Technogenic tectonic seismicity in Kuzbass

Abstract

Abstract This paper presents an analysis of the development of the current seismic state of the Kuznetsk coal basin, which is characterized by an increase in technogenic seismicity of different types under the influence of prolonged intensive mining operations. The development of technogenesis led to a significant increase in technogenic seismicity in the Kuznetsk Basin in the 1970–1980s, when the number of technogenic earthquakes began to exceed the number of natural earthquakes. Among the various types of induced seismicity, special attention is paid to strong technogenic tectonic earthquakes with a regional magnitude Mb ≥ 3 and, accordingly, a seismic energy release of more than 109 J, i.e., earthquakes of energy class K > 9. These small-focus earthquakes are often accompanied by destruction of underground mines, collapse of quarries and pits, damage to surface facilities and equipment, and other adverse effects. In this paper, such earthquakes are defined as technogenic tectonic to emphasize their dual origin: technogenic impacts and the subsequent relaxation of tectonic stresses. It is also noted that the Earth’s interior in Kuzbass initially had its own natural seismicity and a developed system of tectonic faults. Natural seismotectonic activity combined with constantly increasing scales of mining and explosive consumption has led to an increase in the number of technogenic seismic events and their intensity. A striking example of such an event was the 18 June, 2013 Bachat earthquake with a regional magnitude Mb = 5.8 and a seismic intensity of 7 in the epicentral zone. It was the world’s largest man-made earthquake induced by the mining of solid minerals. We consider the possible causes of this catastrophic earthquake and discuss the conditions favoring the formation of foci of such technogenic tectonic earthquakes resulting from changes in the geodynamic and hydrogeological conditions in the Earth’s crust under man-caused impacts. These induced changes in natural processes are accompanied by a change in the stress-strain state, resulting in the concentration of tectonic stresses at heterogeneities and in fault zones, which become sources of induced technogenic seismicity. The paper discusses the current period of the occurrence and increase in such anthropogenic seismicity in the Kuzbass region with increasing scales of coal mining and blasting. Over the last 20 years, the consumption of explosives at Kuzbass enterprises increased from 100–200 to 500–600 thousand tons per year, and, accordingly, the amounts of broken and transported rock increased from several million tons per year to a billion tons per year, which disturbed the dynamic equilibrium in the Earth’s crust and changed the existing field of tectonic stresses. Moreover, the continuously increasing consumption of explosives has also increased the technogenic impact on the crust structures. The location of the epicenters of large-scale blasts inducing seismic events with regional magnitudes Mb = 3.0-4.5 has made it possible to identify regions with the greatest technogenic impact in Kuzbass. Using the data of the ISC seismological catalog, we separated seismic events with the above magnitudes into day and night ones. Since blasting work is forbidden at night, night seismic events are referred to as technogenic tectonic earthquakes (night event criterion). The maximum magnitude of seismic events induced by blasting operations in the Kuznetsk Basin was estimated at Mb ≤ 4.4. The annual number of technogenic tectonic earthquakes with 3.0 ≤ Mb ≤ 3.4, 3.5 ≤ Mb ≤ 3.9, 4.0 ≤ Mb ≤ 4.4, and Mb ≥ 4.5 was determined based on the night event criterion. The regions of their occurrence were identified from the location of the epicenters of technogenic tectonic earthquakes.