Stress State of the Earth’s Crust, Seismicity, and Prospects for Long-Term Forecast of Strong Earthquakes in Uzbekistan

Abstract

Abstract —The current stress state of the Earth’s crust on the territory of Uzbekistan is studied using algorithms from the cataclastic analysis of displacements (CAD) with the application of a combined catalog of earthquake source mechanisms. The axis of maximum compression is nearly horizontal and orthogonal to the strike of tectonic structures for the larger part of the area under study, and the angle of penetration of the axis of minimum compression varies greatly for different parts of the territory. The areal distribution of the Lode–Nadai coefficient indicates the predominance of a stress state close to pure shift for the area under study. Without differentiation of the seismically active bed by depth, almost the entire territory of Uzbekistan is characterized by a geodynamic stress state corresponding to horizontal compression. There are significant differences in the stress state parameters for different deep beds of the Earth’s crust. With account for the representative recording periods of seismic events of different energy levels, the earthquake recurrence parameters for the entire territory as a whole and large seismically active zones are determined. It has been established that the epicenters of strong earthquakes recorded since the historical time are grouped in compact areas with linear dimensions of 50–80 km. The tectonophysical interpretation of the selected areas is given within the framework of the CAD, in which it is noted that strong earthquakes occur mainly in areas of lower effective confining pressure and maximum tangent stresses. This is due to the fact that the values of friction forces at faults in such areas are low, which creates the most favorable conditions for large-scale destruction. According to the results of the reconstruction of the natural stresses of the CAD, such areas on the territory of Uzbekistan are identified within faults and flexural-fault zones in South Fergana and North Fergana, as well as in the Gazli region. The current seismological situation in the selected areas of long-term forecast is estimated using a set of prognostic parameters of the seismic regime, and a map of the areas of expected seismic activity is compiled. The analysis of previous forecast maps developed within the framework of the presented approach shows high value in their information.