Abstract: There is an active tectonic zone in large scale in Altai region of the Asian continent, and historical earthquake data shows that the Altai Mountain is also active in seismicity. Analyzing the current stress state is of greatsignificance to the assessment of earthquake activity risk. In this research, the distribution law of current in-situstress state in the active fault zone is revealed by hydraulic fracturing measurement at two boreholes (nearly 700 m in depth) in the piedmont of Altai Mountains. Results show that in buried depth of about 320 m, the spatial principal stress state changes from thrust type to strike-slip type, indicating a stress partition near the active faults; the orientation of maximum horizontal principal stress of the two boreholes is mostly in NW, which, together with the focal mechanism, verifies the right-lateral strike-slip characteristics of NWW active faults. Finally, according to the measured stress data, mechanical analysis on the stability of the active faults is carried out based on Coulomb faulting criterion and the law of Byerlee. Results conclude that up until now, the active faults in the piedmont of the Altai Mountains are relatively stable, with no mechanical condition brewing instability. The research results offer basic geomechanics data for studies on the regional active faults’ current activity, and provide scientific reference for selecting the location of engineering project near the active faults.

Key words: Altai Mountains, active fault, in-situ stress, the law of Byerlee, stability