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A 3D model of the crustal structure of the region including the Chukchi Borderland with the adjacent ocean and Chukchi‒Alaska Shelf has been compiled and calculated. A specific feature of the crustal structure consists of three-sided isolation of the Chukchi Borderland and a transitional zone from the south connecting the Chukchi Borderland with the Chukchi‒Alaska Shelf. The connection between the Chukchi Borderland and Wrangel Rise of the Chukchi Shelf is traced through the North Chukchi Rise located between the North Chukchi Trough and the Hanna Trough. Clockwise rotation of the Chukchi Borderland began in the Early Cretaceous, because basalts at the bottom of sedimentary strata sections along the eastern and southern boundaries of the Chukchi Basin have reversed magnetization: their outpouring occurred before the beginning of the Cretaceous superchron, earlier than 121 Ma. Near the upper boundary of the Neocomian, there was a large-scale shear displacement of crustal blocks along the eastern boundary of the Chukchi Rise, which had a thrust pattern before that. The 3D model demonstrates that the Chukchi Borderland and Chukchi Basin are natural components of the continental margin, since they have a strong geological connection with the continental masses of the Chukchi Shelf. [ABSTRACT FROM AUTHOR]

Gujarat region (India) was struck by an earthquake of magnitude 5.3 on June 14, 2020 at 14:43 UTC near Bhachau city in Kachchh district in the state of Gujarat, with a depth of 20 km at the epicentre of 23.38° N, 70.36° E. In order to study the earthquake precursors for this event, data from the Induction Coil Magnetometer (LEMI-30) installed at the Badargadh Multi-Parameter Geophysical Observatory (MPGO) was analyzed for the period from January 1 to June 16, 2020. This station is located ~20 km from the epicentre of this earthquake. We observed that a clear geomagnetic burst was identified in the raw data of the Bx and By components in the LEMI-30 data before this earthquake. Geomagnetic amplitude bursts were identified 6 to 18 days and 2 days before this earthquake with a frequency of 0.01 to 0.02 Hz. Polarization ratio (PR) analysis revealed an anomalous signal on June 11, 2020 with PR values increasing to 1.4. The planetary index (Kp) and disturbance storm time index (Dst) due to the Sun‒Earth interaction are also very low (Kp = 0.3 and Dst = –6 nT) from June 10 to 16, 2020. In order to understand the dynamics of seismic processes, fractal dimensional analysis is also applied to magnetic data. Fractal dimension values also corroborate with the results of PR analysis, which showed a similar anomaly on June 11, 2020. The ULF geomagnetic data was further analyzed by applying the band-pass filtered data instead of the raw data in the period range from 10 to 45 seconds and derived the Z/X amplitude ratio in the Pc3 band. We found an upward trend and a downward trend from June 10, 2020. Enhanced polarization ratios were detected in the reconstructed components using the EMD technique which are linked to the current earthquake. It has been clearly demonstrated that the EMD method can be used to isolate noise and thus improve the identification of simultaneous short-term geomagnetic variations/anomalies. Therefore, in our study, we have clearly differentiated their origin, whether external (the Sun‒Earth interactions) or internal (local changes in conductivity in the area of the preparation). [ABSTRACT FROM AUTHOR]

The article presents the results of a study of modern geodynamic movements in bottom structures of the White Sea (Baltic Shield). Based on expeditionary work in the White Sea, data were obtained on the formation of the seabed relief and thickness of unconsolidated sediments under the influence of modern seismotectonic events and geodynamic movements, as well as long-term neotectonic processes. It is shown that the Kandalaksha Bay depression is a modern graben developing along faults activated in the Quaternary. Graben development continues to the northwest, where a new Quaternary structure is being formed. Signs of modern geodynamic movements have been identified. The authors demonstrate the role of disjunctive tectonics in the formation of slopes and tectonic structures transverse to the strike of the bay, morphologically represented by relief ridges cutting the Sredny Ludy rise in Kandalaksha Bay. The influence of modern geodynamic processes on the distribution of thicknesses of Quaternary sediments of various genesis and the mosaic distribution of modern bottom sediments has been established. The influence of gravitational processes involved in the formation of underwater landslides, leading to the appearance of abnormally thick layers of the unconsolidated sedimentary cover, has been studied. [ABSTRACT FROM AUTHOR]

