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).
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).
The review of the seismicity of Northern Eurasia in 2016–2017 contains a description of seismic networks, features of the seismic regime and individual significant earthquakes in 16 regions of Russia and neighboring countries. Seismic monitoring of this territory was carried out by networks of seismic stations in Russia, Azerbaijan, Armenia, Belarus, Kazakhstan, Kyrgyzstan, Latvia, Moldova, Turkmenistan, Tajikistan, Uzbekistan and Ukraine. In most regions, the seismic process proceeded in the "background" mode. In Northern Eurasia as a whole, a decrease in the seismic energy released in 2016 was noted relative to its long-term average value, which was also observed in 2015. The increase in the released energy in 2017 did not lead to reaching the level of 2015. The Near Aleutian earthquake on July 17, 2017 with Mw=7.8 was the maximum for the period under consideration. It was one of the strongest instrumentally recorded events in the western part of the Aleutian arc. The maximum shaking intensity in the territory of Northern Eurasia (I=7) was caused by two earthquakes – the Aketao earthquake on November 25, 2016 with Mw=6.6, localized in China, near its borders with Tajikistan and Kyrgyzstan, and the Karamyk earthquake on May 3, 2017 with Mw=6.0, Tajikistan. Seismic activity of platform territories is confirmed by the Mariupol earthquake on August 7, 2016 with Mw=4.6 and intensity I=5 in Mariupol.
The ML local magnitudes of the earthquakes of Armenia, Azerbaijan, the Arctic and the Baltic Shield (KOGSR and FCIAR station networks), the Urals and Altai and Sayan were analyzed. The regional dependences of ML on the mbISC “external” magnitude are established. It is shown that the magnitudes ML of weak and moderate seismic events registered by the seismic stations of these regions, with the exception of Altai and Sayan, are close at the same mbISC both among themselves and to ML according to the NAO, HEL, DDA, TEH networks of neighboring countries. For all regions, except for Altai and Sayan, a general dependence is established in the form: MLav=1.06⋅mbISC–0.34. A significant overestimation of the ML of Altai and Sayan earthquakes recorded by the regional network is found relative to other data. For the main group of data, the excess of local magnitudes ML=f(KR) over magnitude M in the known T.G. Rautian ratio, KR=lgE=1.8⋅M+4, by DM=0.2÷0.4 in the magnitude range of ML=1.0÷6.0 is shown. For Altai and Sayan earthquakes, the overestimation of local magnitudes is more significant and should be taken into account when calculating seismic energy using the regional ratio KR=f(ML). In general, magnitudes in the ratio KR=1.8⋅M+4 for weak and moderate earthquakes are closer to local magnitudes ML, and for strong events with KR>13 (Ms>5.0) – to surface wave magnitudes Ms.
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.