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.

On the initial velocity of the glacial-stone material movement, the air-blast, the nature of the carrier medium and the range of action of sudden explosion-like gas-dynamic surge of the Kolka glacier

Начальная массовая скорость компактного движения выброшенного ледово-каменного материала ледника Колка, достигнутая на стадии газового ускорения в эпицентральной зоне взрывоподобного внезапного газодинамического выброса ледника, составляла около 300 м/с. Именно столь высокие значения величины начальной массовой скорости выброса основного количества ледово-каменного материала определили возможность образования сопутствовавшей выбросу ударной воздушной волны, которая и на большом расстоянии от эпицентра выброса (порядка 15 км) все еще имела значительную интенсивность. Воздушным был характер несущей среды для всего Геналдонского лавинообразного потока в пределах выделенной прежде всего по этому признаку зоны транзита на всем многокилометровом ее протяжении, а для начальной и основной стадий выброса – и за пределами этой зоны (до Скалистого хребта). Дальность же действия взрывоподобного внезапного газодинамического выброса ледника Колка 20 сентября 2002 года, безусловно, не ограничивалась лишь вместилищем ледника Колка или Колкинским цирком, как иногда полагают, а захватывала огромную территорию Колкинского и Геналдонского ущелий и была ограничена (да и то не полностью) лишь непреодолимой механической преградой Скалистого хребта. Цель работы. В плане сопоставления с взрывоподобными направленными газодинамическими выбросами ледников рассматривается вопрос об истории изучения направленных вулканических взрывов, установленных полстолетием ранее. Методы работы. Проведен анализ имеющихся данных и существующих походов их оценок. Результаты работы. Показана огромная мощность взрывоподобных направленных газодинамических выбросов ледника Колка, вполне сопоставимых в данном отношении с крупными направленными вулканическими взрывами. The initial mass velocity of the compact movement of the ejected glacial-stone material of the Kolka glacier, reached at the stage of gas acceleration in the epicentral zone of the sudden explosion-like gas-dynamic surge of the glacier, was about 300 m/s. Exactly such high values of the initial mass velocity of the surge of the main amount of glacial-stone material that determined the possibility of the formation of an accompanying ejection of the air-blast, which had a significant intensity even at a great distance from the surge epicenter (about 15 km). The nature of the carrier medium for the entire Genaldon avalanche flow was aerial within the transit zone distinguished primarily according this character along its entire length of many kilometers; and for the initial and main stages of the surge the nature was the same outside this zone (up to the Skalisty (Rocky) Ridge). The range of action of the sudden explosion-like gas-dynamic surge of the Kolka glacier on September 20, 2002, was certainly not limited only by the reservoir of the Kolka glacier or the Kolka cirque, as it is sometimes supposed, but captured the vast territory of the Kolka and Genaldon gorges and was limited (and even then not completely) only by the insurmountable mechanical barrier of the Skalisty (Rocky Ridge). Aim. In terms of the comparison with explosion-like directional gas-dynamic surges of glaciers, the article considers an issue of the history of study of directional volcanic explosions determined half a century earlier. Methods. The analysis of the available data and the existing approaches for their assessments was carried out. Results. The results of the work show the enormous power of explosion-like directed gas-dynamic surges of the Kolka glacier, which are quite comparable in this respect with large directed volcanic explosions.

The Impact of High-Energy Mining-Induced Tremor in a Fault Zone on Damage to Buildings

Seismic energy propagation from the hypocentre of mining-induced tremors usually causes an uneven distribution of the peak ground velocity PGVHmax in tectonically complicated structures, and consequently, an uneven distribution of damage to buildings located on the ground surface. This study aimed to estimate the impact of high-energy mining-induced tremors in fault zones on damage to buildings. In the study, we describe a case of one of the highest-energy mining-induced tremors E = 4.0 · 108 J (local magnitude ML = 3.6) that occurred in the Upper Silesian Coal Basin (USCB), Poland. The hypocentre of the tremor was most probably located in the Barbara fault zone, one of the larger faults in that western part of the USCB. Numerous damaged buildings on the terrain surface were registered, both in the epicentral zone and at a greater distance from the epicentre, mostly from the southern side of the Barbara fault zone. We calculated that the tremor was characterised by a normal slip mechanism associated with the same kind of fault as the Barbara fault. The azimuth of the nodal planes was similar to the west-east direction, which is consistent with the azimuth of the Barbara fault. From the focal mechanism, the greatest propagation of seismic energy occurred in south and west-east directions from the tremor hypocentre towards the surface. It was found that from the northern side of the hanging wall of the Barbara fault, there were 14 instances of damage (19%), and in the southern part of a hanging wall, there were 58 (81%). Therefore, the directionality of seismic energy propagation is aligned with the focal mechanism acting in the Barbara fault. It has also been concluded that a width of the zone of up to about 1200 m along the Barbara fault is the most threatening on the basis of registered building damage in the geological conditions of USCB. The study has shown that in assessing the impact of mining-induced tremors on buildings and the environment, the disturbance of seismic energy propagation by larger faults should be considered.

