In 2017, the strongest earthquakes over the past two decades occurred in the central and southeastern Kopetdag – on April 5 with KR=14.3, MwGCMT=6.0 and on May 13 with KR=13.4, MwGCMT=5.7. The April 5 earthquake was also the strongest during the entire seismic history of a zone with a radius of 45 km from the epicenter. Both events were felt in the settlements of Iran, Turkmenistan, Afghanistan and other countries. The maximum shaking intensity was recorded in the nearest settlements of Iran – I=6 in the city of Torbet Jam during the earthquake on April 5 and I=7 in the city of Bojnurd during the event on May 13. For the earthquake of April 5, located in the contact zone of the southeastern Kopetdag with Binalud mountains, an isoseist map is constructed, on the basis of which the northwestern orientation of the isoseists are determined, coinciding with the strike of the nearest faults, of the aftershock cloud and of one of the nodal planes of the focal mechanism. At the same time, a southwest dip of the aftershock cloud is found, which does not correspond to the northeast dip of the nodal plane chosen as the active one. This discrepancy apparently indicates the complex structure of the fault zone, with areas of dip in different directions or with two parallel faults, which planes are dipping to the northeast and southwest. For the earthquake of May 13, 2017 in the central Kopetdag, which was preceded by a three-month seismic calm, the calm zone boundaries are defined, the spatial and temporal features of the aftershock process are studied. According to the determined equation of macroseismic effect propagation, the intensity at the epicenter of the May 13, 2017 earthquake is obtained – I0=7–8. This estimate is confirmed by the 7-point shaking intensity in Bojnurd (=24 km).
Аннотация. В 2013 г. мониторинг сейсмических процессов в Копетдагском регионе осуществлялся стационарной сетью 19 аналоговых и двух цифровых станций, поддерживаемой 11 передвижными цифровыми станциями. С сентября по декабрь на восьми аналоговых станциях-«Даната», «Красноводск», «Небитдаг», «Кенекесир», «Кара-Кала», «Гаурдак», «Серный» и «Серахс»-были установлены цифровые комплекты типа GEOSIG с перспективой дальнейшей замены ими аналоговой аппаратуры. Всего за год зарегистрировано 158 землетрясений с К Р ≥8.6, для 41 события определены механизмы очагов. В 2013 г. на территории региона снизилась как выделившаяся сейсмическая энергия (ΣE=7.0510 12 Дж, по сравнению с ΣE=17.62•10 12 Дж в 2012 г.), так и сейсмическая активность (А 10 =0.032 по сравнению с А 10 =0.038 в 2012 г.), однако в отдельных районах (Балхано-Каспийский, северная часть Туркмено-Хорасанского района) сейсмическая активность, наоборот, повысилась. Особенно заметна активизация сейсмичности в районе г. Магтымгулы, где она началась в 2012 г. в виде роев землетрясений с нарастающей суммарной энергией, а 9 декабря 2013 г. проявилась землетрясением с К Р =12.4 с большим количеством афтершоков. Цепочка афтершоков выстроилась в северовосточном направлении от эпицентра главного толчка, отмечая западную границу активизировавшегося в 2012-2013 гг. блока земной коры, а субширотный отрезок прямой, проходящей через эпицентры главного толчка, афтершока 10 декабря, предваряющего события 28 августа и заканчивающейся местоположением роя № 1 в 2012 г., определил его южную границу. Такое предположение о конфигурации мобильного блока земной коры поддерживает северо-восточная и субширотная ориентация плоскостей разрывов в очагах большинства землетрясений 2012-2013 гг. в этом районе, а присутствие как взбросовых, так и сбросовых компонент подвижек в очагах указывает на знакопеременный характер движений на границах блока.
In 2014, seismic monitoring in the Kopetdag region was carried out by a network of 29 seismic stations (20 stationary and nine mobile stations) of the State Seismological Service of the Academy of Sciences of Turkmenistan (SSS ANT), which in April became part of the newly formed Institute of Seismology and Atmo-spheric Physics, ANT. In total, 225 earthquakes with KP≥8.6 were recorded during the year, and focal mechanisms for 24 events were determined. Seismic process intensification continued around the town of Magtymguly. This began in April 2012 with earthquake swarm and continued in 2012–2014 with a series of earthquakes along the borders of the mobile blocks of the earth’s crust in the north of the Iranian plate, at the zone of its contact with Eurasia. On February 13 the strongest earthquake in Turkmenistan in 2014 with KP=12.8 occurred. It was located near the place of the April 2012 swarm. In June 2014 a seriesof more than of more than 2000 earthquakes with KP=4–10 was recorded 60 km east of this earthquake. This indicates a continued seismic activity and the possibility of strong earthquakes here. In the Kopetdag region as a whole, the seismic activity A10 and the seismic energy E released for 2014 reached the background level, after lowering of these parameters noted over the past several years compared to the average annual values for the period 1993–2013.
In 2016–2017, seismic monitoring in the Kopetdag region was carried out by a network of 34 seismic stations of the Institute of Seismology and Atmospheric Physics of the Academy of Sciences of Turkmenistan. This network included 20 stationary and 14 mobile stations. Within just 2 years, 651 earthquakes with KR≥8.6 have been registered, of which 41 were tangible. Focal mechanisms were determined for 83 seismic events. In Turkmenistan, the strongest and most felt earthquakes occurred in the Balkhan-Caspian region: on October 26, 2016 with KR=12.9 (Mw=5.5) and on February 5, 2017 with KR=12.4 (Mw=5.0). The first event was felt in Balkanabat city with intensity of 4–5, the second – in Kumdag settlement with intensity of 4. Among the earthquakes outside of Turkmenistan, the events of the Turkmen-Khorasan area stand out with the highest magnitude and shaking intensity: April 5, 2017 with KR=14.3, Mw=6.0 and May 13, 2017 with KR=13.4, Mw=5.7. The first event was felt with intensity of I=6 in the Iranian city of Torbet Jam and with I=5 in several settlements. Among the seismoactive areas of the Kopetdag region, the largest amount of seismic energy in 2016 was released on the territory of the Balkhan-Caspian area, in 2017 – in the Turkmen-Khorasan area.
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.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.