Algorithm for calculating neotectonic stresses in platform areas by the structural-geomorphological method

Abstract

An algorithm for calculating stress values proposed here is based on the results of reconstruction performed by L.A. Sim’s structural-geomorphological method for platform areas. This method makes it possible to determine the orientation of the axes of principal stresses for the shear zones from the lineament analysis of satellite images and photographs and Gzovsky’s palette, and to identify the lineaments characterizing the basement active faults which are covered by sediments. It is proposed that the dataset obtained will be subjected to the algorithm of the second-stage method of Cataclastic Analysis of faulting displacements, in which the Mohr diagram is used to calculate the stress values normalized for the cohesion strength of the massif. The further determination of the cohesion strength and absolute stress values is based on the data for lithostatic pressure and fluid pressure in the fracture-pore space of the massif (either measured or prescriptive). The stress calculation algorithm was tested on a small area (60 square km of satellite imagery) near the territorial district of Seversk – the southern border of the West Siberian Platform. The calculations have shown that with the fluid pressure variations ranging from hydrostatic values to twice higher than those, the cohesion strength of a rock mass at the base of the sedimentary cover (500 m depth) is in the range of 41.0 to 16.8 bar, and the level of maximum tangential stresses lies in the range of 75 to 31 bar.