Early Manifestations of Short-Term Precursors in Stress-Strain State Dynamics of Southern California

Abstract—The stress-strain state before the М = 7.1 Ridgecrest earthquake in Southern California is analyzed based on spatiotemporal distribution of shear strains calculated in the geomechanical model within local ~100 × 100 km crustal segments at a depth of 3–7 km. In the epicentral zone of the earthquake, starting from three years before the event, a successive series of the time intervals, up to the occurrence of the earthquake, when shear deformations are completely absent and rocks are farthest from ultimate strength—the so-called quiescence zones—are established. The spatial distribution of shear strains in the vicinity of the epicentral zone is analyzed during the quiescence intervals and subsequent bursts of maximum amplitude in the epicentral zone itself. The time intervals of the bursts are called excursions. The successive emergence of maxima in shear strain amplitudes in the epicentral zone and surrounding medium during the excursions corresponds to the situation of a swing when the entire preparation region of a future earthquake is rocking up to the moment of event. Consistency of the obtained results with the existing theoretical models of earthquake preparation is discussed.

KAJI-SAIEARTHQUAKEonNovember 14, 2014 withКР=13.7, Mw=5.4, I0=7 (Kyrgyzstan, SouthernIssyk-Kul’)

Information on the earthquake with Mw=5.4 that occurred on the southern coast of the Issyk-Kul lake on the southwestern slope of the Tegerek mountains (Kyrgyzstan) on November 14, 2014 is given. The epicenter is located in the Jumgalo-Terskey zone, identified as the Tonsky block, in which felt earthquakes with intensity up to 7 have occurred repeatedly. 231 aftershocks were recorded in the first day, in the second day – 13 aftershocks, then seismic activity decreased. Most of the aftershocks are localized in the depth range of 17–21 km, close to the depth of the main shock (h=20 km). The earthquake had the reverse fault type. Macroseismic survey was fulfilled only in the epicentral zone due to the complex weather conditions (late autumn, highlands). The theoretical isoseismal map was created for receiving the more complete picture of the earthquake impact outside of its epicentral zone.

EARTHQUAKE MAY 20, 2014, ML=2.8, I0=4–5 IN THE CENTRAL PART OF THE REPUBLIC OF BASHKORTOSTAN

The article provides macroseismic data on the earthquake 20.05.2014 18h26mUTC ML=2.8, that had a local but relatively strong macroseismic effect (I0=4–5) in the Chishminsky district of the Republic of Bashkortostan. After the event, macroseismic data were collected in 27 settlements in the epicentral zone. This data allowed to determine the macroseismic epicenter, which is close to the instrumental one. The events in the same area during the historical period were considered in detail and modern seismic records were revised. The data allowed to identify a series of similar seismic events with less magnitudes in 2014. The classification of these activities into two groups has been justified there. There are tectonic and natural events induced by Alkinskoye oil deposit exploration.

THE EARTHQUAKE IN DZHEYRAKH REGION OF THE REPUBLIC OF INGUSHETIA ON MAY 24, 2020.

В настоящей статье приводится краткий анализ землетрясения с КР = 10.6, произо- шедшего 24 мая 2020 года на территории Джейрахского района Республики Ингушетия в 12h33m по Гринвичу с интенсивностью сотрясений в эпицентре 4 балла. Представлены инструментальные данные об очаге и макросейсмические проявления события. Описаны волновая картина сейсмиче- ского сигнала и историческая сейсмичность, рассчитан механизм очага, рассмотрена тектониче- ская позиция эпицентральной зоны. .This article provides a brief analysis of an earthquake with KP = 10.6 that occurred on May 24, 2020 in Dzheyrakh region of the Republic of Ingushetia at 12h33m GMT with 4 points of earthquake intensity at the epicenter. Instrumental data on the earthquake hypocenter and macroseismic manifestations are presented. The wave pattern of the seismic signal and the historical seismicity are described, the mechanism of the hypocenter is calculated, and the tectonic position of the epicentral zone is considered.

The strong earthquake of 26 November 2019 (MW6.4) and its associate active tectonic of Durresi Region in Albania.

