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The article focuses on the study titled "Energy radiated by seismic events of different scales and geneses" by G.G. Kocharyan. Topics discussed include role of factors like Radiated Energy (Es), Seismic Moment (M0) and Differential Magnitude in seismic events of different scales and geneses; study claiming such significant conclusions which relies on the analysis of the empirical data; and differences between the high frequency and low frequency parts of the radiation spectrum.

This paper is focused on study of the geomagnetic field variation response caused by a series of earthquakes with magnitudes of Mw = 7.5–7.8 in Turkey on February 6, 2023. The initial data include high-precision observations of the geomagnetic field with a one-second sampling rate recorded at magnetic observatories in Russia and neighboring countries from middle to high latitudes. The paper analyzes the morphology of the geomagnetic signal, its amplitude-frequency characteristics, pulses in the rate of change and delays of the geomagnetic field response to earthquakes with magnitudes Mw = 7–8 depending on the distance to the source. The results suggest that the geomagnetic effect is detected best in the rate of change recordings, reaching anomalous amplitudes of 10 nT/s. The signal delay ranges from 221 to 592 s depending on the magnetic field component and the distance to the epicenter, which is in the range from 765 to 2650 km for the selected observatories. [ABSTRACT FROM AUTHOR]

In this paper, a scalable end-to-end tree boosting system called XGBoost has been applied for predicting the magnitude of an earthquake from the early part of earthquake waveform data. This model uses the features extracted from the early P wave phase of the records as an input. The model's effectiveness has been verified by using data on earthquakes occurring in the Eurasian plate of Japan Islands from 1996 to 2021. Feature engineering has given 29 new features identified from the early P wave phase of the record, which show a high correlation with the magnitude of an earthquake. The comparison of predicted and actual magnitude shows that a trained XGboost model, which uses a single input record for magnitude prediction, gives an average prediction error of 0.004 ± 0.57 for earthquakes in the test dataset. In contrast, the average prediction error of –1.1 ± 0.80 and –0.65 ± 0.69 has been obtained for the magnitude estimated from conventional τc and Pd methods using the same test dataset. It is further seen that the average predicted magnitude of a single earthquake of magnitude 4.5 and 6.1 (MJMA) obtained by using multiple nearfield records using XGBoost model is 4.58 ± 0.33 and 6.32 ± 0.29, which is close to the actual magnitude of the earthquake. The results presented in this paper clearly show that the structured data can be effectively used by complex machine learning or deep learning models to predict earthquake magnitude from single or multiple records. [ABSTRACT FROM AUTHOR]

Liquefaction occurs when the ground experiences intense shaking due to seismic activities, causing water-saturated soils or loosely packed sediments near the surface to weaken and behave like a liquid. The present paper has reviewed and investigated the liquefaction around tunnels due to any seismic event that may occur during the tunnel's lifetime. To effectively prevent soil liquefaction around the tunnel, it is crucial to analyze both the acceleration response of the tunnel and the soil motion that results from liquefaction. This paper examines the geotechnical engineering aspects of such liquefactions and discusses analytic techniques to mitigate their effects. Also, the response of tunnel displacement under different magnitudes of earthquakes has been discussed. Different mitigation methods are explored in response to the damages caused by the liquefaction of soil due to earthquakes. Case studies of this problem that occurred in different nations were analyzed as well, amidst which are tunnel disasters in Turkey, Syria, China, Italy, Japan, India, and the USA. These instances demonstrate the terrible repercussions of liquefaction, such as building collapse, road network destruction, and surface and subsurface structure deterioration. By reviewing these instances, major patterns and trends in liquefaction-induced damages emerge, giving valuable insights for future mitigation and engineering practices. This review serves as a valuable resource for engineers and researchers involved in tunnel design, construction, and maintenance. This review paper addresses the dangers associated with liquefaction in soils and highlights the need for robust design considerations and appropriate construction techniques to mitigate potential damages. [ABSTRACT FROM AUTHOR]

