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Soil plug formation in open-ended piles due to pile driving is a widely studied phenomenon in onshore applications. The narrow diameters of traditional onshore piles ranging from 0.5 to 1.5 m facilitate plug generation during installation and transfer of enhanced confining stresses across the whole body of the soil plug. Offshore wind monopiles with larger diameters and smaller aspect ratios may not enhance confining stress within the soil plug as effectively as their onshore counterparts. Monopiles are currently the most widespread foundation in the offshore wind sector including in seismic areas. Earthquake shaking can lead to accumulation of excess pore pressure and subsequent liquefaction of the soil retained inside the plug. This research investigates the influence of monopile diameter and confining stress on the development of earthquake-induced excess pore pressure within the soil plug using fully coupled time domain Finite Element Analysis. The results presented in this paper reveal lower accumulation of earthquake-induced excess pore pressure in soil plugs subjected to confining stress. However, the influence of additional horizontal stress caused by monopile driving on the generation of excess pore pressure within the soil plug diminishes as the monopile diameter is progressively increased. [ABSTRACT FROM AUTHOR]

Different catalogues of earthquakes are available for the Indian region besides regional catalogues for the Gujarat region. The limitations of these and other historical catalogues have been discussed in this paper for earthquake hazards and other studies. Keeping in view that these historical catalogues have been successful in explaining the recent occurrence of a few earthquakes like Coimbatore (1900), Hyderabad (1983), Bangaluru (1985) and Jabalpur (1997), the study has been extended to the Gujarat region. In this paper, therefore, an attempt has been made to correlate the historical data of the felt earthquakes in the Gujarat region from all the available sources with instrumental data to examine the recurrence of the earthquakes. It has been found that in addition to the seismically active Kutch region and Narmada and Cambay rifts, there is a tendency for earthquakes to recur in many districts of Gujarat for which felt data from historical times is available. The seismicity map prepared by the Institute of Seismological Research (ISR), Gandhinagar based on the Seismic Telemetry (2006–2020) shows scattered seismicity over the whole of Gujarat region besides active seismicity in the Kutch region. This data when combined with that from the catalogue prepared by the National Centre of Seismology provides greater confidence for earthquake hazard studies It has also been found that the coastal regions of Saurashtra and south Gujarat are more prone to swarm types of earthquakes. [ABSTRACT FROM AUTHOR]

Today's earthquakes are the most direct manifestation of the latest tectonic activity and are the most powerful tool to understand the characteristics of nonrigid deformation within a continent. Particularly, the newly formed faults that have been active since the Late Pleistocene are characterized to have low development maturity, poor connectivity in geometric structure, and obvious difference in strike/depth dip in different sections. Therefore, earthquakes can reveal their three-dimensional space changes, especially the characteristics of brittle-ductile transition depth. Earthquakes can also promote the understanding of the preparation and earthquake generation process of newly formed active faults. The newly formed strike-slip active faults in the Bohai Bay Basin have experienced many strong earthquakes, including the Tangshan MS7.8 and the three Ninghe MS≥ 6.2 earthquakes. The crustal brittle-ductile transition depth revealed by these earthquakes has an important practical significance to understanding the seismogenic mechanism and activity of the region. In this paper, the new fault in the Baodi Miaozhuang uplift in the Bohai Bay Basin is taken as the target fault. In addition, the 2012 Baodi MS4.0 and MS3.5 earthquakes in the Baodi uplift and the 1976 Ninghe MS6.2 and MS6.9 and the 1977 Ninghe MS6.2 earthquakes in the Miaozhuang uplift are taken as the research objects. Finally, the CAP method is used to study the source mechanism solution and the source depth of the Baodi MS4.0 and MS3.5 earthquakes based on the waveform data from the Capital Circle Digital Seismic Network. The double difference method is used to locate the source positions of two earthquake sequences by employing the Sp converted wave of near earthquakes to accurately determine the source depth. Moreover, combined with other data, the seismogenic mechanism of earthquakes in this area and the brittle-ductile transition depth of new fractures are discussed. The following results were found. (1) The source properties of the Baodi MS4.0 and MS3.5 earthquakes are not completely consistent with the known faults on the exposed surface of the Baodi Miaozhuang uplift. Combining the research results of the source parameters of the three Ninghe earthquakes having an MS ≥ 6.2, it is inferred that they all occurred in the Baodi-Ninghe deep fault. (2) Based on the models of electrical structure and rheological structure in the focal area, the five significant earthquakes in Baodi Miaozhuang uplift reveal that the brittle-ductile transition depth of the Baodi-Ninghe deep fault is about 15 km. (3) Based on the dynamic evolution process of the Bohai Bay Basin and relevant deep geophysical exploration data, it is hypothesized that the seismic activity in this area is mainly the result of the Baodi-Ninghe deep fault and deep fluid actions. [ABSTRACT FROM AUTHOR]

The paper presents the results of retrospective and tectonophysical analysis of the Tokachi-Oki earthquake source area on the September 25, 2003 (Mw = 8.3). Particular attention is paid to the Hidaka tectonic belt, the structures of which were affected by the Tokachi-Oki earthquake. The load–unload response ratio (LURR) method was applied at sufficient spatial (a square with a side of about 400 km) and temporal (continuous 20-year period) intervals to consider the results reliable. The forerunners of the Tokachi-Oki earthquake on the September 25, 2003, were revealed (on average, two years before the seismic event), which strictly determined the earthquake location. The data obtained with The method of cataclastic analysis (MCA), together with LURR data, made it possible to establish the stages of instability development in the Hidaka collision zone. The Hidaka tectonic belt became outlined by destruction zones (mainly horizontal compression) from 1997 to 2003 (up to the Tokachi-Oki earthquake). LURR anomalies were detected along the belt a couple of years before the earthquake. The prediction of the Tokachi-Oki earthquake by the LURR method is one of the most reliable in our practice. [ABSTRACT FROM AUTHOR]

The geological activity in Sichuan and Yunnan of China is intense, and large earthquakes such as the Tonghai earthquake in 1970 have caused huge casualties and economic losses. Therefore, it is significant to reduce the long-period earthquake damage of dams and high-rise buildings to reproduce the near-fault long-period ground motion characteristics of the Tonghai earthquake. In this paper, the finite difference method is used to predict the long-period characteristics of the Tonghai Ms 7.8 earthquake. Considering the uncertainty of the initial fracture point, number of asperities, and slip angle, 18 seismic scenarios are established. The predicted results are verified by comparing intensity, attenuation relation and pulse probability distribution. At the same time, based on the velocity pulse recognition method, the pulse probability distribution of the near-field is obtained. We selected six seismic scenarios with high probability from 18 seismic scenarios. Our results show that the spatial distribution and pulse probability distribution of near-field simulated ground motion is significantly affected by the initial rupture positions. After the characteristics of the largest asperity on the fault are determined, the remaining asperities have limited influence on the spatial distribution of simulated ground motion. This study expands the application scope of the finite difference method, which can simulate the seismic intensity characteristics of destructive earthquakes in areas with few seismic records. [ABSTRACT FROM AUTHOR]

