Stress State of Uzbekistan’s Seismically Active Areas

Abstract

The current stress state of the Earth’s crust in the territory of Uzbekistan was studied by cataclastic analysis of displacements along fault sets for the collected catalog of earthquake focal mechanisms (EFM), compiled from the data of different authors. Two stages of stress field reconstruction are implemented at different levels of area detail of averaging parameters and for different magnitude hierarchies of the analyzed earthquakes. Azimuths and dip angles of principal stresses axes, Lode–Nadai coefficient values, geodynamic type of stress state, relative (normalized to the cohesion strength of the rock massif) normalized values of the maximum shear stress and effective pressure are determined for different areas of the studied territory. As a result of natural stress reconstructions based on the focal mechanisms of earthquakes with magnitudes M ≤ 4.5 and M ≥ 5, differences in the parameters of the stressed state were revealed. It has been suggested that the hierarchy of magnitude levels of the considered earthquakes reflects the stressed state of various deep layers of the crust. It is shown that strong earthquakes gravitate to zones of reduced effective pressure. On this basis, segments of active faults have been identified in the territory of eastern Uzbekistan, which are considered zones of potentially increased seismic hazard.