Deformations of the earth crust in Lithuania and seismic risk for buildings and structures

Abstract

The best studied area of the recent geodynamic activity in Lithuania is located in the Ignalina NPP area. Seeking to identify the intensity of the vertical movements of the earth’s crust the leveling network of total length of 66 km comprising 117 sites was established in the 1989. Six measurement cycles have been carried out since 1989 with an average quadratic error of vertical movements 0.3–0.4 mm. For investigation of horizontal movements of the earth’s crust the cosmic geodetic methods were applied. A network consisting of 10 geodetic sites was established in 1998. The positioning of the sites was adjusted taking into consideration the tectonic framework of the area. Two measurement cycles have been performed in the network. The average quadratic deflections of coordinates of sites do not exceed 0.8 mm. The horizontal movements of the earth’s crust were investigated applying the method of tensor analysis. The strains and tectonic stresses evaluated by finite element method (FEM) from geodetic observation data. They persuade that the Ignalina NPP area is situated close to the active tectonic zones, essentially the west-east trending Drūkšiai fault zone. Accordingly, the seismic risk is acknowledged. The evaluation of the seismic risk potential remains very complicated problem in Lithuania due to lack of seismic observations and poor knowledge of the fault geometries and kinematics and tectonic stresses affecting the earth’s crust.