The temporal distribution of earthquakes provides important basis for earthquake prediction and seismic hazard analysis. The relatively limited records of strong earthquakes have often made it difficult to study the temporal distribution models of regional strong earthquakes. However, there are hundreds of years of complete strong earthquake records in the North China Seismic Zone, providing abundant basic data for studying temporal distribution models. Using the data of M ≥ 6.5 earthquakes in North China as inputs, this paper estimates the model parameters using the maximum likelihood method with Poisson, Gamma, Weibull, Lognormal and Brownian passage time (BPT) distributions as target models. The optimal model for describing the temporal distribution of earthquakes is determined according to Akaike information criterion (AIC),and Kolmogorov–Smirnov test (K–S test). The results show that Lognormal and BPT models perform better in describing the temporal distribution of strong earthquakes in North China. The mean recurrence periods of strong earthquakes (M ≥ 6.5) calculated based on these two models are 8.1 years and 13.2 years, respectively. In addition, we used the likelihood profile method to estimate the uncertainty of model parameters. For the BPT model, the mean and 95% confidence interval of recurrence interval μ is 13.2 (8.9–19.1) years, and the mean and 95% confidence interval of α is 1.29 (1.0–1.78). For the Lognormal model, the mean value and 95% confidence interval of v is 2.09 (1.68–2.49), the mean value exp (v) corresponding to earthquake recurrence interval is 8.1 (5.4–12.1) years. In this study, we also calculated the occurrence probability of M ≥ 6.5 earthquakes in the North China Seismic Zone in the future, and found that the probability and 95% confidence interval in the next 10 years based on the BPT model is 35.3% (26.8%-44.9%); the mean value and 95% confidence interval of earthquake occurrence probability based on the Lognormal distribution is 35.4% (22.9%-49.7%); the mean probability and 95% confidence interval based on the Poisson model is 53.1% (41.1%-64%). The results of this study may provide important reference for temporal distribution model selection and earthquake recurrence period calculation in future seismic hazard analysis in North China. [ABSTRACT FROM AUTHOR]

The paper is devoted to the assessment and forecast of the occurrence of submarine landslides on the shelf of southeastern Vietnam. The prediction is based on the analysis of the existence of slip tendency on known faults, studying the magnitude of possible relative vertical and horizontal displacements in the Earth's crust, considering the slope steepness of bottom relief and surface of landslide deposits, as well as assessing the probability of reactivation of faults and likely earthquake zones. The results of the study allow making decisions on combating submarine landslides, reducing damage to people and property in coastal areas. Based on the information obtained, not only submarine landslides but also other geological hazards in areas of the Vietnamese continental shelf can be predicted. [ABSTRACT FROM AUTHOR]

This paper presents an analysis of the identification of potential seismic damage in an area called Tanah Patah, Bengkulu City, Indonesia. This study is initiated by conducting site investigation and geophysical measurements. Ground motion prediction is conducted to estimate peak ground acceleration which is then used to estimate the damage intensity level during a large earthquake. A spectral matching method to generate ground motion at investigated sites is conducted. Seismic ground response analysis to observe ground response and soil behaviour is performed. The results show that peak ground acceleration in the study area is about 0.255–0.342 g during a large earthquake. IX is this area's Modified Mercalli Intensity (MMI) level scale. Since sandy soils dominate the study area, several sites could be more vulnerable to undergoing liquefaction. The thickness of potentially liquefiable soils is about 8.6–12.8 m. The results could help local governments develop spatial plans in the study area. [ABSTRACT FROM AUTHOR]

This paper reports results of mathematical modeling applied to the stress and strain in epicentral zones before and after the large earthquakes that occurred on June 22, 2002 in the Qazvin Province, northwestern Iran (Mw = 6.4) and the Gujarat, India earthquake of January 26, 2001 (M = 6.9). The modeling relied on a method for calculating stress and strain in a blocky elastic isotropic heterogeneous medium disturbed by a set of faults that are due to an external tectonic stress field. The boundary conditions were specified based on geological and seismological data. It has been shown that the epicenters of large crustal earthquakes occur in zones of high stress concentration at the ends of tectonic faults. Rupture occurs when the relationship between acting tectonic stresses satisfies the requirement σyy/σxx >3, thus connecting zones of high stress. The evolution of the aftershock process is controlled by the stress drop caused by a new rupture, while the resulting aftershock clusters are in spatial correlation with the stress drop zone. The new rupture propagates in the direction of dominant tectonic fault orientation in the region. We show a relationship to exist between rupture length and the possible retrospectively predicted location and magnitude of the earthquake depending on the elastic energy buildup and its possible release under specified structural tectonic conditions. [ABSTRACT FROM AUTHOR]

Abstract—The paper presents the results of many years of research on the compilation of a consolidated, refined, unified earthquake catalog for the western sector of the Russian Arctic for the entire instrumental observation period, in particular for the period from 1908 to 2020. The catalog includes data on recent seismicity in areas previously unavailable for detailed seismic monitoring. Based on the results of the study, we were able to more accurately determine the spatial distribution of seismicity in the region and compare the instrumental data with parameters of lineament-domain-focal (LDF) models of the General Seismic Zoning maps (GSZ, from Russian term abbreviated as OSR)—OSR-97 and OSR-2016. In the western sector of the Russian Arctic, the highest seismicity is observed in the continent-ocean transition zone, in the Belyi (Kvitøya) Island, Novaya Zemlya and Severnaya Zemlya archipelagos. The very shelf of the Barents and Kara Seas is characterized by rare and scattered seismicity. The configuration, the maximum possible magnitudes, and the depths of the seismogenic layers in the LDF models of OSR-97 and OSR-2016 maps are not always consistent with the instrumental data and need a correction. The consolidated refined earthquake catalog can be used as a basis for the further research aimed at seismic hazard assessment of the territory, construction of geodynamic models, and study of the stress-strain state of the Earth's crust. [ABSTRACT FROM AUTHOR]

Identifying pre-seismic atmospheric and ionospheric anomalies is of research importance but also meets difficulties, especially for earthquakes with varying magnitudes, focal depths and focal mechanisms. In this paper, atmospheric‒ionospheric disturbances associated with earthquakes in Nepal (April 25, 2015, M = 7.8 and May 12, 2015, M = 7.3) are investigated using atmospheric and ionospheric parameters. Ionospheric (vertical total electron content (VTEC)) and atmospheric (outgoing long wave radiation (OLR), cloud mask, vertical temperature gradient (VTG)) parameters are archived from IGS GPS stations and INSAT 3D data from Indian Meteorological Department (IMD) of Ministry of Earth Sciences, Government of India. The abnormal VTEC signal was noticed 3 days and 10 days prior to April 25, 2015 event and 2 days and 6 days prior to the May 12, 2015 event. Inter-quartile range (IQR) and associated running median over one day were determined as the upper limit reference to a signature of VTEC for the 51-days period of the Nepal earthquake, it can be clearly observed that the total electron content (TEC) has increased from the limits of UB (upper bound) at the stations closest to the earthquake epicentre such as LCK-4, LHAZ than the far stations such as IISC, HYDE, SGOC and URUM. Prior to these earthquakes, UB observed a 54‒60% increase in relative amplitude of VTEC. The overall geomagnetic storm condition was thoroughly examined using the global planetary index (Kp) and storm time disturbance index (Dst) over the 51-days period. The IQR range method was used to analyse its abnormal positive and negative signals. We found no geomagnetic signatures caused by geomagnetic storms during the seismic regime The OLR varied from 240 to 340 watts/m2 observed 4 days before the event. The vertical temperature gradient varied from 4.3 to 23.2 K. Daily variations of 51 days for the OLR showed good anomalous atmospheric responses a few days before the event. The shallow depth of the earthquake gives the best coupling, releasing a large amount of energy from the seismic zones, and could be a causal factor in the enhancement of anomalous VTEC patterns. [ABSTRACT FROM AUTHOR]