On September 18, 2022, an earthquake with a local magnitude (ML) 6.8 struck the southern part of Longitudinal Valley in southeastern Taiwan, resulting in the collapse and damage of many engineering structures. A field reconnaissance was conducted at the selected sites that experienced building and bridge damages and is presented in this paper. The focus is on geotechnical problems such as strong ground motion, ground rupture, soil liquefaction, and their influence on engineering structures. Strong motions of up to 0.6 g were induced, with similar intensity in the vertical and horizontal components near the epicenter. Widespread ground rupture traces were observed along the officially recognized active faults, inducing offsets up to tens of centimeters. Soil liquefaction was also noticed in this region, mainly on the river flood plain and characterized as gravel layer. The possible influence of these observed geotechnical characteristics on the damage pattern or failure mode of buildings, bridges, embankments, and levees was discussed and interpreted insightfully. The perspectives presented in this paper may serve as a reference to disaster prevention and mitigation in future events. [ABSTRACT FROM AUTHOR]

The existence of several magnitude scales in the compiled earthquake catalogs of a specific region has made the development of regional relations connecting magnitude scales a necessity, especially for creating a homogeneous seismic catalog in which all magnitudes should be converted to a preferred magnitude scale. To consistently estimate all magnitude ranges and avoid the saturation problem for large earthquakes, the preference is always given to the moment magnitude Mw scale, wherein the most complete and reliable catalog used worldwide is the Global Centroid Moment Tensor (GCMT). However, to our knowledge, no study has yielded regional (in Algeria) relationships for converting different magnitudes to the moment magnitude (Mw,GCMT). The main reason is typically due to the lack of data pairs of different magnitude scales with Mw (GCMT). To overcome this issue, in this research paper, the moment magnitudes data used for northern Algeria (the area bounded by 32° to 39° N and 3° W to 10° E) have been taken principally from the GCMT catalog and enhanced with the European–Mediterranean Regional Centroid Moment Tensor catalogs RCMT and ZUR-CMT. Regarding this latter, it has been demonstrated in the literature that for the Mediterranean regions, a minor correction should be addressed before merging its data with the GCMT and RCMT catalogs, which are perfectly correlated. To accomplish this task, the magnitude scales tested against Mw are the surface wave magnitude, MS, and the body wave magnitude mb issued from the international seismological sources of ISC and NEIC for the same boundaries. As long as the earthquake magnitudes, in general, are affected by errors of comparable size, the best and most reliable regression method that considers the errors in both dependent and independent variables for linear conversion problems is the General Orthogonal Regression, which is adopted and applied herein to develop the regional relations. [ABSTRACT FROM AUTHOR]

Joshimath has received much attention for its massive ground subsidence at the beginning of the year. Rapid urbanization and its unique geographical location may have been one of the factors contributing to the occurrence of this geological disaster. In high mountain valley areas, the complex occurrence mechanism and diverse disaster patterns of geological hazards highlight the inadequacy of manual monitoring. To address this problem, the inversion of deformation of the Joshimath surface in multiple directions can be achieved by multidimensional InSAR techniques. Therefore, in this paper, the multidimensional SBAS-InSAR technique was used to process the lift-track Sentinel-1 data from 2020 to 2023 to obtain the two-dimensional vertical and horizontal deformation rates and time series characteristics of the Joshimath ground surface. To discover the causes of deformation and its correlation with anthropogenic activities and natural disasters by analyzing the spatial and temporal evolution of surface deformation. The results show that the area with the largest cumulative deformation is located in the northeastern part of the town, with a maximum cumulative subsidence of 271.2 mm and a cumulative horizontal movement of 336.5 mm. The spatial distribution of surface deformation is based on the lower part of the hill and develops towards the upper part of the hill, showing a trend of expansion from the bottom to the top. The temporal evolution is divided into two phases: gentle to rapid, and it is tentatively concluded that the decisive factor that caused the significant change in the rate of surface deformation and the early onset of the geological subsidence hazard was triggered by the 4.7 magnitude earthquake that struck near the town on 11 September 2021. [ABSTRACT FROM AUTHOR]

