SEISMICITY of the ARCTIC in 2015

The article provides an overview and analysis of seismicity within the boundaries of the Arctic region for 2015, a description of seismic station networks, and processing methods. The catalog of earthquakes in the Arctic region was compiled on the basis of catalogs of several organizations and seismological centers. In total, 334 earthquakes are included in the earthquake catalog. Most of the earthquakes that occurred in 2015, including all the strongest earthquakes, were located within the mid-ocean ridges of Mon, Knipovich and Gakkel. In the offshore territories, most of the earthquakes were confined to the Svalbard archipelago, in particular, to the seismically active zone in the Sturfjord strait. The renewal of instrumental seismological observations in 2011 (station ZFI) on Alexandra Land Island in the Franz Josef Land archipelago made it possible to record weak earthquakes in the north of the shelf of the Barents and Kara Seas. For twelve earthquakes, the focal mechanism parameters are presented according to the Global CMT catalog.

TERESVA-II EARTHQUAKE on July 19, 2015 with KR=11.1, МSH=3.4, I0=6 (Transcarpathia, Ukraine)

The instrumental and macroseismic data of the Teresvа-II earthquake on July 19, 2015 with the energy class KR=11.1, МSH=3.4 are considered. The earthquake occurred in the seismically active Tyachevo-Sigetskaya zone of Transcarpathia in the upper part of the Earth's crust and caused shaking intensity of I0=6 in the epicentral zone near the village of Teresva. The data on the focal mechanism solution, intensity distribution, parameters of the strongest aftershocks are presented. The release of seismic energy continued for 35 days. During this time, 306 earthquakes were recorded in a wide energy range. The space-time and energy properties of the complex sequence of the Teresvа earthquakes in 2015 have been investigated. The tectonics and previous seismi-city of the area are described.

SEISMICITY of the RUSSIAN PART of EAST EUROPEAN PLATFORM and ADJACENT TERRITORIES in 2015

It is reported that 41 stationary seismic stations, 2 arrays, and 7 temporary seismic stations, located in the area of Novovoronezh and Kursk nuclear stations, monitored seismicity of the Russian territory of the East European Platform (EEP) in 2015. The registration capabilities of the seismic network at the EEP as a whole were estimated based on the average station noise level and the equation for the energy decay of seismic phases. Zones with the best capabilities have been allocated. A feature of seismicity in 2015 is the manifestation of earthquakes of moderate magnitudes (ML=2.7–3.9) in the peripheral regions (in the southwest, west, and northwest) and in zones associated with paleorift structures: in the southwest – with the Dnieper Donetsk and in the northeast – with the Kirov-Kazhim and Soligalich (Central Russian) aulacogenes. The results of the macroseismic survey are given for the earthquake in Poltava on February 2, 2015, with M=3.7; focal mechanisms of two earthquakes (03.02.2015 and 12.06.2015) are constructed. According to the data of the Latvian Center, an earthquake was recorded in the region of Lithuania bordering the Kaliningrad region. Weaker natural seismicity with ML≤2.5 was recorded in Karelia and the regions bordering with Finland, near the Kandalaksha Bay, near the Khibiny, and Lovozersky massifs on the Kola Peninsula, and on the territory of the Voronezh crystalline massif.

MIDDLE URAL EARTHQUAKE on October 18, 2015, ML=4.7, I0=6

Instrumental and macroseismic data on the earthquake of 18.10.2015 at 21h44m UTC, ML=4.7, I0=6 in the Sverdlovsk region, near the village of Sabik (Middle Urals) are presented. A significant amount of macroseismic data made it possible to build a map of the macroseismic field, taking into account the anisotropic nature of the propagation of the seismic effect. Taking into account the decision of the focal mechanism, the tectonic position of the source was substantiated.

SEISMICITY of NORTHERN EURASIA in 2015

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).

