SEISMICITY of the NORTH-EAST of RUSSIA in 2015

The results of seismic monitoring of the Magadan oblast, the Chukotka Autonomous okrug, and the shelves of the adjacent seas (Okhotsk, Chukchi, Bering, and East Siberian seas) are considered. There were 14 seismic stations working in the region. The new station “Gadlya” was opened on the Okhotsk sea coast. The catalog includes information about 290 earthquakes with energy classes KR=4.4–12.6. As usual, most of them (93 %) are localized in the Kolyma region. The total seismic energy released within the region’s borders was ΣЕ=4.6341012 J. According to the earthquake energy completeness map Кmin built for the region, minimal energy level of earthquakes, Кmin=5.0, is provided at two areas near the Susuman and Magadan stations. The station network can register without omissions the earthquakes with Kmin≥8 at the Okhotsk sea and Kolyma areas, with Kmin≥10.6 in the Chukotka area. In 2015 three earthquakes with intensities I=2–4 by MSK-64 scale were felt in settlements of North East of Russia. The 2015 strongest earthquake occurred on June 1 at 10h53m with KR=12.6 (MPSP=4.9), h=31 km in the Kolyma area. A maximum shaking intensity of I=4 was observed in Omsukchan settlement (∆=132 km). In March 2015 a swarm of 29 weak earthquakes with KR=6.2–9.8 occurred northeast of Talaya settlement. Epicenters of Kolyma area earthquakes were plotted on the tectonic zoning map of the Magadan region. Most earthquakes are confined to the main deep faults oriented in the northeastern and sublatitudinal directions. All hypocenters are located within the Earth's crust. The seismicity level of the North-East of Russia in 2015 according to the “SOUS09” scale was assessed as "background average" for the observation period from 1968 to 2015. Spatially, all earthquakes in the North-East of Russia are traditionally concentrated within the major seismogenic belts – Chersky, North-Okhotsk, and Trans-Beringian.

System-Analytical Method of Earthquake-Prone Areas Recognition

Typically, strong earthquakes do not occur over the entire territory of the seismically active region. Recognition of areas where they may occur is a critical step in seismic hazard assessment studies. For half a century, the Earthquake-Prone Areas (EPA) approach, developed by the famous Soviet academicians I.M. Gelfand and V.I. Keilis-Borok, was used to recognize areas prone to strong earthquakes. For the modern development of ideas that form the basis of the EPA method, new mathematical methods of pattern recognition are proposed. They were developed by the authors to overcome the difficulties that arise today when using the EPA approach in its classic version. So, firstly, a scheme for the recognition of high seismicity disjunctive nodes and the vicinities of axis intersections of the morphostructural lineaments was created with only one high seismicity learning class. Secondly, the system-analytical method FCAZ (Formalized Clustering and Zoning) has been developed. It uses the epicenters of fairly weak earthquakes as recognition objects. This makes it possible to develop the recognition result of areas prone to strong earthquakes after the appearance of epicenters of new weak earthquakes and, thereby, to repeatedly correct the results over time. It is shown that the creation of the FCAZ method for the first time made it possible to consider the classical problem of earthquake-prone areas recognition from the point of view of advanced systems analysis. The new mathematical recognition methods proposed in the article have made it possible to successfully identify earthquake-prone areas on the continents of North and South America, Eurasia, and in the subduction zones of the Pacific Rim.

System-analytical method of strong earthquake-prone areas recognition

<p>Proper seismic hazard assessment is the most important scientific problem of seismology, and geophysics in general. With the development of the world economy, the importance of the problem grows and acquires global significance.</p><p>Strong earthquakes (M ≥ M<sub>0</sub>, M<sub>0</sub> is the magnitude threshold starting from which earthquakes in the studied region are considered strong), as a rule, do not occur over the entire territory of the seismic region. Accordingly, the recognition of areas prone to future strong earthquakes is an urgent fundamental direction in research on the assessment of seismic hazard. Identification of potentially high seismicity zones in seismically active regions is important from both theoretical, and practical points of view. The currently available methods for recognition of high seismicity zones do not allow repeatedly correcting their results over time due to the invariability of the used set of recognition objects. In this work, a new system-analytical approach FCAZ (Formalized Clustering And Zoning) to the problem has been created. It uses the epicenters of rather weak earthquakes (M ≥ M<sub>R</sub>, M<sub>R</sub> is a certain magnitude threshold of weak earthquakes) as objects of recognition. This makes it possible to develop the recognition result of zones with increased seismic hazard after the appearance of new earthquake epicenters. The latter makes FCAZ a method of systems analysis.</p><p>The system-analytical method for analyzing geophysical data developed by the authors has led to the successful recognition of areas prone to the strongest, strong, and most significant earthquakes on the continents of North, and South America, Eurasia, and in the subduction zones of the Pacific Rim. At the same time, in particular, for the classical approach of strong earthquake-prone areas recognition EPA (Earthquake-Prone Areas), a new paradigm for recognition of high seismicity disjunctive nodes, and lineament intersections with training by one “reliable” class was created in the work.</p><p>In the regions studied in this work, FCAZ zones occupy a relatively small area compared to the field of general seismicity – 30% – 40% of the area of all seismicity, and 50% – 65% of the area where earthquakes with M ≥ M<sub>R</sub> occur. This illustrates the spatial nontriviality of the FCAZ results obtained in this work. The results of the work also show that weak seismicity can actually “manifest” the properties of geophysical fields, which in the classical EPA approach are used directly as characteristics of recognition objects (disjunctive nodes or intersections of the axes of morphostructural lineaments).</p><p>The reported study was funded by RFBR, project number 20-35-70054 «Systems approach to recognition algorithms for seismic hazard assessment».</p>

