SEISMICITY of NORTHERN EURASIA in 2015

The review of the Northern Eurasia seismicity for 2015 includes a description of seismic networks, the results of analysis of the seismic regime and individual noticeable earthquakes in 16 regions of Russia and neighbouring countries. Seismic monitoring was carried out by the networks of seismic station of Russia, Azerbaijan, Armenia, Belarus, Kazakhstan, Kyrgyzstan, Latvia, Moldova, Turkmenistan, Tajikistan, Uzbekistan, Ukraine, including 599 digital, 7 analogue stations and eight seismic groups. In 2015, these networks registered about 27 thousand tectonic earthquakes, over 6 thousand volcanic earthquakes, 599 explosions, 23 mountain-tectonic shocks and induced earthquakes. Focal mechanisms of 592 earthquakes were determined, the information on manifestations of 449 perceptible earthquakes was collected. 26 shocks were felt in settlements of Northern Eurasia with an intensity Ii≥5. According to estimates of the annual number and released seismic energy in 2015 in comparison with the long-term characteristics of the seismic regime, the seismic process in most regions of Northern Eurasia proceeded in the “background” regime. An exception is Tajikistan and adjacent territories, where two strong earthquakes occurred – the Hindu Kush earthquake on October 26 with Mw=7.5, h=230 km in northern Afghanistan, near the border with Tajikistan, and the Sarez earthquake on December 7 with Mw=7.2, Ms=7.6, h=20 km in Tajikistan. Both earthquakes were accompanied by numerous aftershocks and were felt in Tajikistan with intensities Imax=7 and Imax=7–8 respectively, on the MSK-64 scale. Notable event on the territory of Northern Eurasia in 2015 is the emergence of the Muyakan sequence of earthquakes, the largest for the period of instrumental observations in the region "Baikal and Transbaikalia", as a result of which the number of recorded earthquakes in the region quadrupled concerning 2014. The other interesting fact is occurrence of tangible earthquakes in the regions, traditionally considered weakly seismic – near the Semipalatinsk test area in Eastern Kazakhstan (Chingiz earthquake on January 20, Ms=4.1, I0=5–6), in the Middle Urals (Middle Ural earthquake on October 18 with ML=4.7, I0=6) and in the southwest of East -European platform (Poltava earthquake on February 3 with KR=10.7, I0=6).

Methods and results of long-term strong earthquakes forecast in the Uzbekistan territory

An approach to evaluate the current seismological situation in the Uzbekistan territory is presented. This approach is based on the regularities of seismic processes in strong-earthquake focal areas and the manifestation peculiarities of strong earthquakes in seismically active zones. At the first stage, within seismically active zones, areas with a high seismic activity matching the strong earthquake level were identified during the historical and instrumental observation periods. Considering the low variability in the direction of seismotectonic processes over tens and hundreds of years, which determines the modern stress state of seismically active structures, these areas were considered the most likely areas to experience strong earthquakes over the next few decades. Tectonophysical validation of the division of seismically active zones into areas with different potential hazards of strong earthquakes was carried out within the framework of cataclastic analysis method of rupture dislocations (CAM). At the second stage, temporal fluctuations in seismic regime parameters within the selected areas were studied. Based on the number of current anomalous features identified, the areas were ranked according to the occurrence probability of strong earthquakes over the next few years.

On the stability of the seismic mode parameters in time by the example of the east of the central part of Northern Caucasus

The parameters of the seismic regime of the eastern zone of the Central Caucasus are deter-mined based on the new catalog data. A similar study is being carried out for the third time: in 1996, 2015 and 2021. The basis for work in the area surrounding Grozny was laid in 1996 by a comprehensive study of geological, geomorphological, geophysical and seismological ma-terials. When comparing the results, the stability of the seismic regime parameters was estab-lished: the repetition schedule b and seismic activity A3.3 near Grozny, the capital of the Che-chen Republic and a large industrial center in 2015 and 2021. In both cases, the estimates were performed on the same the same territory bounded by coordinates: 41.1-45.6N and 42.6-48.8E. The same basic earthquake catalog was used for the calculations. The difference was in the number of events that took place in this territory from 2015 to 2020 inclusive.

Influence of development of raw hydrocarbon deposits on the geodynamic state and seismic regime of the Earth's crust in the Southern Urals

The article presents the results of the analysis of the impact of field development on the geody-namic state and seismic activity of the earth's crust of the Southern Urals, were compared in field development, anthropogenic changes in the bowels of district fields with the level of seismic ac-tivity, correlation between indicators of development of deposits and the parameters of the seis-mic activity of the earth's crust and the statistical analysis of the seismic regime of the area de-posits of hydrocarbon raw materials. Correlation analysis of field development indicators and seismic activity parameters revealed an almost linear relationship (r>0.9) between reservoir pres-sure and the number of events (including low-energy pulse events) and a close relationship be-tween the average debit and the number of events. A model of the seismic activity of hydrocar-bon deposits in the Southern Urals is constructed in the form of a set of graphs of the frequency of seismic events and changes in their angle of inclination. The constructed model indicates a change in the nature of seismic activity in the subsurface of the field area, which consists in a de-crease in the energy of events and an increase in their number. The cyclical nature of seismic ac-tivity on the territory of the Orenburg oil and gas condensate field (OOGCF) is revealed. Current-ly, there is an accumulation of stress associated with the continued drop in reservoir pressure during the field operation and natural tectonic processes against the background of a decrease in the rate of hydrocarbon production. Reducing production volumes at OOGCF does not reduce the man-made load on the Earth's crust, but reduces the rate of stress accumulation. This leads to a decrease in the energy of seismic events and an increase in their number (taking into account the pulses).

