THE MARCH 25, 2020 M_W=7.5 PARAMUSHIR EARTHQUAKE AND ITS IMPACT ON RECENT GEODYNAMICS OF THE ADJACENT SECTION OF THE KURIL-KAMCHATKA SUBDUCTION ZONE

An intraplate tsunamigenic earthquake with МW=7.5 occurred on March 25, 2020 southeast of the Paramushir Island (Kuril Islands) beneath the outer slope of the Kuril-Kamchatka Trench. Since 1900, this earthquake has been the largest event for an 800-km long oceanic slope and a 300-km long segment of the Kuril seismofocal zone located near the epicenter. Sub-horizontal compression stresses generated in the earthquake source region were oriented across the seismofocal zone. A type of motion is represented by reverse faulting along the both nodal planes.The compressive stress state in which there occurred the Paramushir earthquake reflects the present-day geodynamics in the subduction zone near the hypocenter. The paper shows that the earthquake occurrence is due to a strong mechanical contact surface between the Pacific and North American lithospheric plates in the subduction zone. The analysis of coseismic displacement of the nearest Global Navigation Satellite System (GNSS) station served as confirmation of the determination of fault plane solution of the earthquake. A seismogenerating motion occurred along the plane oriented to the southwest and dipping towards the trench. For Finite fault source models, there were calculated the increments of the Coulomb stress in the subduction zone. For the main fault plane, the increment of the Coulomb stress in the interpolate contact area propagates to a depth of ~30 km and reaches 1 bar.Coseismic stress increment in the subduction zone at the northern flank of the Kuril island arc, which has a high seismic potential at the present stage of the tectonic cycle, increases the likelihood of the largest interplate earthquake occurrence therein

МОДЕЛЬ ОЧАГА НЕФТЕГОРСКОГО ЗЕМЛЕТРЯСЕНИЯ 1995 ГОДА (СЕВЕРНЫЙ САХАЛИН) НА ОСНОВЕ ГЕОДЕЗИЧЕСКИХ ДАННЫХ

The May 27, 1995 Mw=7.0 Neftegorsk earthquake occurred in the north of Sakhalin Island, rupturing the Upper Piltun fault, a secondary feature of the main Hokkaido-Sakhalin regional fault zone. The fault geometry, coseismic slip model, and Coulomb stress changes in the earthquake focal area were calculated based on a finite fault modeling. We used near-field coseismic offsets at 24 points obtained by comparison between predating triangulation and GPS observations, which were collected before and after the earthquake. Our slip distribution model shows two major slip patches. Larger slip asperity (amplitude up to 6.36 m) was characterized by right-lateral strike-slip movements, which correspond to focal mechanism of the earthquake, whereas the northern segment has reverse fault mechanism with maximum slip of 2.64 m. The fault length and width, average slip and stress drop values are estimated at 78 km, 28 km, 1.91 m and 11.3 MPa, respectively. The estimated release moment is approximately 7.49×1019 N∙m equal to Mw=7.2, which is larger than that reported by the USGS and GCMT but consistent with the values reported by other researchers. The coseismic Coulomb stress changes enhanced the stress by more than 10 MPa on the southern segment of the Gyrgylaninsky fault and middle section of the Hokkaido–Sakhalin fault. Seismic risks on the nearest faults cannot be ignored in the future despite the fact that the earthquake with a magnitude of 5.8 occurred in 2010 near the Gyrgylaninsky fault. The recent GPS rates in the surroundings of the Neftegorsk surface rupture mean that the recurrence interval for similar earthquakes may be more than a thousand years.27 мая 1995 года на севере острова Сахалин произошло землетрясение Mw=7.0, в результате которого вскрылся Верхнепильтунский сейсморазрыв – вторичный сегмент главной Хоккайдо-Сахалинской разломной зоны региона. Геометрия сейсморазрыва, косейсмические смещения и изменение кулоновских напряжений в очаговой области рассчитаны на основе модели конечного источника. Для моделирования использовались косейсмические смещения 24 пунктов, которые получены путем сравнения данных триангуляции и GPS-наблюдений до и после землетрясения. Моделированием установлены два основных участка разрывных нарушений с различным распределением смещений. Больший участок (с амплитудой 6.36 м) характеризуется правосторонними сдвиговыми смещениями, направление которых соответствует механизму очага землетрясения, в то время как северный сегмент сейсморазрыва имел противоположную подвижку с локальной амплитудой смещения 2.64 м. Длина и ширина разлома, средние значения смещений и сброшенных напряжений составили 78 км, 28 км, 1.91 м и 11.3 МПа соответственно. Расчетный сейсмический момент 7.49×1019 Н·м соответствует магнитуде Мw=7.2 и несколько больше оценок USGS и GCMT, однако согласуется с данными других исследований. Косейсмическое приращение кулоновского напряжения более чем на 10 МПа выявлено в южном сегменте Гыргыланьинского и центральной части Хоккайдо-Сахалинского разлома. Несмотря на то, что на Гыргыланьинском разломе в 2010 г. произошло землетрясение магнитудой 5.8, сейсмическую опасность в районе исследований нельзя игнорировать в будущем. Величины современных скоростей GPS-пунктов в окрестности Нефтегорского сейсморазрыва свидетельствуют о том, что период повторяемости подобных землетрясений может составлять более тысячи лет