<p>On November 26, 2019, a strong earthquake (Mw6.4) occurred about 16 km, north of the Durresi city in the Adriatic Sea, and 35 km NW from the capital city of Tirana, in the western part of Albania. The main shock of November 26 at 15:20 (UTC) was followed by a great number of aftershocks.<br>The main event is not a shallow one, with the hypocentral depth at 39 km. This fact explains the localized destruction, not only in the epicentral zone but in a larger zone. This earthquake expresses the increase of recently seismic activity of the Adriatic seismogenic zone. The main shock has caused cracking of the earth, especially in the region where the epicenter of the earthquake is located. The largest cracks are in the vicinity of the Erzen river estuary.<br>These cracks have widths ranging from few cms to 1m and extending from several hundred meters to 1 km. The depth of cracking in some cases reaches into 2 meters. Those cracks are numerous and often create parallel systems between them that follow the current river bed or traces of the old river beds (paleoalvei).<br>Liquefaction phenomena have been observed extensively in the area between the villages of Juba and Hamallaj. In this area, there have been observed outflows of pressure water associated with sand and clays. The height of the water has often reached up to 1 meter around the water wells. The phenomenon of liquefaction in these areas has been associated with soil cracks of several cms wide and several tens of meters long.<br>Based on the neotectonic mapping and the focal mechanism of the mainshock, strike 219°, dip 40°, rake -90°, it is considered that the seismotectonic source that generated thisearthquake is related to NW-SE longitudinal tectonic of the Adriatic Sea. Based on the focal plane solutions provided by the IGEWE website, the mainshock was generated by the activation of an NW-SE striking thrust fault with the compression axes in the NE-SW direction.</p><p>Sea Adriatic neotectonic extend from Dalmatic coast to Ionian coast is an ancient tectonic, a reverse fault thrust, thus activated during the Quaternary geologic period to the present day, occasionally with strong earthquakes. The seismic movement has also caused a 10 cm elevation of the terrain in the epicenter of the earthquake, which has been accompanied by a coastline retreat in this area (Hamallaj beach).<br>The 21 September and 26 November 2019 earthquake sequences, as well as the 1926 seismic event that took place in the Durresi region, exhibit a rough NW−SE-trending structure, which is an active seismotectonic zone in western Albania, therefore constituting a threat for nearby urban areas.</p>

Advances in earthquake-swarms monitoring networks WEBNET and REYKJANET

<p>The IG CAS in cooperation with IRSM CAS operates two local seismic networks deployed to monitor the seismic swarms in West Bohemia/Vogtland, Czechia and Reykjanes Peninsula, Iceland. </p><p>WEBNET monitors the region of West Bohemia since 1991 developing from 4 short period stations to 24 broadband stations today. The seismoactive region West Bohemia/Vogtland lies in the border area between Czechia and Germany in the western part of Bohemian Massif. It is an intra-continental area with persistent swarm-like seismicity but rarely also main-shock after-shock sequences may occur. </p><p>REYKJANET local seismic network is situated in Reykjanes Peninsula on Southwest Iceland. The area is an onshore part of the mid-Atlantic plate boundary between the North America and Eurasia Plates. The seismic activity of Reykjanes peninsula is represented by typical main-shock after-shock sequences as well as earthquake swarms. The REYKJANET network was built in 2013 and it consists of 15 stations placed around the epicentral area.</p><p>Both networks have been substantially upgraded during the last years. In case of REYKJANET the replacement of old sensors and digitizers with new ones made the operation easier and ready for near future plan to stream the waveform files in real time. WEBNET network which was long years divided into two subnets – on-line permanent stations and off-line autonomous stations, was recently homogenized by eco-powering and 4G LTE data connecting of the off-line stations. Additonally, the micro network HORNET was deployed within the WEBNET epicentral zone to monitor Horka water dam.</p><p>Data from both above mentioned networks are automatically searched for seismic events by the neural-network-based detector designed by Doubravová et al. (2016, 2019) providing event list with completeness magnitude Mc=0 for REYKJANET and Mc=-0.5 for WEBNET. The main difference of sensitivity is given by different noise levels of the two networks.</p>

Using seismic attributes in seismotectonic research: an application to the Norcia <i>M</i>_w = 6.5 earthquake (30 October 2016) in central Italy

In seismotectonic studies, seismic reflection data are a powerful tool to unravel the complex deep architecture of active faults. Such tectonic structures are usually mapped at the surface through traditional geological surveying, whilst seismic reflection data may help to trace their continuation from the near surface down to hypocentral depths. On seismic reflection data, seismic attributes are commonly used by the oil and gas industry to aid exploration. In this study, we propose using seismic attributes in seismotectonic research for the first time. The study area is a geologically complex region of central Italy, struck during 2016–2017 by a long-lasting seismic sequence, including a Mw 6.5 main shock. Three vintage seismic reflection profiles are currently the only ones available at the regional scale across the epicentral zone. These represent a singular opportunity to attempt a seismic attribute analysis by running attributes like the “energy” and the “pseudo-relief”. Our results are critical, as they provide information on the relatively deep structural setting, mapping a prominent, high-amplitude regional reflector interpreted as the top of basement, which is an important rheological boundary. Complex patterns of high-angle discontinuities crossing the reflectors have also been identified by seismic attributes. These steeply dipping fabrics are interpreted as the expression of fault zones belonging to the active normal fault systems responsible for the seismicity of the region. Such peculiar seismic signatures of faulting are consistent with the principal geological and tectonic structures exposed at surface. In addition, we also provide convincing evidence of an important primary tectonic structure currently debated in the literature (the Norcia antithetic fault) as well as several buried secondary fault splays. This work demonstrates that seismic attribute analysis, even if used on low-quality vintage 2D data, may contribute to improving the subsurface geological interpretation in areas characterized by limited and/or low-quality subsurface data but with potentially high seismic hazard.