This paper is the first in a series of studies generalizing the Map of Expected Earthquakes (MEE) medium-term earthquake forecast method and analyzing the prospects for its further improvement. Over the past 35 years, the MEE method has been used in seismically active regions around the world with different tectonic conditions and seismic regimes. The average prognostic efficiency of the algorithm was shown to be 2.5 times higher than for random guessing. The MEE can be further improved and upgraded. The new methods of data processing to be implemented into the upgraded MEE will significantly increase the amount of analyzed data, take into account the specific signs of the seismic process at different depths, use lineament–domain–focal (LDF) models of the structure of seismically active zones as stationary prognostic criteria, and build three-dimensional distributions of the probability of strong earthquakes. The improvement will involve an expansion of the list of used seismological precursors that have a physically justified link with the earthquake preparation process and the development of formalized techniques for identifying these precursors in the prognostic practice. [ABSTRACT FROM AUTHOR]

We consider some characteristics of seismicity in the region of Southwest Alaska. The aftershock zones of the Simeonof (July 22, 2020, Mw = 7.8) and Chignik (July 29, 2021, Mw = 8.2) earthquakes are identified. The characteristics of ring-shaped seismicity structures, which formed in a few decades prior to the Chignik earthquake, are described. The location and magnitude of a large event, which could be prepared to the east of the Simeonof earthquake rupture zone, was predicted in (Kopnichev and Sokolova, 2021a) based on the parameters of these structures. An estimate of the expected magnitude (Mw = 8.2 ± 0.2) was obtained using correlation dependences between the parameters of ring-shaped structures and the magnitudes of large and great earthquakes that occurred in the East Pacific region. This forecast, which was made on the basis of the data obtained prior to October 21, 2020, was presented in the mentioned paper, which was accepted for publication before July 29, 2021. We consider possible changes of the parameters of ring-shaped structures immediately prior to the Chignik earthquake and discuss geodynamic processes that can lead to the formation of ring-shaped structures. [ABSTRACT FROM AUTHOR]

It is a key to know mechanical environment (ME) of pre- and post-rupture fault of giant earthquakes at subduction zones for predicting earthquake and tsunami disaster. However, we know little about its details till now. In this paper, using the inverted stress change three hours before and three hours after the mainshock in the rupture zone of the 2011 Tohoku-Oki Mw 9.0 earthquake, we show a quantitative integrated ME in the rupture zone, including principal stress, pore-fluid pressure and friction strength. We discover from this environment a large asperity composed of two asperities induced by relatively high friction coefficients and relatively lower pore-fluid pressures. The integrate ME quantitatively explained the reasons of the overshoot and relatively lower shear strength of the trench, which caused huge displacement and tsunami at the trench. We suggest that the asperities favor the horst and graben structure system which provides a geology environment for interseismic stress accumulation and thus for breeding the megathrust tsunami earthquake. [ABSTRACT FROM AUTHOR]

A destructive earthquake, especially if it occurs in areas of high seismic risk, in the form of certain factors, has a significant impact on the environment, including biodiversity. These factors (earthquake effects) are determined by the strength of the earthquake (manifestations of intensity on the earth's surface), local conditions (geomorphological, geological structure, level of urbanization and seismic risk, etc.), disaster-zone recovery processes (fast and effective recovery, localization and prevention of secondary consequences, environmental protection, state opportunities and political decisions, etc.). It is clear that these three important basic conditions of effects are different in different seismic regions and countries, which means that the impact of an earthquake on the environment is different. To consider the features and factors of the impact of an earthquake on the environment, the 1988 Spitak earthquake—one of the most detailed and comprehensively studied earthquakes in the world—was taken as a test object. The main purpose of this article is to highlight in more detail and more fully the possible natural and human factors of the impact of a strong earthquake on the environment and predict the extent of these impacts. Thirty-six major earthquake factors affecting the environment have been identified, which are conditionally divided into three main groups according to the time of formation and genesis: (a) purely seismic, (b) secondary seismic, and (c) post seismic. The paper also attempts to assess possible changes in these factors depending on global warming and a decrease in precipitation. [ABSTRACT FROM AUTHOR]

Central Tibet constitutes part of the central part of the Qinghai–Tibetan Plateau, which is one of the highest seismically active areas in China. This paper discusses the regularity of seismic activity in this area. Based on a stratified viscoelastic earth model, we calculated the Coulomb stress changes imparted from four strong earthquakes (M ≥ 6.3) along the Bengco–southeastern piedmont of the Nyainqentanglha mountain fault zone in this region. The result shows that the study area may be entering a new active period from 2020. There was a trigger between the strong earthquakes (M ≥ 6.3) on the Bengco fault zone. The post-seismic viscous relaxation effect of a strong earthquake had a significant impact on subsequent earthquakes (M ≥ 6.3). In the next 100 years, the Coulomb stress loading is more than 1.0 MPa in the northwest section of the Bengco fault and the central part of Nimu segment of the southeastern piedmont of the Nyainqentanglha mountain fault. Thence, strong earthquakes may occur along these fault segments. The maximum magnitude of the earthquake could be M6.7 in the next 100 years. [ABSTRACT FROM AUTHOR]

The Yuzhno-Sakhalinsk Seismological Regional Information Processing Center (RIPC) recently used the Richter magnitude Mwa to estimate the energy level of Far Eastern earthquakes. To date, this is the most common energy characteristic in the operational catalog of the RIPC. The basis is digital waveforms of regional seismic stations emulated to the characteristics of the Wood–Anderson seismograph. In the present paper, the results of determining the magnitude Mwa in Russian Far Eastern conditions are analyzed. The magnitude determination accuracy is estimated, and station corrections are obtained. The regression relation Mwa and Japanese Meteorological Agency magnitude Mj showed a high similarity between these scales. This made it possible to use Mj as the reference when studying the features of Mwa. The regional seismic network makes it possible to correctly estimate the magnitude Mwa at a regional distance (up to about 1000 km), including for deep-focus earthquakes (up to 600 km). Transfer relations between Mwa and other mass-determined regional energy characteristics of earthquakes are obtained. The Mwa scale can be used to estimate the energy level of any earthquakes in the Kuril–Okhotsk and Sakhalin regions in the magnitude range of weak and moderately strong events and is recommended for inclusion in regional earthquake catalogs for the Russian Far East. [ABSTRACT FROM AUTHOR]

This paper presents the results of a detailed study of two relatively strong seismic events, occurred on November, 22, 2016 (МW = 5.0) and April 3, 2017 (МW = 4.8) at the northeastern flank of the Baikal rift zone in the areas of the South Muya and Kalar ranges. Both the events were followed by weak aftershocks (N = 178–539, Кр ≤ 11.0), whose epicenters were densely distributed over an area. The seismic moment tensors and hypocentral depths of the mainshocks were calculated from surface wave amplitude spectra. It has been shown that their sources were formed under the influence of the subhorizontal SE–NW extension and the subhorizontal or inclined NE–SW compression. Both the earthquakes were followed by noticeable macroseismic effects at epicentral distances up to 500 km. In the area of the Baikal−Amur Railway, their shaking intensity was IV–V MSK-64. The results obtained can be used in continuous seismic monitoring at the northeastern flank of the Baikal rift zone and can contribute to an objective seismic hazard assessment of the study area. [ABSTRACT FROM AUTHOR]

For the first time, a numerical comparison of the General Seismic Zoning (GSZ) maps with the effect of earthquakes that actually occurred after the publication of the maps was carried out. The area of zones of expected intensity on the GSZ map is compared with the area of isoseists from actual earthquakes. It turned out that the isoseist area is on average by an order less than expected according to the GSZ. This paper describes possible reasons for such an overestimation and proposes ways to improve seismic hazard assessments. [ABSTRACT FROM AUTHOR]

