ANALYSIS OF BOREHOLE TELEVIEWER MEASUREMENTS IN THE VOROTILOV DRILLHOLE, RUSSIA - FIRST RESULTS

In the Eurasian part of the World Stress Map almost the whole region e ast of the Tornquist-Teisseyre line is terra incognita. The closure of this information gap is of fundamental importance to the understandin g of the geodynamics of the Eurasian continent. A detailed analysis of stress-induced wellbore breakouts has been performed over a 4.1-km-lo ng depth interval in the Vorotilov drillhole (VGS). The borehole is lo cated in the central part of the Russian platform, right in the center of the Vorotilov meteorite impact crater 60 km to the NNE of the city of Nizni Novgorod, An ultrasonic borehole televiewer (BHTV) was used to obtain high-resolution acoustical images from the borehole wall. Wi th an interactive system for analyzing BHTV data the azimuth and shape of borehole breakouts occurring in the depth range of 1.3-4.8 km were analyzed. A statistical analysis of the resulting orientation profile of the breakout azimuths yields an overall direction of the maximum h orizontal principal stress S-H Of N 137 degrees E +/- 15 degrees. Vari ations of breakout orientation with depth ranging from a few degrees u p to more than 90 degrees are seen on various depth scales. The observ ed stress direction of N 137 degrees E agrees very well with the avera ge S-H Orientation of N 145 degrees E in Central Europe. If this measu rement is taken as representative for the Russian platform, the stress field in Russia is only slightly rotated in comparison to Central Eur ope. This can possibly be interpreted as indicative for the stress fie ld to be governed by broad scale tectonic forces, such as a strong con tribution from the forces exerted by the collision zone in the Alpine- Himalayan belt and by the Mid-Atlantic ridge.