The Western Desert of Egypt is an area of the Sahara which lies west of the River Nile, up to the Libyan border, and south from the Mediterranean Sea to the border with Sudan. It is mostly rocky desert; the desert covers 2/3 of the land of Egypt. Its highest elevation is 1000 m in the Gilf Kebir plateau to the far south‒west of Egypt, on the borders of Egypt, Sudan and Libya. We used to collect available data of the earthquakes, which occurred in or near the western part of Egypt during the period from 1900 to 2018, to investigate the seismic activity and its relationship to the geology and tectonics of Egypt. The frequency statistical analysis is used to calculate the frequency-magnitude relation for the data in this period. The results indicate that about 28 earthquakes are equal or exceed Richter magnitude M ≥ 4 every 100 years. The whole Western Desert is characterized by low to moderate levels of seismic activity. The southern part of Western Desert is considered to be seismically active. The source mechanism for some earthquakes was estimated using the waveform data recorded from the records of the Egyptian national seismograph stations and our results show the normal faulting mechanism with minor strike-slip component. The NNW trend has been chosen as a preferred rupture plane in consistence with surface and subsurface faults and microearthquake seismicity in the epicentral area as well. [ABSTRACT FROM AUTHOR]

The transitional zone of the marginal seas of the Asia‒Pacific region is a significant object for geological research, the large deposits of hydrocarbons (oil, gas, gas condensate, gas hydrates) have been discovered in the regions of the transition zone. The article gives an interpretation of the main gas-geochemical and geological tectonic regularities of the occurrence and distribution of methane and carbon dioxide fields of different types on the shelf of Sakhalin Island. A study of the gas-geochemical parameters of the emitted gases in the "continent‒shelf" transit zone was carried out based on comparison of field studies and satellite observation data. The data of satellite observation of Sakhalin Island and its shelf are presented to identify the relationship between seismic events and changes in the level of methane concentration in the atmospheric air (in particular, on the example of the methane discharge regime of the Yuzhno-Sakhalinsky mud volcano). Remote sensing data are compared with the results of the field studies, and an assessment is made of the potential using satellite observation methods for studying the gas geochemical composition of the methane and carbon dioxide field. The results obtained can make it possible to refine the assessment of the emission of climatically active gases, and also bring the significant incentive to the development of the Russian Federation project "Far Eastern Marine Carbon Monitoring Plots Consortium." [ABSTRACT FROM AUTHOR]

This article presents the results of studies of the source of a strong earthquake in Central Tuva. The studies were carried out using the structural-geomorphological, paleoseismological, and historical-paleoseismological methods. Primary information about the source and its location was found in folklore sources with a toponymic reference, based on which traces of the earthquake were found and mapped afield. Traces of earthquakes are confirmed by seismic ruptures in the Ulugkhem active fault zone and seismogravity evidence. This event is preliminary dated to 1715‒1758; magnitude Mw = 6.5‒7.0. The intensity of the earthquake at the epicenter reached VIII–IX (ESI-2007 scale). The consequences of the catastrophic explosion of 1950 in the Ulugkhem active fault zone, which led to human casualties and destruction, were mapped. The results of the research make it possible to clearly define the northern boundary of the Kyzyl intermountain basin as a fault with sinistral overthrust reverse fault kinematics of displacements in the Holocene. The identification of the epicentral zone of a historical earthquake is necessary to assess the seismic hazard of the most densely populated region of the Republic of Tuva. [ABSTRACT FROM AUTHOR]