This paper presents the effects of October 30, 2020 Samos-Aegean Sea earthquake on hydraulic structures, lifelines and industrial facilities which mainly located in the western cost of Turkey, within the borders of Izmir and Aydin Cities. These two highly populated cities are known for their importance in contributing country's economics by their industrialized areas. In addition, Izmir is the third largest city of Turkey with its high seismic hazard zone. Although some disruptions in the aftermath of the earthquake were occurred in gas and electricity services, these issues immediately identified, and all systems were managed to reoperate. Damages to the infrastructures were mainly due to the collapse of buildings and tsunami effects. No significant damages were reported on lifeline systems, large industrial facilities, and dams due to relatively low shaking intensity. [ABSTRACT FROM AUTHOR]

The goal of this paper is to describe cluster analyses of the focal mechanism solutions estimated from local and teleseismic measurements and stress inversions to support the recent and previously published studies in the investigated region, that is the Vrancea seismic zone. We have applied different established clustering methods—e.g. hierarchical density-based clustering for applications with noise (HDBSCAN) and agglomerative hierarchical analysis—to the geographical coordinates, focal depths and parameters of the focal mechanism solutions of the gathered seismic events. We have attempted to develop a fully automated algorithm for the classification of earthquakes and to support the further investigation of stress inversions. This algorithm does not call for the setting of hyper-parameters by the users, thus the contribution from any bias of the user can be reduced significantly and the time required to carry out the clustering can also be decreased. In most cases, the resulting stress tensors are in close agreement with those we found in the literature. [ABSTRACT FROM AUTHOR]

The Philippines, as part of the Circum-Pacific belt, is considered as one of the most seismically active countries in the world. Earthquake occurrence is frequent and its effects vary depending on its size. Understanding how the occurrences happen is therefore important. Stochastic models of earthquake occurrence have been used to study seismic activities in various active earthquake zones globally. In this paper, we apply Poisson hidden Markov models (PHMM) using the January 1, 1960 to January 20, 2019 earthquake data of Metro Manila, Philippines. The parameters in the models are estimated using expectation-maximization (EM) algorithm. We determine using various statistical tests that the 5-state PHMM best represents the earthquake data and implement bootstrap algorithm to validate the acceptability of its parameter estimates. Moreover, we investigate the forecasting capability of the 5-state PHMM by comparing it to the ARIMA model. Using unscaled mean bounded relative absolute error (UMBRAE), we find that the 5-state PHMM gives closer one-step ahead forecasts and is a better forecasting model for the considered data. [ABSTRACT FROM AUTHOR]

The present paper gives a scale of earthquake energy class KF that is to standardize the relevant data based on the existing scales: MS, MW, mb, KS, among many others. The conceptual novelty of the scale we propose consists in shifting the emphasis from seismometric issues that are traditional in such cases, which are concerned with the recording of seismic waves, as well as with issues arising in discussions of their generation and propagation, toward an effective use of basic energy properties of the seismic process (the Gutenberg–Richter law). In the most general case, this approach can significantly simplify the development of regression relations between different earthquake size scales, but the most promising problem consists in developing a single generalized scale. A particular solution of the problem is presented as the development of such a scale for earthquakes of Kamchatka. The KF scale rests on the energy class proposed by S.A. Fedotov (KS at the Kamchatka Branch (KB) of the National Seismological Centre, Geophysical Survey, Russian Academy of Sciences (NSC GS RAS) and on the generally accepted mb magnitude (ISC). [ABSTRACT FROM AUTHOR]

Abstract—In this paper, we explore the findings of monitoring the components of the Earth's natural electromagnetic (EM) field obtained in 2020–2021, as well as their link with rather strong seismic events within Baikal Rift Zone (in particular, the Kudarin earthquake (Dec. 9, 2020, Mw = 5.5)). During the observations of the magnetotelluric field more than one month prior to the seismic event, the increased conductivity of the tensor-sensitive parts of the sounded soil was recorded due to the displaced release of conducting fluid to the weak crust zones before the earthquake. 24 hours before the seismic event, the anomalous behavior of the electrical field vertical component (Ez) was observed as U-shaped oscillations every 5-30 s due to the electrical charge excitation and relaxation from the compression of quartz-containing rock. The first approximation showed that the analysis of magnetotelluric (MT) monitoring data could help identify medium- and short-term precursors of seismic events. [ABSTRACT FROM AUTHOR]

This paper describes the behavior of several seismic precursors prior to the 2016–2019 activation in an area of a complex geodynamic setting at the boundary of the Pacific, North American, and Eurasian plates. We used an integrated approach to combine identified precursors with a view to getting more accurate locations of possible rupture zones of future large earthquakes. The precursors include quiescence based on the RTL parameter and the "Z-function", variations in the slope of the earthquake recurrence graph (γ-value), and the areas of seismic ruptures dS. For the first time in Kamchatka, we analyze anomalies in the parameter dS interpreted as seismic activations to show the presence of a precursory component before the onset of the foreshock activation. Examples include increases in the values of that parameter before events that were the largest for the areas where they occurred: the Near-Islands Aleutian earthquake of July 17, 2017, Mw = 7.8 and the Uglovoe Podnyatie earthquake of December 20, 2018, Mw = 7.3. The overall extent of the anomalous area, which still exists and includes consecutive quiescence and foreshock phases, is ~900 km, which creates conditions for possible occurrence of a new great earthquake in the junction zone of the three plates with a magnitude that can exceed whatever has been recorded in the region so far. [ABSTRACT FROM AUTHOR]

The Chuya earthquake of 2003 exerted an appreciable influence on the seismicity of the entire Altai. This paper presents data on variations in the Altai seismicity from 2003 to 2021. It is shown that earthquakes of the first half-year after the major earthquake of 2003 had their rupture zones in the epicentral zone, while the other Altai structures were aseismic. After 2009 we saw changes both in the near zone that encompasses geological structures that were adjacent to the epicenter (with distances of 60‒80 km from the mainshock epicenter), such as the Aigulak, Kurai, South Chuisky and North Chuisky mountain ranges, and in the far zone at distances of 250‒450 km from the epicenter and in different directions from it. The Aigulak earthquake of 2019 gave rise to an aftershock process that displaced the center of Altai seismicity to the eponymous mountain range. There are no data on large earthquakes during the historical period for many Altai structures which have been activated following the Chuya earthquake, either from seismological or from paleo-geological evidence. One could explain the evolution of seismicity around the rupture zone of the Chuya earthquake in space, and with time delays of some years, invoking the influence of a large earthquake on a medium involving plasticity. We know of nonlinear models that hold promise for future research concerning the influence of large earthquakes on the evolution of seismicity in geological media. [ABSTRACT FROM AUTHOR]

This paper presents a causal relationship between thoron anomaly and earthquakes along the Indo-Burman subduction line. A 15 min cycle thoron data was generated at Mizoram University, Aizawl, Mizoram (India) between January, 2019 and December, 2019 for correlation with earthquakes. All earthquakes within 150 km from the monitoring station were correlated with an average precursory time of 7 ± 5 days. The empirical mode decomposition (EMD) based Hilbert–Huang transform (HHT) analysis shows that thoron anomaly of the monitoring station specifically responds to those earthquakes along the subduction line and the region was seismically active. [ABSTRACT FROM AUTHOR]

Seismic monitoring matters both for research and for populations living in areas of seismic hazard; however, it comes with a cost that is not fully affordable for developing countries. Compared to classical approaches with very quiet sites and high-quality instrumentation, it is therefore worth investigating low-cost seismic networks and how well they perform at detecting and characterizing seismicity. We analyze 1 year of seismic data from an educational seismology network in Nepal, create our own earthquake catalog, and compare it to the publicly available national observatory catalog. We find that despite the noisier seismic station sites, the overall results are comparable and all the main features relevant for seismicity are found. We present quantitative analyses of locations, magnitudes and their frequency distribution in our catalog, as well as differences with the observatory catalog. Differences between the two catalogs primarily stem from the respective network geometries and their coverage, as well as daytime noise level differences. We conclude that if properly planned and installed, low-cost seismic networks are a viable, feasible and significant complement to monitor seismic activity. [ABSTRACT FROM AUTHOR]

