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.
Аннотация. Каталог землетрясений Таджикистана за 2013 г. содержит 4997 землетрясений с К Р =8.6-15.0, из них 3865-глубокофокусные Памиро-Гиндукушские землетрясения с h=70-250 км и 1132-мелкофокусные, разбросанные по всей территории. Суммарная сейсмическая энергия, выделившаяся в очагах всех землетрясений, составила Е=1.4610 15 Дж. Непосредственно в границах Республики с наибольшей интенсивностью I 0 =6 баллов (К Р =12.4, Mw=4.7) произошло землетрясение 10 ноября в Вахдатском районе, в 24 км юго-восточнее столицы Душанбе. Наиболее сильно пострадали три селения-70 % жилых домов этих селений стали непригодными для жилья. Максимальное среди глубоких землетрясений 2013 г. зарегистрировано в Афганской подзоне 4 апреля с К Р =14.0, Mw=5.4, h=250 км. Из-за большой глубины оно вызвало сотрясения небольшой (I3) интенсивности в эпицентральной зоне и ощущалось в Таджикистане, Афганистане и Пакистане. Однако в целом сейсмический процесс в Республике протекал в фоновом режиме. Ключевые слова: сейсмичность территории Таджикистана, сейсмическая сеть, каталог землетрясений.
The seismic monitoring system consisting of seven digital stations continued to operate in Tajikistan in 2015. This network has registered 9071 earthquakes with KR=8.6–17.0, 6427 of which were Pamir-Hindu Kush earthquakes with intermediate depths (h=70–300 km), and 2644 were shallow events. The total seismic energy released was E=1.8151017 J. The strongest for 2015 was the Hindu Kush earthquake on Octo-ber 26 with Mw=7.5, h=230 km (hpP=217 km) that occurred near the southern borders of the Republic. This earthquake caused significant damage and the death of at least 115 people. It was felt on the territory of 14 states, with a total shaking area of more than 14106 km2. A detailed isoseismal map of this earthquake is given for the Tajikistan territory only. The earthquake was accompanied by a series of over 1400 aftershocks with KR=8.6–12.8, unexpectedly numerous for a deep earthquake. Within the borders of the Republic, the Sarez-II earthquake occurred near the Lake of Sarez on December 7 with Mw=7.2, h=20 km, I0=8, was the strongest one. Undoubtedly, it was triggered by the Hindu Kush earthquake on October 26. In total, more than 500 houses were damaged, dozens of people were injured, and there were human casualties. A detailed isoseismal map of this earthquake was made for four levels of intensity – I=7, 6, 5 and 4. The number of its aftershocks for 24 days only was 1342, with KR=8.6–13.9. As a result the level of seismicity in Tajikistan in 2015, both in terms of the number of earthquakes and the level of released seismic energy, was the highest during the period of instrumental observations.
On October 26, 2015, a strong Hindu Kush earthquake with KR=17.0, Mw=7.5 occurred in the Afghan Pamir-Hindu Kush subzone at a depth of hpP=217 km. Shakes of varying intensity caused by this earthquake were recorded in settlements of 14 states: Afghanistan, Tajikistan, Pakistan, Turkmenistan, India, Kyrgyzstan, Uzbekistan, Kazakhstan, China, Iran, Nepal, United Arab Emirates, Russia, Qatar and Bangladesh with a total area of S=14106 km2. The earthquake was preceded by three large (KR=12.5, 12.1, 14.0) foreshocks and was accompanied by a series of more than 1400 aftershocks unprecedented for aftershocks of deep earthquakes with KR=9–13. The energy step between the mainshock and the maximum foreshock is Kfor=3.0, between the mainshock and the maximum (KR=12.8) aftershock – Kaft=4.2. The aftershock recurrence graph has a slope =–0.67, which in absolute value is higher than the average value in the region =0.50. The attenuation para-meter of the Omori law in the initial phase of attenuation, =–1.26, in absolute value is also higher than the average =1.0 for strong earthquakes in the World. Based on the results of a joint analysis of the focal me-chanism solutions of different agencies and vertical sections along and across the aftershock cloud, it was con-cluded that an upthrust movement occurred in the source along a steep east-south-east nodal plane, dipping to the south. The reason for the activity at the site of the earthquake is the movement of the Indian continent to the north and its collision with Eurasia, as a result of which the separation and subduction of the Hindu Kush plate continue. The Hindu Kush earthquake on October 26, 2015, and its aftershocks are just one of the events of successive deformation and stress relief in the latitudinal zone, marked in 2015 by the migration of earthquake epicenters with KR=13–17 from east to west.
The results of analysis of instrumental and macroseismic data, focal mechanism, and seismotectonic position of the strong Gonam earthquake occurred on the Aldan Highlands are given. The manifestations of aftershock activity and its connection with the regional Tyrkanda fault are analyzed in more detail. This fault is confidently observed in the positive anomalies of the magnetic field. The geometric parameters (width and length) of the aftershock zone are given.
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