosphere structure beneath the northern part of EUROBRIDGE where the tectonic contact of two Proterozoic terrains is located.

An algorithm of geophysical data inversion based on non-probabilistic presentation of a priori information and definition of Pareto-optimality

This paper presents an inversion algorithm that can be used to solve a wide range of geophysical nonlinear inverse problems. The algorithm in based upon the principle of a direct search for the optimal solution in the parameter space. The main difference of the algorithm from existing techniques such as genetic algorithms and simulated annealing is that the optimum search is performed under control of a priori information formulated as a fuzzy set in the parameter space. In such a formulation the inverse problem becomes a multiobjective optimization problem with two objective functions, one of them is a membership function of the fuzzy set of feasible solutions, the other is the conditional probability density function of the observed data. The solution to such a problem is a set of Pareto optimal solutions that is constructed in the parameter space by a three-stage search procedure. The advantage of the proposed technique is that it provides the possibility of involving a wide range of non-probabilistic a priori information into the inversion procedure and can be applied to the solution of strongly nonlinear problems. It allows one to decrease the number of forward-problem calculations due to selective sampling of trial points from the parameter space. The properties of the algorithm are illustrated with an application to a local earthquake hypocentre location problem with synthetic and real data.

Study of Local Seismic Events in Lithuania and Adjacent Areas Using Data from the PASSEQ Experiment

The territory of Lithuania and adjacent areas of the East European Craton have always been considered a region of low seismicity. Two recent earthquakes with magnitudes of more than 5 in the Kaliningrad District (Russian Federation) on 21 September 2004 motivated re-evaluation of the seismic hazard in Lithuania and adjacent territories. A new opportunity to study seismicity in the region is provided by the PASSEQ (Pasive Seismic Experiment) project that aimed to study the lithosphere–asthenosphere structure around the Trans-European Suture Zone. Twenty-six seismic stations of the PASSEQ temporary seismic array were installed in the territory of Lithuania. The stations recorded a number of local and regional seismic events originating from Lithuania and adjacent areas. This data can be used to answer the question of whether there exist seismically active tectonic zones in Lithuania that could be potentially hazardous for critical industrial facilities. Therefore, the aim of this paper is to find any natural tectonic seismic events in Lithuania and to obtain more general view of seismicity in the region. In order to do this, we make a manual review of the continuous data recorded by the PASSEQ seismic stations in Lithuania. From the good quality data, we select and relocate 45 local seismic events using the well-known LocSAT and VELEST location algortithms. In order to discriminate between possible natural events, underwater explosions and on-shore blasts, we analyse spatial distribution of epicenters and temporal distribution of origin times and perform both visual analysis of waveforms and spectral analysis of recordings. We show that the relocated seismic events can be grouped into five clusters (groups) according to their epicenter coordinates and origin and that several seismic events might be of tectonic origin. We also show that several events from the off-shore region in the Baltic Sea (at the coasts of the Kaliningrad District of the Russian Federation) are non-volcanic tremors, although the origin of these tremor-type events is not clear.