Accurately imaging seismogenic structures is crucial for seismic hazard assessment. This is especially important around the deformation front (DF) region off SW Taiwan, where seismic potential is high but the fault structure and seismic activity are still poorly understood. Here, we present a comprehensive delineation of seismogenic structures along the onshore and offshore DF of SW Taiwan, utilizing hypocenter relocations and first-motion focal mechanism solutions from January 1991 to March 2019. Five distinctive seismogenic structures are delineated. Particularly, the energetic seismic activity initialled after the 2017 Mw5.3 Tainan earthquake and migrated northeastward along the western side of the DF. The offshore trace of the DF could serve as a boundary delimiting the seismic activity driven by the flexural stress of the subducted Eurasia Plate to the west of the DF. This observation could constrain the magnitude estimation of future earthquakes offshore SW Taiwan. Meanwhile, the areas with higher seismic moment release are located near the DF rather than known faults, indicating that the DF may dominate the seismic moment release. However, further study is warranted into the intricate relationship among seismic strain variation, the structure of DF, and seismic activity to further understand the seismic potential. Our first-motion focal mechanism solutions show that several earthquakes in SW Taiwan were characterized by P-axis orientations parallel to the strike of the Taiwan orogeny. Those events are preferably explained by the lateral compression induced by the ongoing collision between the Eurasia and Philippine Sea plates. Key Points: The deformation front has high seismic potential but seismogenic structure remains unclear. The deformation front confined seismic activity and released relatively large seismic moments. The role of the deformation front must be considered in seismic hazard assessment. [ABSTRACT FROM AUTHOR]

We systematically investigate the identification and statistical characteristics of foreshock sequences in the North–South seismic belt (21 ~ 43°N, 97 ~ 107°E), which is the test area of China under the "Collaboratory for the Study of Earthquake Predictability (CSEP)," so as to provide data support for foreshock probability forecasting and monitoring deployment. In this paper, we use a stochastic declustering method based on a space–time epidemic-type aftershock sequence (ETAS) model to fit the real catalogs in the North–South seismic belt, and separate each catalog into stochastic versions of family trees, so as to identify the foreshock sequences and analyze their space–time characteristics and statistical characteristics. The results show that the proportion of foreshock sequences of ML ≥ 3.0 earthquakes in the North–South seismic belt is not significantly higher than that in other regions of the world (New Zealand, Southern California) without considering the difference in cutoff magnitude. The number of foreshock sequences in the North–South seismic belt displays obvious regional differences, with the number in the middle section distinctly lower and in the south section distinctly higher, while accounting for nearly 50% in all earthquake sequences except for a few areas. The foreshock sequence duration is mostly one to one hundred days, without displaying obvious correlation between the duration of sequences and foreshock sequences and latitude. The background earthquakes have a high b value, approximately 0.89. The b value of foreshock sequences, especially foreshock sequences in the strict sense, is low, approximately 0.72. The b value of aftershock sequences is the lowest, approximately 0.69. The duration of foreshocks in most earthquake sequences is lower than that of aftershocks, especially in sequences with large numbers of events. Meanwhile, sequences that last for more than 1 year have shorter foreshock sequences and longer aftershock sequences. [ABSTRACT FROM AUTHOR]

The Mw 7.8 earthquake that struck Kahramanmaras on February 6, 2023, caused significant damage to hydrocarbon and water transmission lines due to permanent ground deformations. Explosions occurred in the Kahramanmaras–Gaziantep Natural Gas transmission pipeline causing disruption of gas in the cities of Gaziantep and Hatay Fault Displacement Hazard. Water transmission pipelines were also damaged due to extreme fault offsets. This paper presents the findings from the earthquake affected zones. Particular attention was given to the performance of the 2600 mm diameter Duzbag–Gaziantep water transmission pipeline due to three reported challenges: (#1) The behavior of the pipe in the Duzbag tunnel, (#2) The pipe bend behavior at the fault crossing, and (#3) The pull-out of the pipe at valve room. Based on field observations, extreme damage forms at pipes were presented. A three-dimensional nonlinear numerical analysis was performed to simulate the observed damage of the reoriented water pipe at the fault crossing for Case #2. The nonlinear finite element model was able to capture the complex nature of the post-yield behavior of steel pipe as well as the damage locations along the pipe and their sequence of occurrences. As a mitigation measure for new pipes, the need for using flexible connections at critical crossings was highlighted. For existing pipes, the importance of developing secondary (by-pass) lines was emphasized. [ABSTRACT FROM AUTHOR]

Earthquakes (mainshocks) trigger sequences of aftershocks, the frequency of which diminishes following a power-law decay, while the spatial domain of these aftershocks extends logarithmically over time. The delineation of the aftershock zone can be modulated by variables beyond the magnitude of the mainshock, encompassing the location of the fault (whether the fault is at a plate boundary), the depth at which the event occurs, and the prevailing local stress conditions. Here, we evaluate the expansion rate of aftershock zones by analyzing earthquakes of magnitude-7 class in the vicinity of the Japanese archipelago. Prior studies have offered approximate assessments of expansion rates; however, our approach involves the utilization of a straightforward algorithm for the automated estimation of this metric, facilitating the compilation of a catalog. Across the dataset, no pronounced correlations were discerned between the expansion rate and other examined parameters. Yet, an inverse relationship is identified between the expansion rate and the b value of aftershocks for mainshocks occurring at plate boundaries. This observation suggests that the expansion rate of aftershock zones predominantly mirrors the stress field following the mainshock. Such a pattern is not detected in mainshocks occurring within the plate's interior. While the expansion rate of aftershock zones is likely influenced by various factors, aftershock zones may expand more rapidly with higher differential stress in areas surrounding hypocenters of major interplate earthquakes of magnitude 8 or 9. [ABSTRACT FROM AUTHOR]

We calculated stress drops for 2875 small intraslab earthquakes at intermediate depths beneath Tohoku, Japan. We applied an S-coda-wave spectral ratio method to almost 900,000 event pairs. Detailed velocity values for the oceanic crust (OC) were adopted from previous observational studies. The median stress drops in the OC are about half those in the oceanic mantle (OM). The median stress drop for earthquakes in the OC decreases from depths of 70 to 120 km and increases from 120 to 170 km. Our preferred interpretation is that the rigidity in the OC decreases and then increases with depth due to combined effects of the dehydration associated with the eclogite formation and the increasing temperature with depth. These depth variations are consistent with results of a similar study beneath Hokkaido. The median stress drops in the oceanic plate beneath Tohoku are generally smaller than those beneath Hokkaido. Previous studies imaging the seismic structure at shallow depths and b-value analyses of intraslab earthquakes indicate that the near-trench region of the oceanic plate off Tohoku is more hydrated than that off Hokkaido. Taken together, these results suggest that differences in the degree of hydration of the oceanic plate in the near-trench regions could produce the different behaviors of stress drops of intermediate-depth earthquakes observed in Tohoku and Hokkaido. [ABSTRACT FROM AUTHOR]