Because of the scarcity of recorded seismic ground motions from Vrancea intermediate-depth source that can be used in designing a structure, engineers are bound to use scaled, artificial, or simulated accelerograms. Out of these options, the first two might incompletely account for the phenomena that may appear. Although complicated, simulated accelerograms provide one of the best options for defining the seismic demand in engineering design, but further research is needed to adapt the simulation methods to the source, path, and site-specific characteristics. As some parameters used in simulations were not addressed yet specifically for the Vrancea-intermediate seismic source, the specific path duration is investigated in this paper. Using a database with the recorded ground motions from March 4, 1977, August 30, 1986, May 30 and May 31, 1990, October 27, 2004 Vrancea earthquakes (the only five recorded earthquakes with moment magnitudes at least equal to 6), the path and magnitude dependent duration specific to Vrancea intermediate-depth seismic source to be used in the stochastic simulation is developed. [ABSTRACT FROM AUTHOR]

As part of studies on the search for earthquake precursors, the authors have conducted an experiment on long-term precision monitoring of variations in the resistivity of the Earth's crust in a highly seismic region of Tajikistan. The primary data of this experiment can be considered a special type of VES profile, in which, instead of a linear coordinate, the sounding date changes from picket to picket. When processing precision monitoring data, it is necessary to solve the inverse VES problem with the highest possible accuracy. VES curve inversion programs commonly used in electric exploration do not allow this. The authors have previously developed a special method for regularizing the residual functional, which suppresses the effect of resistivity buildup, due to which the error in reconstructing the resistivity of rocks for profiles with a strong seasonal variation in resistivity is reduced by an order of magnitude. However, in some cases, the regularized algorithm strongly biases estimation of the amplitude of the seasonal resistivity variation in the lower layers of the section. In this paper, the operation of the proposed algorithm is tested in detail for nine model profiles simulating a real geoelectric section. The considered profiles differed in the characteristics of the seasonal variability of resistivity in the lower layers of the section (the phase and amplitude of seasonal effects varied). It is shown that resistivity buildup is effectively suppressed in all cases. For each model profile, the error in solving the inverse problem is estimated. The effect of a biased estimate of the amplitude of seasonal variation is studied. It is shown that in most cases, analysis of the solution makes it possible to reveal the presence of such distortions and qualitatively assess their character. It is also shown that for profile options supposedly closest to the experimental profile, the estimates have minimal bias. For all profiles, the ratio of the average and maximum errors in calculating the resistivity in different layers to the residual in the solution to the inverse problem was evaluated. This makes it possible to evaluate the actual error of the reconstructed resistivity values knowing only the fitting residual. The paper also studied the possible effect of increasing the accuracy in solving the inverse problem in the case of preliminary decomposition of the apparent resistivity curves into seasonal and flicker noise components. It is shown that for small fitting residuals, the results change insignificantly. According to the results obtained, the error in reconstructing the aperiodic (flicker noise) component of resistivity variations in the lower layers of the considered section can be decreased to 0.4%. The accuracy in reconstructing the seasonal component of resistivity variations depends on the amplitude and phase of seasonal effects in the model profile. For the considered profiles, the error varies from 1 to 2%. [ABSTRACT FROM AUTHOR]

Among the most important questions that await an answer in seismology, perhaps one is whether there is a correlation between the magnitudes of two successive seismic events. The answer to this question is considered of fundamental importance given the potential effect in forecasting models, such as Epidemic Type Aftershock Sequence models. After a meta-analysis of 29 papers, we speculate that given the lack of studies carried out with realistic physical models and given the possible bias due to the lack of events recorded in the experimental seismic catalogs, important improvements are necessary on both fronts to be sure to provide a statistically relevant answer. [ABSTRACT FROM AUTHOR]

