Geophysical processes and biosphere: article

Аnnotation: In 2003 catastrophic earthquake (magnitude of 7.3) occurred near the southwestern border of the Chuya and Kurai depressions in South-Eastern Altai. In this study we analyzed seismic activity of this area and compared the modern and neotectonic stresses of the southeastern Altai. A scheme representing the direction of the compressive stress of the Chui-Kurai depression and the framing structures was drawn. Structural-geomorphological method was performed in order to reconstruct neotectonic stress. The results show the shift of orientation of the 1st rank subhorizontal compression axis from meridional to NNE and NE. Within the region where the earthquake occurred, it was found that the largest faults of the grade I were activated at the neotectonic stage in an environment of additional compression. A larger-scale stress field has been reconstructed for the Chagan-Uzun rigid block that delineates the Chui and Kurai depressions. The neotectonic fault of the NW strike (designated as Nameless), bounding the Chui and Kurai depressions from the south, has been identified. Nameless fault is divided by smaller faults of the SE-orientation into three segments. Accord-ing to the data on the mechanisms of strong earthquake foci in the investigated region, a stable near-horizontal position of the compression axis was established (as well as at the neotectonic stage). The analysis of earthquake mechanisms reveals mainly upwelling mechanisms within the Chagan-Uzun elevated block. This may be due to the ongoing uplift of the Chagan-Uzun block at the current stage. Along Nameless fault in the NW and to a lesser extent in the SE, the mechanisms of earthquake foci of the shear type. Major seismic events occur mainly in a compression environment. Thus, the Chuya earthquake is caused by the environment of subhorizontal compression (both regional and local), which is determined by comparing neotectonic and modern stresses.