The mid-eastern segment of the Qilianshan fault zone (QLF) on the northeastern margin of the Qinghai–Tibet Plateau is considered one of the key seismic hazard areas. The Zhangye Ms5.0 earthquake and Menyuan Ms6.9 earthquake are the two Ms ≥ 5.0 earthquakes in recent years. The spatio-temporal evolution of Rn across the fault before the two Ms ≥ 5.0 earthquakes were explored by combining a solid seismogenic model and numerical simulation results in this study. The results demonstrates the spatial distribution of Rn concentration intensity varies over time, indicating the evolving characteristics of fracture zone activity. The time-series variation characteristics are closely related the Zhangye Ms5.0 earthquake and Menyuan Ms6.9 earthquake. Overall, in the seismic source area and surrounding medium area of Zhangye Ms5.0 earthquake, the soil gas Rn anomaly across faults characterized by a turning upward trend after continuous decline. The closer to the source area, the more obvious the upward trend. For Menyuan Ms6.9 earthquake, the survey line (HT1) located in the main fracture zone of the earthquake and the survey line (HT7,30km from the epicenter) closer to the epicenter also showed a similar trend, while the other measurement lines in far-field exhibit declining trend before the Menyuan Ms6.9 earthquake. Therefore, the continuous decline trend of soil gas may be crucial information for medium-term earthquake preparation in the seismogenic zone, and the trend of turning upward after continuous decline is a significant signal of short-term seismogenic event in far-field. This research could improve the understanding of the anomalous features of soil gas precursors and tracking the active sections of the fault. According to the model, the earthquake area canseismic source area, the surrounding medium area be divided into three sections: the seismic source area, the surrounding medium area, and the fracture fragmentation area. [ABSTRACT FROM AUTHOR]

In this study, we developed a three-dimensional (3D) (Qp) P-wave attenuation model of the uppermost crust (0–10 km depth) of the Koyna-Warna region (India). The inversion of attenuation operator (t*) is used to deduce a 3D Qp attenuation model using simul2000 code by assuming that t* is independent of frequency. A total of 276 earthquakes (1.0 ≤ ML ≤ 3.5) were used for this study, those providing 2045 t* values. The t* values are determined by fitting the observed P-wave amplitude spectrum with the theoretical spectrum by assuming an ω2 source model using a nonlinear least squares spectral-fitting algorithm. The tomography model shows the low Qp anomalies (~ 200–350) at shallow depth (0–3 km) that could be related to fracturing and cracks. The Qp value gradually increases with depth due to the closure of cracks and fractures as pressure increases from the lithostatic load. The high Qp (~ 500–600) are found in the intense seismic activity zone at 5–7 km depth where majority of the earthquakes were generated corresponds to the brittle crust and well correlated to higher Vp (~ 5.5–6.0 km/s) reported previously in the study area. We inferred that the high Qp is well correlated to seismicity likely associated with the dry to partially saturated rocks, which playing a vital role in the genesis of earthquakes in the study area. [ABSTRACT FROM AUTHOR]

Changing thermal regime is one of the key mechanisms driving seismogenic behaviors at cold megathrusts, but it is difficult to interpret warm subduction zones such as Vanuatu for the temperatures are higher than that accommodates shallow brittle failures. We construct a 3-D thermomechanical model to clarify the thermal structure that controls tectonic seismicity in Vanuatu and predict a warm circumstance associated with abundant seismicity. Results reveal a heterogeneous slab ranging from 300 °C to over 900 °C from the Moho to subvolcanic depth. The subduction seismicity corresponds well to the plate interface where dynamic thermal dehydration is focused. The transformation from hydrated basalts to eclogites along the slab facilitates the occurrence of intense earthquakes and slips. Multistage mineralogical metamorphism affects the dynamic stability of megathrusts and favors the generation of active interplate large events. Therefore, slab thermal dehydration plays a greater role than slab temperature condition in influencing the subduction earthquake distribution in warm subduction systems. [ABSTRACT FROM AUTHOR]

Nowadays, development projects are becoming so rapid in many developing countries worldwide. The study of interest focuses on Cairo–Suez District, which represents the most important location in Egypt for major infrastructure projects and urbanization expansion. Consequently, it is very important to reduce the hazards surrounding this area from natural disasters, so all information that supports geo-environmental hazards assessment is importantly needed. The Gabal Ataqa area has socioeconomic importance as it is considered the industrial zone in the national project for developing the northern part of the Gulf of Suez. The situation of Gabal Ataqa area for being rich with numerous geological structures, and its socioeconomic importance calls the need for the delineation of the subsurface structural features in this area using the appropriate method. The geological framework has recognized all Quaternary faults in the Gabal Ataqa area as they are exposed to the surface, at the same time, no seismic reflection data has been acquired in the Gabal Ataqa area. Accordingly, the shallow seismic reflection method is applied in the Gabal Ataqa area to detect the Quaternary faults that are not exposed to the surface and also to detect any subsurface features that may cause construction problems, such as water-wet sands, sabkhas, and limestone cavities. Three lines of 2D seismic profiles are acquired in the study area. After applying seismic data processing and interpretation, two Quaternary faults have been recognized in the first and third lines. The location of the first seismic line has been chosen to be between two historic earthquake events, increasing the probability that the sources causing these two events will be located on the newly recognized quaternary fault. A dim spot has been recognized in the second seismic line at a depth of 50 m, which may indicate the presence of a groundwater aquifer or wet sandstone layer. Based on these results, changing the industrial zone place to another side to be away from the area of the three seismic lines is highly recommended. [ABSTRACT FROM AUTHOR]

Slow earthquakes occur at deep and shallow plate boundaries along the Nankai Trough. Deep slow earthquakes are continuously distributed along the 30–40 km depth contours of the upper surface of the subducted Philippine Sea Plate. In contrast, shallow slow earthquakes occur in limited regions: Hyuga-nada, off Cape Muroto, and southeast off the Kii Peninsula. This review provides an overview of the up-to-date seismological, geodetic, geological, and experimental results in the shallow Nankai area for a unified understanding of the spot-like occurrence of shallow slow earthquakes. Shallow slow earthquakes tend to be distributed in transitional regions between the frictionally locked and stably sliding zones on the plate boundary. Based on geological and experimental studies, the lithology of incoming sediments and their friction coefficients can be variable along the Nankai Trough. Laboratory friction experiments revealed that sediments under shallow plate boundary conditions often exhibit positive (a − b) values, while negative (a − b) is possible via several processes. Subducted seamounts create complex fracture networks and stress shadows in their surrounding areas; however, not all subducted seamounts are related to shallow slow earthquake activities. This incomplete correlation suggests that alternative factors are required to explain the spot-like distribution of shallow slow earthquakes in the Nankai subduction zone. High pore fluid pressure conditions around shallow slow earthquake zones were interpreted based on seismological structural studies. In addition, ambient noise monitoring revealed temporal changes in seismic velocity structures associated with shallow slow earthquake migrations. This result suggests a close link between pore fluid migration and shallow slow earthquake episodes. Because transient changes in pore fluid pressure can lead to various slip behaviors, the episodic migration of pore fluid around the plate boundary could promote shallow slow earthquake activity along the Nankai Trough. [ABSTRACT FROM AUTHOR]

The magnetotelluric (MT) investigation carried out in Koyna Seismogenic Zone (KSZ), an intra-plate earthquake region in Western India, along an E–W profile brings out moderately conductive (~ 700–1000 Ωm) near vertical features within the very high resistive (> 20,000 Ωm) granite/granite-gneiss basement. Occurrences of these anomalous moderate conductors are corroborated with sensitivity analysis. The alignment of earthquake hypocenters along the resistive–conductive boundary signifies the moderate conductor as basement fault. The conversion of resistivity values to the ratio of seismic P- to S-wave velocity (vp/vs) suggests that the moderate conductivity of the fault zone (as compared to the surrounding basement) appears due to the presence of fluid in the fault zone. Geophysical evidences reveal ~ 2.5–3.6 vol% fluid in the fault zone with ~ 1.8–2.6% interconnected porosity, which migrates along the structural boundary and invades the mechanically strong basement to nucleate the brittle failure within it. The present study proposes two mechanisms for the seismicity in the Koyna region. First: the meteoric water circulation due to the loading–unloading of nearby Koyna reservoir acts as potential fluid source for this triggered seismicity, which has also been suggested by previous studies. Second: the fluid circulation due to a deep-seated source. The present MT study brings out a conductive feature below 20 km depth which is thought to be emerged due to the dehydration of amphibole bearing rocks. The fluid generated from dehydration might act as a probable source to the triggered seismicity; since the conductive feature has a linkage to the upper crust. [ABSTRACT FROM AUTHOR]