A vast amount of analogue seismograms recorded between the end of the nineteenth century and late twentieth century are often inaccessible for seismological research since they are not available as digital time series. This manuscript describes freely available software, DigitSeis, that takes a digital image of an analogue seismic record and returns waveforms either as a function of their x-y position on the image or as time–amplitude information. The overall structure and approach of the software are provided along with how they have evolved over different versions. The effectiveness of the software is demonstrated with three examples. The first example is a long-period east–west seismogram recorded at the Harvard Seismographic Observatory on photographic paper in May of 1938, which contains signals associated with a magnitude 7.7 earthquake that occurred off the coast of Northern Ibaraki, Japan. The second example is an analysis of a 35-mm microfilm copy of the short-period vertical seismogram recorded at Tucson, Arizona, on July 16, 1945, that shows blast signals from the first nuclear bomb detonation. The final example uses a 70 mm microfiche image of a long-period north–south seismogram recorded at College, Alaska in December of 1966, which shows a pair of earthquakes with nearly identical waveforms. The software is, by no means, perfect, and discussion of its limitations such as the compatibility with pen- and Develocorder-type seismograms is included, as well as comments about challenges of incorporating machine learning into the digitization process. [ABSTRACT FROM AUTHOR]

This paper analyzed the strong motion characteristics based on 86 three-component strong motion records of the MW 6.6 Luding earthquake. Additionally, the factors that influence the variation in ground motion for three earthquakes with similar magnitude in Sichuan Province were investigated. The analysis result indicates a strong correlation between the observed ground motion parameters and the distribution of published Modified Mercalli Intensity. The residual analysis reveals that the spectral accelerations at periods 0.1–10.0 s are amplified to 0.0798–0.3057 times the mean level in the rupture forward direction and weakened to 0.0738–0.2831 times the mean level in the rupture backward direction. The maximum pulse direction recorded by the 51LDJ station is N6°E, aligning with the vertical fault direction. The velocity pulses has distinct bidirectional pulses in the waveforms, with a PGV of 37.0 cm/s. The source effect of the strike-slip MW 6.6 Luding and MW 6.5 Jiuzhaigou earthquakes on ground motion is relatively less significant compared to the average level of mainshocks in southwest China. However, the thrust-fault MW 6.7 Lushan earthquake exhibits a stronger source effect on ground motion during short and medium periods, but a weaker source effect during long periods when compared to the average level. The anelastic attenuation of the Longmenshan, Xianshuihe, and Huya fault zones in Sichuan exhibits significant regional variation and periodic correlation. This phenomenon is closely linked to the regional tectonic background variations and the heterogeneity of crustal structure within the area. [ABSTRACT FROM AUTHOR]

The Indian Himalayan region is frequently experiencing climate change-induced landslides. Thus, landslide susceptibility assessment assumes greater significance for lessening the impact of a landslide hazard. This paper makes an attempt to assess landslide susceptibility in Shimla district of the northwest Indian Himalayan region. It examined the effectiveness of random forest (RF), multilayer perceptron (MLP), sequential minimal optimization regression (SMOreg) and bagging ensemble (B-RF, B-SMOreg, B-MLP) models. A landslide inventory map comprising 1052 locations of past landslide occurrences was classified into training (70%) and testing (30%) datasets. The site-specific influencing factors were selected by employing a multicollinearity test. The relationship between past landslide occurrences and influencing factors was established using the frequency ratio method. The effectiveness of machine learning models was verified through performance assessors. The landslide susceptibility maps were validated by the area under the receiver operating characteristic curves (ROC-AUC), accuracy, precision, recall and F1-score. The key performance metrics and map validation demonstrated that the B-RF model (correlation coefficient: 0.988, mean absolute error: 0.010, root mean square error: 0.058, relative absolute error: 2.964, ROC-AUC: 0.947, accuracy: 0.778, precision: 0.819, recall: 0.917 and F-1 score: 0.865) outperformed the single classifiers and other bagging ensemble models for landslide susceptibility. The results show that the largest area was found under the very high susceptibility zone (33.87%), followed by the low (27.30%), high (20.68%) and moderate (18.16%) susceptibility zones. The factors, namely average annual rainfall, slope, lithology, soil texture and earthquake magnitude have been identified as the influencing factors for very high landslide susceptibility. Soil texture, lineament density and elevation have been attributed to high and moderate susceptibility. Thus, the study calls for devising suitable landslide mitigation measures in the study area. Structural measures, an immediate response system, community participation and coordination among stakeholders may help lessen the detrimental impact of landslides. The findings from this study could aid decision-makers in mitigating future catastrophes and devising suitable strategies in other geographical regions with similar geological characteristics. [ABSTRACT FROM AUTHOR]

