ALBERT

Description: Abstract: In the Eurasian part of the World Stress Map almost the whole region east of the Tornquist-Teisseyre line is terra incognita. The closure of this information gap is of fundamental importance to the understanding of the geodynamics of the Eurasian continent. A detailed analysis of stress-induced wellbore breakouts has been performed over a 4.1-km-long depth internal in the Vorotilov drillhole (VGS). The borehole is located in the central part of the Russian platform, right in the centre of Vorotilov meteorite impact crater 60 km to the NNE of the city of Nine Novgorod. An ultrasonic borehole televiewer (BHTV) was used to obtain high-resolution acoustical images from the borehole wall. With an interactive system for analysing BHTV data the azimuth and shape of borehole breakouts occurring in the depth range of 1.3-4.8 km were analysed. A statistical analysis of the resulting orientation profile of the breakout azimuths yields an overall direction of the maximum horizontal principal stress SH of N137E +/- 15 degrees. Variations of breakout orientation with depth ranging from a few degrees up to more than 90 degrees are seen on various depth scales. The observed stress direction of N137E agrees very well with the average SH orientation of N145E in Central Europe. If this measurement is taken as representative for the Russian platform, the stress field in Russia is only slightly rotated in comparison to Central Europe. This can possibly be interpreted as indicative for the stress field to be governed by broad scale tectonic forces, such as a strong contribution from the forces exerted by the collision in the Alpine-Himalayan belt and by the Mid-Atlantic ridge.