This study focuses on the empirical assessment of the control period TC for intermediate-depth earthquakes. A ground motion database of about 700 recordings from 25 intermediate-depth seismic events occurring in the Vrancea seismic zone in Romania as well as in other sources in the world is used in the study. A simple empirical model is proposed for the evaluation of the control period TC. The largest part of the variability of the proposed empirical model can be attributed to the intra-event component. The analysis of the residuals has shown no significant bias due to the different tectonic regimes of the earthquakes in the database. A comparison between the seismic hazard results in terms of TC computed using the proposed empirical model and from spectral accelerations according to the procedure from the proposed Eurocode 8 draft is performed for several case study sites in Romania. The probabilistic seismic hazard assessment shows that the control periods TC computed in this study are much larger than the ones obtained using the approach from the proposed Eurocode 8 draft revision and larger, as well, than the TC values proposed in the current version of the Romanian seismic design code P100-1/2013. The study also shows that for Romania, a solution for the seismic hazard zonation is to perform the analysis of Sα according to the provisions from the proposed Eurocode 8 draft and to evaluate the control period TC using an empirical model. [ABSTRACT FROM AUTHOR]

To date, multiple ground-motion prediction equations (GMPEs) for the significant duration (DS) of shallow crustal earthquakes have been proposed, but there are few GMPEs for subduction intraslab and interface earthquakes in Japan, and corresponding spatial correlation models have not been published. To address this issue, we first select ground-motion records with moment magnitude 4 ≤ Mw ≤ 9, rupture distance Rrup ≤ 300 km, and peak ground acceleration ≥ 10 gal based on the K-NET and KiK-net databases. Then, for intraslab and interface earthquakes in the subduction zone, based on previous works, the traditional source duration term is simplified, a depth term is added, and new GMPEs for DS of earthquakes in the subduction zone in Japan are developed. The rationality and reliability of the prediction model proposed in this study are verified by residual analysis and comparison with the previous models. Finally, according to the intra-event residuals, a spatial correlation model of DS is established by using a semivariogram and exponential model. The results show that DS of subduction interface earthquakes is larger than that of subduction intraslab earthquakes on the whole, but the spatial correlation coefficient of subduction interface earthquakes decreases more slowly with increasing separation distance than that of subduction intraslab earthquakes, and the significant duration of the spatial correlation is related to site effects and path effects. The results provide a reference for the development of GMPEs based on nonergodic assumptions, regional seismic hazard analysis and loss assessment. [ABSTRACT FROM AUTHOR]

In the Three Gorges reservoir region, central China, seismic activity increased substantially after the reservoir impoundment in 2003 which continues till date. Previous studies show that these are reservoir-triggered earthquakes and various factors are responsible for the increase in seismic activity after the reservoir impoundment. However, these studies do not provide a comprehensive assessment of influence of reservoir water level variations on spatiotemporal distribution of earthquakes. In this study, we statistically analyze the influence of the water level variations on the increased seismic activity in the reservoir region for the period from May 2003 to April 2020, using the power spectrum and singular spectrum techniques. Our statistical analyses confirm the influence of long-term variations in the water level time series on the occurrence of earthquakes after the reservoir impoundment. The analysis also indicates a positive role of annual reservoir water level fluctuations in the total seismicity of the region. Depending on the cluster patterns and relationship with faults, the earthquakes of the Three Gorges reservoir region are divided into three seismic zones (A, B, and C). For zone C, both the power spectrum and singular spectrum analyses confirm the strong periodic influence of reservoir water level variations on the earthquakes. Increase in seismicity of zone B is only in the initial period but not in the later stages of water impoundment and our statistical analyses indicate that the seismicity of this zone is not directly related to the annual reservoir water level variations. This confirms the conjecture in the earlier studies that the seismicity of this zone is related to the collapse of coal mines present in the area in the initial stages of reservoir impoundment. For zone A, our statistical analyses do not show strong influence of the annual reservoir water level variations on the occurrence of earthquakes. We suggest that this is due to the contribution of various other factors along with reservoir impoundment in the occurrence of earthquakes in this zone, as also opined in some earlier studies. [ABSTRACT FROM AUTHOR]

Numerous studies have confirmed that electromagnetic disturbances before earthquakes can be observed by satellites. In this study, we use the C-value method that includes the acoustic whistle signature; pre-seismic ionospheric electromagnetic disturbance signals were acquired based on the CSES-01 satellite electric field data, and the maximum value of C in the earthquake preparation zones increased continuously from 2.0 three days before the earthquake and reached a maximum weight of 3.0 on the day of the earthquake, after the earthquake, it gradually decreased and recovered to about 2.0; its the C values fluctuated between −2 and 3, it is different from the C values range −2–12 of the previous seismic case study using the DEMETER satellite, which may be related to the orbital altitude and revisit period of the satellite. Then, the C values were normalized, and the time series analysis of the obtained θ values were done, and the results showed that: In the pregnant zone, the background variation of the disturbance amplitude θ is within 2σ, and the maximum disturbance amplitude of θ starts to increase gradually from the seventh period (one period of 5 days, i.e., 35–39 days before the earthquake), it reached 2σ by the fourth pre-seismic cycle (20–24 days before the earthquake), and then dropped sharply to about 1.5σ in the third pre-seismic cycle (15–19 days before the earthquake), after two cycles of increase, the θ over the epicenter reached a maximum of 2.1σ at the time of the earthquake (combining the time of the earthquake and the satellite flight characteristics, the epicenter period is defined as January 25–January 29, 2020, and this defines the study time period line), and the θ decreases to within 2 times the standard range after the earthquake; The negative value of the disturbance amplitude θ in the central region of the pregnant seismic zone during the earthquake shows the transient energy release process. Through comparison, the θ values obtained by normalization based on the C-value method takes into account the variation of the background field, and the result can better reflect the energy change of the ionospheric field before the earthquakes. [ABSTRACT FROM AUTHOR]

Abstract—The geomechanical modeling of the stress-strain dynamics before the 2019 M = 7.1 Ridgecrest earthquake, Southern California, revealed an alternating pattern of maximum displacement anomalies that develop around the ends of the future rupture, simulating the process of "swinging" in the epicentral zone of the earthquake. These results, together with the existing theoretical concepts of crustal block structure with block interaction, are used to build a "swing" geomechanical model based on the stick-slip phenomenon in a three-block configuration. The parameters of the model are related to the rheological properties of the Earth's crust in the area of destruction of the bridging isthmus (a patch), which determines the source size of the seismic event. [ABSTRACT FROM AUTHOR]

Designing a structure to resist earthquakes by targeting an explicit failure risk has been a key research topic over the past two decades. In this article, a risk-targeted design approach is developed for circular reinforced concrete bridge piers, based on a probabilistic optimization procedure aimed at minimising the design resisting moment at the pier base. In order to reduce the computational effort, a surrogate model is developed to describe the influence of two key design parameter (i.e., the pier diameter and the longitudinal reinforcement ratio) on the structural behaviour and performance. The proposed approach is applied in a case study for Italy for target mean annual frequencies of failure selected according to European codes using a probabilistic seismic hazard assessment for average spectral acceleration across a wide range of structural periods. The variation in the design parameters across Italy is considerable because of the large variation in seismic hazard. It is found that in areas of low seismic hazard the level of seismic design required is near the minimum allowed by Eurocode 8 in terms of reinforcement ratio. In areas of the highest seismic hazard much higher reinforcement ratios and pier diameters are required to meet the risk targets. If both pier diameter and longitudinal reinforcement ratios are considered as design parameters then the optimisation procedure may mean adjacent sites have significant different pairs of these parameters as the target can be reached in multiple ways. This problem can be solved by fixing one parameter and optimising the other. [ABSTRACT FROM AUTHOR]