Group analysis and exact solutions of a class of variable coefficient nonlinear telegraph equations

A complete group classification of a class of variable coefficient (1+1)-dimensional telegraph equations $f(x)u_{tt}=(H(u)u_x)_x+K(u)u_x$, is given, by using a compatibility method and additional equivalence transformations. A number of new interesting nonlinear invariant models which have non-trivial invariance algebras are obtained. Furthermore, the possible additional equivalence transformations between equations from the class under consideration are investigated. Exact solutions of special forms of these equations are also constructed via classical Lie method and generalized conditional transformations. Local conservation laws with characteristics of order 0 of the class under consideration are classified with respect to the group of equivalence transformations.Comment: 23 page

ПАРАМУШИРСКОЕ ЗЕМЛЕТРЯСЕНИЕ 25.03.2020 г., М W =7.5, И ЕГО ВЛИЯНИЕ НА СОВРЕМЕННУЮ ГЕОДИНАМИКУ ПРИЛЕГАЮЩЕГО УЧАСТКА КУРИЛО-КАМЧАТСКОЙ ЗОНЫ СУБДУКЦИИ

An intraplate tsunamigenic earthquake with МW=7.5 occurred on March 25, 2020 southeast of the Paramushir Island (Kuril Islands) beneath the outer slope of the Kuril-Kamchatka Trench. Since 1900, this earthquake has been the largest event for an 800-km long oceanic slope and a 300-km long segment of the Kuril seismofocal zone located near the epicenter. Sub-horizontal compression stresses generated in the earthquake source region were oriented across the seismofocal zone. A type of motion is represented by reverse faulting along the both nodal planes.The compressive stress state in which there occurred the Paramushir earthquake reflects the present-day geodynamics in the subduction zone near the hypocenter. The paper shows that the earthquake occurrence is due to a strong mechanical contact surface between the Pacific and North American lithospheric plates in the subduction zone. The analysis of coseismic displacement of the nearest Global Navigation Satellite System (GNSS) station served as confirmation of the determination of fault plane solution of the earthquake. A seismogenerating motion occurred along the plane oriented to the southwest and dipping towards the trench. For Finite fault source models, there were calculated the increments of the Coulomb stress in the subduction zone. For the main fault plane, the increment of the Coulomb stress in the interpolate contact area propagates to a depth of ~30 km and reaches 1 bar.Coseismic stress increment in the subduction zone at the northern flank of the Kuril island arc, which has a high seismic potential at the present stage of the tectonic cycle, increases the likelihood of the largest interplate earthquake occurrence therein.25 марта 2020 г. юго-восточнее о. Парамушир (Северные Курильские острова) под внешним тихоокеанским склоном Курило-Камчатского глубоководного желоба произошло внутриплитовое цунамигенное землетрясение с магнитудой МW=7.5. Землетрясение оказалось сильнейшим с 1900 г. сейсмическим событием для прилегающих к эпицентру океанического склона протяженностью около 800 км и трехсоткилометрового сегмента Курильской сейсмофокальной зоны. В очаге землетрясения реализовались напряжения субгоризонтального сжатия, ориентированные вкрест сейсмофокальной зоны. Тип подвижки – взброс по обеим нодальным плоскостям.Напряженное состояние сжатия, в условиях которого произошло Парамуширское землетрясение, отражает современную геодинамическую обстановку в прилегающей к гипоцентру зоне субдукции. В работе показано, что возникновение землетрясения обусловлено высокой степенью сцепления поверхности механического контакта Тихоокеанской и Североамериканской литосферных плит в зоне субдукции. На основе анализа косейсмического смещения ближайшей Global Navigation Satellite System (GNSS) станции подтвержден выбор действующей плоскости сейсморазрыва в очаге землетрясения. Сейсмогенерирующая подвижка произошла по плоскости, ориентированной в юго-западном направлении и падающей в сторону глубоководного желоба. Для дислокационных моделей очага Finite fault рассчитаны приращения кулоновского напряжения в зоне субдукции. Для приоритетной плоскости сейсморазрыва приращение кулоновского напряжения в области межплитового контакта распространяется до глубины ~30 км и достигает 1 бара.Косейсмическое приращение напряжений в зоне субдукции на северном фланге Курильской островной дуги, который на современном этапе тектонического цикла обладает высоким нереализованным сейсмическим потенциалом, в долгосрочной перспективе повышает вероятность возникновения здесь сильнейшего межплитового землетрясения