SEISMISITY of THE VOLCANIC AREAS of KAMCHATKA in 2015

The results of near real-time monitoring of the active Kamchatka volcanoes are described. Continuous monitoring was carried out using three remote methods: 1) seismic monitoring according to automatic telemetric seismic stations; 2) visual and video observation; 3) satellite observation of the thermal anomalies and the ash clouds. Annual results of seismic activity of the Northern (Shiveluch, Kluchevskoy, Bezymianny, Krestovsky, and Ushkovsky), the Avacha (Avachinsky, and Koryaksky), the Mutnovsky-Gorely volcano groups and the Kizimen volcano are presented. 5464 earthquakes with КS=1.8–8.1 were located for the Northern volcano group, 302 earthquakes with КS=1.7–5.7 – for the Avacha volcano group, 295 earthquakes with КS=2.1–6.8 for the Mutnovsky-Gorely volcano group, 462 earthquakes with КS=2.2–8.3 for Kizimen volcano, and 165 earthquakes with КS=2.5–8.4 for Zhupanovsky volcano in 2015. Maps of epicenters, quantities of seismic energy and earthquake distribution by energy classes are given. All periods of activity were fixed and investigated by remote methods in 2015: intensive volcanic activity of the Sheveluch volcano associated with a new cone; the summit explosive-effusive eruption of the Kluchevskoy volcano in January–April; and a continuation of seismic and volcanic activity of the Zhupanovsky volcano after 56-year quite period.

SEISMICITY of KAMCHATKA and COMMANDER ISLANDS in 2015

The seismicity review of Kamchatka and surrounding territories for 2015 is given. In the Kamchatka earthquake catalogue, the minimum local magnitude of completeness is MLmin=3.5, and for earthquakes with h≥350 km under the Okhotsk sea MLmin=3.6. The Kamchatka earthquake catalogue for 2015 with ML3.5, published in the Appendix to this issue, includes 1213 events. 92 earthquakes of the catalogue with ML=3.0–6.5 were felt in Kamchatka and surrounding areas with seismic intensity I=2–6 according to the MSK-64 scale. For all events with ML5.0 that occurred in 2015 in the KB GS RAS area of responsibility, an attempt to calculate the seismic moment tensor (SMT) was made. There are 32 such events in the regional catalogue. For 28 earthquakes the SMT and depth h of the equivalent point source were calculated successfully. The calculations were performed for the SMT double-couple model using a nonlinear algorithm. In 2015, a typical location of the earthquake epicenters was observed in the Kamchatka zone. In 2015, the seismicity level in all selected zones and in the region as a whole correspond to the background one according to the “SESL’09” scale. The number of recorded events with ML3.5 and strong earthquakes with ML5.0 is close to the average annual value. Anomalous and significant events were not recorded.

SOURCE PARAMETERS of STRONG EARTHQUAKES OCCURRED in the BAIKAL REGION and TRANSBAIKALIA in 2015

We calculated seismic moment tensors in a double-couple approximation (focal mechanisms, scalar seismic moments, and moment magnitudes) and hypocentral depths for twenty earthquakes with Mw≥4.2 that occurred in the Baikal region and Transbaikalia in 2015. The initial data were amplitude spectra of Rayleigh and Love waves obtained from their records at the broadband seismic stations of the IRIS and the DK networks and first-motion polarities of body waves recorded at regional distances. A combination of the normal fault and strike-slip movements dominate in the sources of the major part of the study earthquakes. For the strongest of the considered seismic events (Mw≥4.6), the subvertical compression and subhorizontal tension in the SE-NW direction prevail, i.e. the tension is perpendicular to the main structures of the Baikal rift zone. The seismic events with Mw<4.6 are characterized by a more scattered orientation of compression and tension axis that could be caused, for instance, by stress redistribution in small-scale crustal blocks after stronger earthquakes. The obtained results are of great value for issues concerned with seismic hazard assessment and the development of geodynamical models of the lithosphere evolution of the study region.

SEISMICITY of the URALS and WESTERN SIBERIA in 2015

The article summarizes information about seismic network in the Urals and Western Siberia region, describes processing technique, presents a short analysis of the seismic activity in 2015. Seismic network capability is shown for the whole territory under control. It was found that about 82 % of registered events are explosions in mines and open pits, 37 events are natural or induced ones. For the strongest induced events, variants of source parameters obtained by different agencies are shown. The strongest tectonic event in 2015 and for the last century (after 1914) is the Middle Ural earthquake with ML=4.7, I0=6 that occurred on October 18, 2015.

SEISMICITY of TAJIKISTAN and ADJACENT TERRITORIES in 2015

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=1.8151017 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 14106 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.