Trench sediments such as pelagic clay or terrigenous turbidites have long been invoked to explain the seismogenic behavior of the megathrust fault (i.e., décollement). Recent numerous studies suggest that slow earthquakes may be associated with huge megathrust earthquake; however, controls on the slow earthquake occurrence remain poorly understood. We investigate seismic reflection data along the Nankai Trough subduction zone to understand the correlations between the spatial distribution of the broad turbidites and along-strike variations in shallow slow earthquakes and slip-deficit rates. This report presents a unique map of regional distribution of the three discrete Miocene turbidites that underthrust apparently along the décollement beneath the Nankai accretionary prism. A comparison of distributions of the Nankai underthrust turbidites, shallow slow earthquakes, and slip-deficit rates enables us to infer that the underthrust turbidites may cause primarily low pore-fluid overpressures and high effective vertical stresses across the décollement, leading to potentially inhibiting the slow earthquake occurrence. Our findings provide a new insight into potential role of the underthrust turbidites for shallow slow earthquakes at subduction zone. [ABSTRACT FROM AUTHOR]

Vulnerability assessment of an urban area to earthquake hazards is the requirement to attaining sustainable urban resilience. Quetta city is the capital of the province of Balochistan surrounded by mountains with the existence of many active faults. The main objective of the current study was to assess the earthquake vulnerability in Quetta valley. A total of 400 households were selected for the primary household survey. A simple random sampling technique is employed using proportionate allocation method because of the heterogeneity of the area in terms of population. Secondary data was taken from the Geological Survey of Pakistan (GSP), the Pakistan Bureau of Statistics (PBS), and the United States Geological Survey (USGS). Analytical Hierarchal Process (AHP) & Weighted Linear Combination (WLC) methods are used to identify earthquake vulnerability. The results of the study reveal that the Northwestern and Southeastern parts of Quetta are seismically vulnerable to earthquake hazard; its geology coupled with the human dimension indicates a more disastrous future events. Results of the composite earthquake vulnerability show that seven out of thirteen Zones of Quetta city are highly vulnerable to all four components of vulnerability. Four Zones have a medium level of vulnerability and only two Zones are considered low earthquake vulnerable Zones in the study area. The topmost influential factors that make Quetta city highly earthquake-vulnerable are the soil type (0.45), peak ground acceleration (0.34), proximity to the hospitals and fire service stations (0.22, 0.21), elderly population (0.22) and fault lines (0.21) as shown in Fig. 12. This research study has significant implications for urban planners and provides a risk reduction platform in order to reduce future earthquake losses and make Quetta city more resilient and sustainable. [ABSTRACT FROM AUTHOR]

Abstract—The role of relatively weak earthquakes as an instrument to study the medium, including during strong earthquakes, is studied. The spatial structure of the attenuation field of several seismic regions (the Garm geodynamic test site in Tajikistan; Altai; the Caucasus; Eastern Anatolia; the Western Tien Shan) and epicentral regions of a number of strong earthquakes is considered, and the confinement of deep seismicity to this structure is analyzed. It is shown that the attenuation field estimated from short-period coda of weak earthquakes in seismic regions is inhomogeneous, consisting of blocks with high Q-factor and weakened zones with high attenuation. It is noted that the deep earthquakes have an uneven spatial distribution, which correlates with the block structure: there are more deep earthquakes in the weakened zones than in the high-Q blocks. Examples of variations in the deep seismicity activity in the weakened zones are presented. Deep seismic activity varies over time, increasing before strong earthquakes. Facts are presented that point to the existence of a correlation between the Earth's rotation rate and the intensity of deep seismicity. Examples of activation of weak seismicity in the form of seismic swarms (series of weak earthquakes localized in space and time) in connection with strong events are shown. A characteristic feature of the swarm sequences is that the earthquake localization regions are isometric in plan and elongated vertically. As a rule, these regions coincide with the weakened zones of strong S-wave attenuation. Intense localized seismicity confined to one-dimensional domains is most likely to be associated with highly conductive channels acting as pathways for deep fluid migration. Activation of swarm seismicity is driven by active migration of deep fluids and increasing fluid saturation of the weakened zones. Fluids, in turn, are catalysts of the processes leading to rock strength degradation and block destruction in the epicentral zones. In this case, clusters of seismic swarm sequences can be considered as local seismogenic zones. The formation of compact clusters of weak seismicity, isometric in plan and nearly vertical in the cross section, is also quite frequently observed outside the epicentral zones of strong earthquakes. Such zones may simply be indicators of the seismotectonic situation in the region as a whole. It is believed that a sharp change in the dynamics of atmospheric pressure during the preparation of a strong earthquake, detected by weather stations located in such areas is a consequence of the intergeospheric interaction between the lithosphere and the atmosphere. One of the main mechanisms of the anomalous behavior of atmospheric pressure during strong seismic events appears to be deep degassing, which is most active in the weakened zones. The mechanisms by which deep degassing affects the outer geospheres are still a matter of debate. [ABSTRACT FROM AUTHOR]

Detailed and accurate historical earthquake disaster data are an important basis for understanding the characteristics of earthquake disaster losses and for conducting research on earthquake disaster prevention strategies and post-earthquake emergency rescue work. Due to different project scopes and discrepancies in data accuracy, the currently available databases may contain errors such as missing data or data with low accuracies. In this study, we developed the Mainland China Composite Earthquake causing Casualties Database (MCCEC-DAT), which contains 252 historical earthquake records that span from 1966 to 2021. The database contains earthquake attribute information (earthquake time, location, epicenter latitude and longitude, focal depth, epicentral intensity, etc.), loss information (number of deaths and injuries, building damage ratio, economic loss, cause of death, etc.), and socioeconomic data (population, population density, area of each zone of seismic intensity, mortality rate, etc.). This database also contains the lethality levels generated by this study. These levels are the result of the quantitative evaluation of the overall characteristic levels of the earthquake area. Furthermore, this metric permits the direct comparison of different spatial locations. Based on the results of the statistical analysis, this work shows that the distribution of historical earthquakes in mainland China has obvious spatial and temporal characteristics. Events are mainly distributed throughout the southwest region, and the magnitudes of those events are relatively diverse. The mortality rate is significantly correlated with the building damage ratio and the lethality level. The lethality level can not only facilitate an improved understanding of the comprehensive level of historical earthquake regions, but this metric also provides a quantitative foundation for the comparative analysis of earthquakes between different regions. Furthermore, the database can also provide a foundation for future research, such as research into assessing the loss from earthquake disasters. [ABSTRACT FROM AUTHOR]

This article investigates the properties of small-scale fluctuations of the probability density for measurements of the X, Y, and Z-components of the Earth's magnetic field that were carried out both in a seismically active region and in an area with a complete absence of seismic activity. In the first case, a much greater intensity of the occurrence of statistical phenomena considered as earthquake precursors was revealed. At an interval of several days before the earthquake with a magnitude of 5.3 in Metsavan (Armenia), whose epicenter was located near the magnetic variation station in a seismically active region, a sharp increase in the frequency of these phenomena was found. This effect was absent in the seismically quiet region. [ABSTRACT FROM AUTHOR]