Seismotectonic characteristics of the northern flank and axial part of the Tajik Depression (the Garm Geodynamic Research Area)

Abstract

Detailed estimates of seismotectonic strain (STS) characteristics are obtained for the upper crust from focal mechanisms of numerous earthquakes (M ≥ 1) in the northern and axial parts of the Tajik Depression (the Garm area, Tajikistan). It is shown that, in the majority of cases, a close interrelation exists between tectonic structures and the STS type. Changes in the STS characteristics in various areas of the depression admit a reasonable geological interpretation. Based on geological, seismological, and geodetic data, a unified scheme of deformation of layered rocks of the Tajik Depression is presented. The main factor controlling the deformation process is the extrusion of the rocks in the axial part of the depression in the NNW and SSE directions (with the formation of imbricate thrusts) and in the WSW direction. The latter case is characterized by left-lateral motions in fault zones in the south of the depression (including the Darvaz fault) and by right-lateral motions in northern zones (the Peter the First Range) located from seismological data. In our opinion, such expulsion is caused mainly by an increase of the volume of layered rocks in the Tajik Depression, apparently due to deep fluids penetrating into these rocks and supplying additional mineral material. However, it is also possible that the region is influenced, to an extent, by the general subhorizontal N-S compression associated with the convergence of the Indian and Eurasian lithospheric plates in accordance with the concept of plate tectonics.