ДЕФОРМАЦИИ ЗЕМНОЙ ПОВЕРХНОСТИ ОСТРОВА САХАЛИН ПО ДАННЫМ GPS‐НАБЛЮДЕНИЙ

The earth surface deformation was modeled for the North, Central and South Sakhalin on the basis of de‐ formation velocities recorded by the GPS stations of the Sakhalin Geodynamical Network. A pattern of contemporary horizontal deformation is intricate in the vicinity of the main submeridional faults of the island. On the island surface, the dominant deformation regime is compression; however, the spatial distribution of deformation is heterogeneous. The horizontal compression is mainly sublatitudinal and SW‐NE‐trending. In addition to compression, there are zones of rather intense right‐lateral strike‐slip in the northern and central parts of the island, while stretching dominates in the south‐eastern parts. The regional geodynamic setting is reflected in the seismicity of the island. Recently, the seismic activity has been increased in the areas characterized by intensive surface deformation, while the areas of low deformation rates correlate with the zones of weak and sparse seismicity.На основе GPS‐скоростей пунктов Сахалинской геодинамической сети выполнено моделирование деформированного состояния земной поверхности северной, центральной и южной части о. Сахалин. Полученные данные показывают сложную картину современных горизонтальных деформаций в окрестностях главных субмеридиональных разломов острова. Преобладающим деформационным режимом является сжатие островной суши, однако пространственное распределение деформаций неоднородно. Сокращение земной коры происходит в основном в субширотном и ЮЗ‐СВ направлениях. Наряду со сжатием на севере и в центре острова выделяются области достаточно интенсивных деформаций правостороннего сдвига, в юго‐восточной части острова преобладают деформации растяжения. Региональная геодинамическая обстановка находит отражение в сейсмичности острова. В районах интенсивного деформирования земной поверхности проявляется повышенная сейсмическая активность последних лет, тогда как области низких скоростей деформаций коррелируют с зонами слабой и разреженной сейсмичности

СОВРЕМЕННАЯ ГЕОДИНАМИКА ГАРОМАЙСКОГО АКТИВНОГО РАЗЛОМА (ОСТРОВ САХАЛИН)