Results of seismological observations on the territory of the Republic of North Ossetia-Alania and adjacent areas in 2020

North-Ossetian Division of the Geophysical Survey of the Russian Academy of Sciences (NOD GS RAS) carries out the continuous seismological observations of the central part of the North Caucasus region. The branch's seismological network includes 12 observation points located on the territory of the Republic of North Ossetia-Alania. The paper provides basic information about the places of installation of seismic stations and their equipment, and notes the registration possibilities of the network. The total number of registered seismic events and separately within the administrative territories in 2020 is given. The total released seismic energy is calculated. A comparison of the energy indicator with the previous year is given. The schedule of repeatability is calculated and constructed, which indicates the level of reliability of event registration. The analysis of the earthquakes foci distribution with ref-erence to geotectonic structures is presented on the map of the epicenters of recorded seismic events with an indication of the distribution against the background of the focal zones. Iden-tified and described the swarm sequences of seismic events, which occurred in the territories of the Republics of North Ossetia-Alania and Kabardino-Balkaria, as well as in the Stavropol Territory. The mechanisms of the foci for the three most powerful earthquakes are deter-mined and their stereograms are given. The obtained results will allow us to study the chang-es in the seismic regime of the North Caucasus region more effectively.

Estimation earthquake occurrence probability in Kamchatka region based on seismological and complex of ionospheric precursors

In this paper the authors present the method of estimation of a region, waiting period and probability of strong earthquakes with KS ≥ 13.5 (M ≥ 6.0) in Kamchatka region based on the combination of mid-term and short-term predictive signs accompanying earthquake formation. The seismological predictive parameter ξP was taken as a mid-term precursor. It was calculated on the basis of the probabilistic model of seismic regime. A complex of ionospheric parameters was considered as short-term predictive signs with an earthquake waiting period of up to 5 days. It includes the K-layer, the sporadic Es layer of the r type, the critical frequency foF2, and the frequency stratification of the F2 layer. The probabilities of strong earthquakes with KS ≥ 13.5 (M ≥ 6.0) that occurred over the period 2019–2021 in an expected zone, determined by the parameter ξP, were estimated on the basis of Bayes method provided that a complex of anomalous parameters of the ionosphere was identified.

SEISMICITY OF NORTHERN EURASIA in 2014

An overview of Northern Eurasia seismicity in 2014 is given. This territory includes 16 regions of Russia and neighboring countries. Seismic monitoring was carried out by 618 stationary seismic stations, including 591 digital, 27 analog stations and eight seismic groups. Also, temporary stations operated in some re-gions. These networks have registered over 30 thousand tectonic and volcanic earthquakes, for 571 of them the focal mechanisms are determined. According to the data collected and presented in the Annual, 413 earthquakes were felt in settlements of Northern Eurasia in 2014, manifestations of 14 of them were surveyed and described in the special articles of this issue, together with data on the focal mechanisms, preceding seismicity, aftershock processes and seismotectonic conditions. Estimates of the number of earthquakes and seismic energy released in 2014 in the regions of Northern Eurasia in comparison with long-term characteristics of seismic regime indicate that in most regions the seismic process proceeded in the “background” or “background lowered” regimes accor-ding to the definition on the SOUS'09 scale. Only the level of seismicity in the Pribaikalye and Transbaikalia region is assessed as “background increased”. The intensification of seismicity in the source zones of the past strongest earthquakes in the Alpine-Himalayan collision-fold belt – Crimean 1927, Spitak 1988, Zakatala 2012 – is noted. The tangible earthquakes that occurred in the previously aseismic areas of the Siberian and Turan platforms – Gonam earthquake on January 4 with KP=14.2, I0=8, Boguchan earthquake on January 17 with KP=13.3, I0=7 and Karaganda earthquake on June 21 with KP=11.7, I0=5–6 – indicate the need to revise the concept of a low seismic hazard in these platform areas.

SAKHALIN

A review of the Sakhalin seismicity in 2014 based on the data of regional network is given. The network included four stationary and ten temporary digital seismic stations. This network was supported by ten stations of local network operating in the south of Sakhalin. Parameters of 450 seismic events, including 25 explosions, and focal mechanisms for 4 events are determined. 22 earthquakes had a macroseismic effect. The map of earthquake completeness and the map of epicenters are given. The distribution of crust and deep earthquakes on magnitude and their summarized energy for seven seismoactive areas in comparison with average parameters for 2001–2013 are presented. For each area and the region as a whole, an analysis of the seismic regime parameters in 2014 in comparison with long-term parameters is given, tangible and strong earthquakes are described. The seismicity of the Sakhalin region in 2014 can be characterized as a moderate one. Somewhat increased seismic activity was recorded in the East Sakhalin and Southeastern areas.