The article presents the results of the first comprehensive geological and geophysical studies of active tectonics in the western part of Wrangel Island, carried out during the expedition of the Northern Fleet and the Russian Geographical Society in 2020. Our research was conducted at Cape Thomas. An active fault at Cape Thomas was identified as an active sublatitudinal fault, along which there had been the repeated movements, thrusting the mountain ridge onto the coastal lowland in the southern direction. In contrast to the Paleozoic‒Mesozoic southward-dipping structures, the active reverse–thrust has the north-dip and reflects displacement of the mountain range from north to south. The studies carried out allow us to reasonably believe that the potential source of strong earthquakes extends along the boundary of the growing tectonic block of the Western Plateau and southern coastal lowland of Wrangel Island. The data significantly refine the dynamics and kinematics of young tectonic movements on Wrangel Island, but are in conflict with low seismic activity. It has been suggested that the potential source is currently in the seismic quiescence stage. [ABSTRACT FROM AUTHOR]

Seismic zoning maps of Azerbaijan, compiled using the genetic (seismotectonic) method, are analyzed. The peculiarities of this method are considered as applied to a fault along its length. The genetic method is based on the assumption that at each point of an active (seismogenic) tectonic fault, an earthquake can occur with a magnitude (M) equal to the maximum magnitude (Mmax) of a recorded earthquake. To identify the source zones of strong earthquakes, the author developed a method for determining seismogenic (active) zones of deep tectonic faults from weak seismicity. This method and the available data on the activity of deep-seated tectonic faults were used to assess the seismic hazard of Azerbaijan and adjacent territory of southern Russia. It has been established that seismic shaking on the surface of the territory regional study is of wide differentiation in space according to the degree of its manifestation. [ABSTRACT FROM AUTHOR]

The paper considers the results of a study of modern strong earthquakes (1991 Racha, 2006 Olyutor, 2003 Altai, and 2011–2012 Tuva) according to a single methodological plan. The need for such studies is dictated by constantly increasing requirements on the accuracy of predicting hazardous natural impacts. Analysis of the seismotectonic conditions of the locations of sources of strong earthquakes made it possible to identify geological structures and thus form an idea of the morphotectonic criteria for identifying potential sources in other regions. Modern earthquakes have continued the development of different-scale tectonic structures directly expressed in the modern relief. These activated structures form regular combinations inscribed in morphostructures of different scales. The displacements during modern earthquakes continue the development of morphostructures traced throughout the Middle Pleistocene–Holocene. The size and number of morphostructures involved in seismic activation are directly related to the magnitude of an event and reflect the specific hierarchical level of seismogenesis. In order to assess the seismic hazard, it is important that the presence or absence of pronounced active faults on the surface does not directly reflect the level of seismic hazard. [ABSTRACT FROM AUTHOR]

Being a part of the eastern Mediterranean, northern Lebanon and northwestern Syria is a seismotectonically active region due to the juxtaposition of several plate boundaries, the existence of many active faults, and the intense seismicity generated along rifting, transform, and convergent plate boundaries. We applied a tomographic inversion on seismic body wave arrivals recorded at 12 seismic stations distributed in the northern part of Lebanon and northwestern Syria to study the P- and S-wave velocity (Vp, and Vs) structures and the seismogenic behavior of the upper portion of the lithosphere. The seismic data comprise 4855 and 2950 P- and S-wave arrivals, respectively, generated by 605 local crustal earthquakes which occurred mainly along the Yammouneh Fault and splays in the Eastern Mediterranean. The crustal structure is highly heterogeneous down to the upper mantle depths. Low-velocity (low-V) anomalies are widely distributed especially along the active faults delimiting the boundary between the Arabian and African plates and areas of thick sedimentary deposits and Cenozoic volcanics. Results of the checkerboard resolution test and hit count coverage indicate that the mapped velocity anomalies are reliable features. Furthermore, they are generally consistent with many geological and geophysical investigations which have been detected beneath the study area by other researchers including the emplacement of ophiolite rocks, Cenozoic volcanics, inefficient Sn propagation, low Lg Q values, and low seismic wave velocities. [ABSTRACT FROM AUTHOR]