In the northern Sakhalin Island, the tectonic activity of the fault zones is a potential threat to the industrial infrastructure of the petroleum fields. Recently, the background seismicity has increased at the Hokkaido‐Sakhalin fault that consists of several segments, including the Garomai active fault. In the studies of the regional deformation processes, it is important not only to analyze the seismic activity, but also to quantitatively assess the dynamics of deformation accumulation in the fault zones. In order to study the contemporary geodynamics of the Garomai fault, a local GPS/GLONASS network has been established in the area wherein trunk oil and gas pipelines are installed across the fault zone. Based on the annual periodic measurements taken in 2006–2016, we study the features of surface deformation and calculate the rates of displacements caused by the tectonic activity in the fault zone. During the survey period, no significant displacement of the fault wings was revealed. In the immediate vicinity of the fault zone, multidirectional horizontal displacements occur at a rate up to 1.6 mm/yr, and uplifting of the ground surface takes place at a rate of 3.4 mm/yr. This pattern of displacements is a reflection of local deformation processes in the fault zone. At the western wing of the fault, a maximum deformation rate amounts to 1110–6 per year. The fault is a boundary mark of a transition from lower deformation rates at the eastern wing to higher ones at the west wing. In contrast to the general regional compression setting that is typical of the northern Sakhalin Island, extension is currently dominant in the Garomai fault zone. The estimated rates of relative deformation in the vicinity of the Garomai fault give grounds to classify it as ‘hazardous’.Тектоническая активность разломных зон севера о. Сахалин представляет опасность для промышленной инфраструктуры разрабатываемых месторождений углеводородов. Повышенным уровнем фоновой сейсмичности в последние годы характеризуется Хоккайдо‐Сахалинский разлом, одним из сегментов которого является Гаромайский активный разлом. При исследовании проявлений региональных деформаци‐ онных процессов важен не только анализ сейсмической активности, но и количественная оценка динамики накопления деформаций в разломных зонах. Для изучения современной геодинамики Гаромайского разлома в районе его пересечения магистральными нефтегазопроводами создана локальная сеть GPS/ГЛОНАСС наблюдений. Ежегодные периодические измерения 2006–2016 гг. позволили установить характер деформи‐ рования земной поверхности и получить количественные оценки скоростей смещений, вызванных тектонической активностью разломной зоны. За период наблюдений значимых смещений крыльев разлома не выявлено. В ближайших окрестностях разломной зоны наблюдаются разнонаправленные горизонтальные смещения со скоростью до 1.6 мм/год и поднятие в виде изгиба земной поверхности со скоростью 3.4 мм/год. Такая картина смещений является отражением локальных деформационных процессов в зоне разлома. Максимальные скорости деформаций 1110–6 в год приурочены к западному крылу разлома. Разлом разграничивает переход от пониженных скоростей деформаций на восточном крыле к более высоким на западном. В отличие от общей региональной обстановки сжатия, характерной для севера о. Сахалин, зона Гаромайского разлома в настоящее время находится в преобладающих условиях растяжения. Выявленные скорости относительных деформаций в окрестности разлома позволяют отнести его к категории «опасные»

Peculiarities of Epidemiological Situation on Crimean Hemorrhagic Fever in the Russian Federation at the Current stage

Objective. The analysis of epidemiological situation on Crimean hemorrhagic fever (CHF) in the Russian Federation at the current stage, identification of ways to improve the epidemiological surveillance and prophylaxis of the disease. Materials and methods. Data from statistical documentation and results of annual epizootiological monitoring of the CHF natural focus provided by the Administrations of the Rospotrebnadzor, Centers of Hygiene and Epidemiology in entities of the Southern and the North-Caucasian Federal Districts, Reference Centre for CHF monitoring, Research Anti-Plague Institutions and Plague Control stations were used for work. Results and conclusions. The CHF epidemio­logical situation remains unstable, the cases of the disease (including fatal) are registered every year. High activity of the CHF natural focus persists. The northward expansion of CHF natural focus boundaries is observed. The main causes of the unfavorable CHF epidemiological situation are associated with increase in the numbers and period of activity of ticks Hyalomma marginatum due to favorable climatic conditions. The list of priority measures to stabilize the CHF epidemiological situation developed by the Rospotrebnadzor has resulted in decrease in CHF cases by 51.9 % in 2017 compared to 2016 across all the territory of the south of the Russian Federation. The CHF morbidity in 2018 was 1.5 times lower than the average multi-year values (72 CHF patients). The number of CHF cases in comparison to 2017 has decreased by 1.3 times in the Stavropol Territory and by 1.4 times in the Rostov Region. The CHF morbidity has increased in the Astrakhan Region (by 3 times) and Volgograd Region (by 2.3 times). Nosocomial CCHF virus infections cases associated with non-compliance to anti-epidemic regime in hospitals while providing treatment of CHF patients were registered in 2011 (in the Rostov Region) and in 2016 (in the Stavropol Territory). This highlights the need to improve the training of health-care staff for admission of patients with this particularly dangerous infection

