SEISMICITY of the KOPETDAG REGION in 2015

In 2015, the seismicity of the Kopetdag region was monitored by the network of 32 seismic stations, including 28 digital and 4 analogue stations. The re-equipment of stationary analogue stations of Turkmenistan with digital GEOSIG equipment, which began in 2013, was continued in 2015 – 6 GEOSIG stations were added to 9 stations of this type, and the analogue equipment at the re-equipped stations was stopped. In 2015, the seismic activity A10 in the Kopetdag region was close to the background level for the period 1992–2014, while the number of weak events significantly exceeded the level of the previous year. The seismic activation along the boundaries of the crustal blocks in the north of the Iranian plate, which began in 2012, continued by the October 12, 2015 earthquake with KR=12.7, Mw=5.2. This strongest earthquake in the territory of Turkmenistan in 2015, named the Kenekesir earthquake by the name of the nearest settlement, accompanied by numerous aftershocks – more than 35000 events with KR=3–11 were located during 80 days after the mainshock within 30 km radius. The aftershock series lasted 186 days and ended in 2016. According to the complex of instrumental seismological and tectonic data, oblique-slip with equal normal and strike-slip components occurred in the source of the mainshock. The rupture plane had a southwestern strike and dipped to the northwest. The maximum ("Bath’s") aftershock occurred on November 16 with KR=11.1. Judging by its remoteness from the mainshock in space and time, and the difference in the type of movement in the source (upthrust), it was caused by stress relaxation in the environment.

Monitoring the dynamics of seismicity within the Kemin-Chilik zone, generating M≥8 earthquakes

The dynamics of seismic processes at the junction of the Tien Shan mountain building area and the Kazakh shield is presented in the paper. It is noted that the Tien Shan’s lithosphere over thrusts the Kazakh Shield’s lithosphere, and the Kazakh Shield’s lithosphere under thrusts beneath the Tien Shan’s lithosphere based on the seismic tomographic and seismotectonic data. Low-velocity heterogeneity is distinguished at the junction of these lithospheres, under where a low-velocity anomaly flow is assumed in the mantle. Marginal (active structures of the Ili basin, Zaili mountain range), and middle (active structures of the Kemin, Chilik basins, Kungei mountain range) subzones with characteristic seismicity and seismic regimes are formed here. Seismogenic zones are distinguished (from north to south): Predzaili, Kemin-Chilik, Predkungei. Powerful earthquakes with M>8 occur in the Kemin-Chilik seismogenic zone (about 250 km long and up to 25 km wide), and earthquakes with M=7-8 - in the Predza-ili and Predkungei seismogenic zones. The dynamics of the earthquakes’ sequence is predetermined by the dynamics of the hierarchy of faults and blocks in the junction zone. The sequence of earthquakes is expressed by the hierarchy of seismic cycles. Seismic activation period, a peak of seismic activation, a period of seismic activation’s decay, and seismic calm period are distinguished in every cycle. Strong earthquakes take place in a first-order cycle with a long period, significant and small earthquakes - in cycles with corresponding short periods. The seismicity level of the study area is determined by the trajectory of the seismic cycles’ association. Dynamic segmentation and dynamic sectorization, vectors of seismic activity directed from the east and west to the highly compressed central part of the region are noted in the spatial and temporal distribution of earthquakes at the junction of the Tien Shan and the Kazakh shield.

Bachatskiy induced earthquake on June 18, 2013, ML=6.1, I0=7 (Kuzbass)

The Bachatsky earthquake of 18 June 2013 and a seismic activation of the same name coal strip mine, started several years before the earthquake and still persists today, have been studied using temporal local seismic arrays in the area. It was found experimentally that the seismic process area is closely connected to open workings, and the earthquakes are extend-ed from the working bed to a depth of 4-5 km. Adjacent to the mine depression sedimentary rocks were activated. The technogenic seismic regime is continuous and not stationary: intervals of background seismicity with relatively weak and seldom events are disturbed by bursts of activity with a rise in the magnitude of stronger earthquakes and frequency of occurrence of weak events. The seismic activation may last for 1–3 months. During the last five years, four seismic activations have been recorded, three of which were generated by large earthquakes of 09.02.2012, ML4.3; 04.03.2013, ML3.9; 18.06.2013, ML6.1. The last one was completed by a series of perceptible earthquakes with local magnitude of 3.0–3.5. The focal mechanism of the Bachatsky earthquake is a thrust fault with one of the motion planes corresponding to the anthropogenic impact. The earthquake flow forms a single process in the space with the b-value of the Gutenberg-Richter relationship different from the natural seismicity. The studied induced seismicity does not correspond to the structural regularities of natural seismicity in the Altai-Sayan mountain area. The findings prove that the Bachatsky earthquake and associated activation can be considered as man-made events.

RELATION BETWEEN PERIODS OF SEISMIC ACTIVATION IN THE SEISMICALLY ACTIVE ZONES OF UZBEKISTAN AND THE OCCURRENCE OF STRONGEST EARTHQUAKES IN CENTRAL ASIA

method for studying the influence of seismic activation, which began in one of the seismically active zones, on the possibility of seismic activation in other seismically active zones of region is proposed. The method is based on: studying the time function of released seismic energy in each seismically active zone; choosing of its threshold values; specifying an alarm function and estimating the statistical significance of the difference between a share of earthquakes from the various seismically active zones falling within the alarm intervals and a share of the alarm time in this seismically active zone. It was established which of the Central Asian seismically active zones affect the activation of the main Uzbekistan seismically active zones the most. Inversely, for each of the most significant Central Asian seismically active zones it was established on which one of the Uzbekistan seismically active zones Central Asian zones have the greatest impact. It was suggested that synchronous seismic activation manifestations are observed in seismically active zones of close strike with geometrically similar active fault lines and located close to each other. The revealed relationships are important for understanding the interaction nature of various seismotectonic structures, but they cannot be used in forecasting as a determinative factor. This information has to be used in a complex with data of prognostic monitoring in various geophysical fields. Activation of Central Asian highly potential zones can act as a trigger in certain seismically active zones of Uzbekistan, where the significant supply of elastic energy is already accumulated.

ABOUT THE ROLE OF TECTONIC DISORDERS IN THE DEVELOPMENT OF INSPECTED SEISMICITY FROM JOINT EXPOSURE TO OPEN AND UNDERGROUND WORKS ON THE PRODUCTION OF COAL

According to the results of monitoring with a temporary network of seismological stations in the south of Kuzbass in the area of seismic activation of technogenic nature, formed under the simultaneous influence of open and underground coal mining, the spatial structure of activation, its development in time and connection with tectonic disturbances are studied in detail. Seismic activation near underground workings is distinguished by locality in area, a large number of earthquakes with magnitudes Ml ≤ 2. For three closely spaced coal mines, there is a general seismic activation, inside of which, as a local zone, there is the activation of underground workings, characterized by the strongest earthquakes with Ml in the range of 3 ÷ 4. Depths of foci have a two-modal distribution with maxima in the range of 1 ÷ 1,5 km and in the range of 2 ÷ 3 km. Both in the area of mines and in the area of open mine workings, the subsoil is significantly deeper than the mine workings seismically activated. The seismic process in time is not stationary and pulsating.