Geometric and seismic parameters of the Qoshadagh Fault (QDF) were investigated to evaluate seismic hazard along this fault, which consists of three segments. The central E–W striking, dextral-reverse segment is the longest and terminates at both ends into NW–SE striking splay arrays. Both eastern and western splay arrays form locally transtensional bends. Paleoseismic data obtained from three excavated trenches across the fault combined with dated offset geomorphic features revealed that the central segment experienced at least 5 surface rupturing earthquakes during the past 2.5 ka, with maximum moment magnitude of Mw = 6.8 ± 0.2. The mean recurrence interval for the identified paleoearthquakes is 452 ± 143 years (±2σ) and the calculated amount of slip per event is ca. ≈0.85 m. These results imply that the QDF slips at an average rate of 1.9 ± 0.1 mm yr–1 for over the past 2.5 ka. The obtained values define the seismic behavior of the fault and are essential to remediate ensuing seismic risks. [ABSTRACT FROM AUTHOR]

The objective of this study is to evaluate the seismic hazard at the Esfarayen-Bojnurd railway using the probabilistic seismic hazard assessment (PSHA) method. This method was carried out based on a recent data set to take into account the historic seismicity and updated instrumental seismicity. A homogenous earthquake catalogue was compiled and a proposed seismic sources model was presented. Attenuation equations that recently recommended by experts and developed based upon earthquake data obtained from tectonic environments similar to those in and around the studied area were weighted and used for assessment of seismic hazard in the frame of logic tree approach. Considering a grid of 1.2 × 1.2 km covering the study area, ground acceleration for every node was calculated. Hazard maps at bedrock conditions were produced for peak ground acceleration, in addition to return periods of 74, 475 and 2475 years. [ABSTRACT FROM AUTHOR]

Based on seismological, geodynamic, and seismotectonic data on a series of strong earthquakes which occurred in 2016-2017 in central Italy, the tectonic positions and geological manifestations of these events are determined. The aftershock processes of these earthquakes are studied. It is found that epicentral clouds of mainshocks and aftershocks almost overlapped each other, so these earthquake sources in aggregate can be classified as a high-magnitude earthquake swarm. [ABSTRACT FROM AUTHOR]

The results of studying traces of ancient seismic catastrophes in epicentral zone of the 1991 Racha earthquake are set forth. The source of this earthquake is noteworthy, because it reflects the main tendency in the geological evolution of the region, i.e., thrusting of the southern slope of the Greater Caucasus over the basement of the Transcaucasus Median Mass. It has been ascertained that two large-scale seismic events were related to this source in the Holocene. The approximate duration of the middle Holocene event was 2300 yr (7300-5000 yr ago). The late Holocene event, including the Racha earthquake in 1991, lasted ∼1600 yr. The role of the Racha earthquake in the large-scale seismic cycle is discussed. A surprising circumstance was the absence of datings in the time interval of 2400-9500 yr ago. The lack of these datings could have been caused by the change in climate and absence of paleosoils or by deceleration of seismic activity. The results also allowed us to substantiate seismotectonic segmentation of the southern slope of the Greater Caucasus in the area under consideration. [ABSTRACT FROM AUTHOR]

An alternative explanation to the seismoactivity of Cuban faults is presented. The model is a consequence of the interaction between Caribbean and North American plates. It is made with 12 geodynamic cells form by a set of 13 active faults and their 14 areas of intersection. These cells are recognized morpho-structural blocks. The area between Eastern Matanzas and Western Cauto-Nipe is excluded because of the low level of seismic information. Cuba has two types of seismogenetic structures: faults and intersection of faults. [ABSTRACT FROM AUTHOR]