The processing results of the vibration records from the dams and coastal slopes of the Charvak and Andijan water reservoirs of Uzbekistan during the weak earthquakes

The article discusses the processing results of the vibration records from the dams and coastal slopes of the Charvak and Andijan water reservoirs of Uzbekistan during the weak earthquakes. It is shown, that the seismic monitoring systems were upgraded at the investigated objects. Analyzing seismic estimates, revealed, that the construction of the Charvak reservoir dam has a non-linear behavior, and it is manifested in the differences of the frequency range and transmission coefficient of the dam elements. According to the analysis of seismic data, obtained during the registration of weak earthquakes at the several measuring points of dams and coastal slopes of the Charvak and Andijan reservoirs, the vibration frequencies and the ratio of the vibration velocity amplitudes to the vibration velocity amplitudes of the reference station are varies greatly depending on the azimuth to the epicenter

The Gagatli swarm of weak earthquakes - seismo activity manifestation of the Andean fault

The swarm of more than a hundred weak earthquakes, the bulk of which occurred in the second decade of January 2019, was recorded at the end of 2018 and at the beginning of 2019 in the area of the western borders of the Dagestan salient. Refinement of the position of the epicenters of the swarm events by the method of double differences showed their compact location to the northeast of the village Gagatli on the eastern latitudinal branch of the Andean fault, known for left-lateral strike-slip and normal fault kinematics. According to the results of the study of the fault plane solutions of the five most strong earthquakes in the swarm, the type of movement was established - a left-lateral strike-slip and normal component, which allowed the investigated activation to be attributed to the discharge of accumulated stresses in the eastern part of the Andean fault. A characteristic feature of the recordings of these events by the nearest stations located in the territory of Dagestan and Chechnya was the similarity of the wave pattern, established when they correlated in different frequency bands (1-2 Hz, 1-3 Hz, 1-5 Hz). The correlation matrix of the records of 19 events filtered in the 1-3 Hz band was used to construct cluster analysis dendrograms showing different correlation of the events of the swarm and other earthquakes of Dagestan at a similar distance.

NORTHERN CAUCASUS

. It is reported that 59 seismic stations operated in the region in 2013. In the western and eastern parts of the region, new stations equipped with Russian digital equipment UGRA were opened: Aibga, Fisht, Karaman. The seismic network recorded 1941 earthquakes and 34 explosions in industrial quarries. 37 earthquakes were felt in the settlements of the Caucasus. The maximum shaking intensity, equal to Imax=6 on the MSK-64 scale, was felt during earthquakes on April 16 at 12h26m with КР=11.8 in the settlements of Kichi-Gamri, Mamaul, Myurego of Dagestan. Swarms of weak earthquakes with КР=4–8 were recorded in the Greater So-chi, Krasnaya Polyana areas, in Kabardino-Balkaria, and in the adjacent territory of Georgia in the area of Kazbek volcano. The area of manifestation of earthquakes with intermediate hypocenter depths, which previously belonged only to the Terek-Caspian trough (the territory of the Chechen Republic) along the diagonal Benoy-Eldarov suture zone, expanded in 2013 to the southeast and advanced under the structures of the Dagestan wedge. According to the level of seismic energy released, seismicity of the territory of the North Caucasus in 2013 characterized in accordance with the scale of the seismicity level as “background low” for the period of observations from 1962 to 2013. The strongest earthquakes occur in the connection zones of the main tectonic structures.

ИССЛЕДОВАНИЕ СЕЙСМОСТОЙКОСТИ ГРУНТОВЫХ ПЛОТИН ОТ ДЕЙСТВИЯ МНОГОКРАТНЫХ СЕЙСМИЧЕСКИХ ВОЗДЕЙСТВИЙ, СООРУЖЕННЫХ В ГОРНО- СКЛАДЧАТЫХ РЕГИОНАХ

The problem of seismic stability of homogeneous earth dams constructed in complex geohydrodynamic regions has been solved. The calculations are performed using from the finite element method. Given the great extent at the base of such dams, the general equation of their motion is solved taking into account the well-known “traveling wave” method. It is shown that the offset of the existing viscous-plastic properties of earth dams already under the influence of a one-time strong seismic impact in them residual deformations arise, which subsequently develops even with weak earthquakes. This circumstance must be taken into account when designing such dams.