Epidemiological situation on Crimean-Congo Hemorrhagic Fever in the Russian Federation in 2021

The review presents an analysis of the epidemiological and epizootiological situation on Crimean-Congo hemorrhagic fever (CCHF) in the Russian Federation in 2021. 49 cases of CCHF were detected in 2021, which is 1.53 times higher than in 2020. The mortality rate was 6.1 %. Sporadic cases of CCHF were registered in the Stavropol Territory, Rostov, Volgograd Regions, the Republics of Dagestan and Kalmykia. The incidence rates of CCHF were below the long-term average annual values in the majority of the constituent entities. Epizootiological survey of stationary observation points has revealed that the number of Hyalomma marginatum imago corresponded to the average long-term indicators in 2021, the peak of H. marginatum activity was noted in the II–III decades of May. The proportion of Ixodidae tick pools positive for Crimean-Congo hemorrhagic fever (CCHF) virus markers exceeded the long-term average indexes in a number of regions. On the territory of the natural focus of CCHF, the circulation of the CCHF virus of the genetic lineages “Europe-1” and “Europe-3” was detected in 2021. Based on the analysis of the epidemiological data of the previous year and natural and climatic factors affecting the abundance and vital activity of H. marginatum ticks, risk-based quantitative forecast for the incidence of CCHF in the Stavropol Territory for 2022 has been compiled

Natural Focal Viral Fevers in the South of the European Part of Russia. Hemorrhagic Fever with Renal syndrome

Objective of the study was to determine the modem epizootic and epidemic peculiarities of hemorrhagic fever with renal syndrome in the south of the European part of Russia. Materials and methods. Data of statistical documentation (epidemiological survey of the infectious disease focus, annual summary reports dated 2009-2018) and epizootic monitoring data submitted by the Rospotrebnadzor Administrations and the Centers of Hygiene and Epidemiology in the constituent entities of the Southern and the North Caucasian Federal Districts were used. Descriptive, analytical methods and retrospective epidemiological analysis were applied. Results and discussion. The circulation of hantavirus in the Volgograd and Astrakhan Regions, Stavropol and Krasnodar Territories, Republics of Adygeya, Kalmykia and Crimea was confirmed. However, two geographically and genetically isolated groups of hantaviruses circulating in the Volgograd Region and in the mountain-foothill zone of the Krasnodar Territory and the Republic of Adygeya were the most epidemiologically significant. Over the period of 2009-2018, 152 HFRS cases with annual fluctuations from 4 to 25 cases were registered. Almost all patients lived in the Volgograd Region (44 cases), where the incidence is caused by the HFRS-Puumala virus, or in the Krasnodar Territory (98 cases), where the HFRS Hantavirus Dobrava-Ap circulates. In HFRS patients with the HFRS-Dobrava-Ap virus severe clinical forms were noted at twice the rate, a fatal outcome in one patient with HFRS-Puumala was recorded. The correct preliminary diagnosis was made for 56.3 per cent of patients in the Volgograd Region and only for 31.7 per cent of patients in the Krasnodar Territory and in the Republic of Adygeya. There are different types of natural HFRS foci in the European south of Russia, they vary by the type of hosts and hantaviruses circulating in them - Puumala, Dobrava, Tula, and Dobrava-Ap. Natural foci where of HFRS-PUU and HFRS-DOB-Ap viruses circulate have high epidemic potential. Severe forms of the HFRS are more often observed in patients with the HFRS-DOB-Ap virus