This paper addresses how residents can safely access shelters from their buildings. Firstly, we investigated Xiaying Village, a typical community with severe buildings damage at the epicentre of the Ms5.0 magnitude earthquake in Tonghai that occurred on August 13, 2018, and found that the injured residents when escaping resulted from the damage to masonry buildings. Secondly, a probabilistic approach combining response spectrum and allowable maximum acceleration is proposed to estimate the damage risk of masonry buildings with inadequate seismic performance in old communities. Thirdly, three models are proposed to assess the risk of the escape path, which include all scenarios of the escape of residents to shelters. Finally, an accessibility analysis of the paths that residents may choose to escape to the shelter is presented. The results of the community escape case study in the Tonghai earthquake show that the probabilistic approach to estimating the escape risk is feasible, and the number of damaged buildings in the escape path dictates the accessibility of residents to the shelter. The proposed method is important for guiding old community residents to escape when a strong earthquake strikes, and it is an effective way to improve community disaster resilience. [ABSTRACT FROM AUTHOR]

Predicting the magnitude of induced earthquakes by underground injection is a critical strategy for risk assessment. This paper proposes the application of three machine learning techniques—support vector machine, probabilistic neural network, and AdaBoost algorithm—to predict the magnitude of the largest injection-induced earthquake (M) within a predetermined period. These machine learning techniques are used to model the relationships between ten input parameters—six seismicity indicators and four inputs related to injection wells—and earthquake magnitude classes (M < 3, 3 ≤ M < 4, and M ≥ 4). Models are applied to the earthquake and injection data for the Central Oklahoma region in the USA, and their input data are balanced using the data-level approach. The performance of each model is measured using the average recall of earthquake magnitude classes. The results show that balancing the training data improves the performance of the models, and the magnitude of induced earthquakes depends on the injection volume in the nine months before the earthquake prediction period. The parametric analysis of each model's input reveals that induced earthquake magnitudes are more likely to occur when there are shorter distances between the bottom of injection wells and the crystalline basement. Among the investigated models, the support vector machine model trained on the data balanced using synthetic minority oversampling technique performed best by predicting an average of 72% of earthquake magnitude classes. Overall, the findings of this study will allow for predicting the magnitude of induced earthquakes and the development of an early warning system for policymakers and residents living in areas prone to injection-induced earthquakes. [ABSTRACT FROM AUTHOR]

In regions of infrequent but potentially damaging seismicity, modern earthquake inventories may be insufficient to provide inputs to seismic hazard analyses (i.e., fault locations and magnitude–frequency relations). As a result, analysis of paleoseismic evidence, such as coseismic landsliding, is commonly used to help elucidate the seismic record, thereby reducing seismic hazard uncertainty. However, while paleolandslides have been investigated widely, existing inverse-analysis techniques (i.e., to constrain the causative earthquake magnitude and/or ground motions) have several shortcomings, namely, they (i) require the location of the causative earthquake to be known, (ii) provide only a lower-bound estimate of seismic parameters, and (iii) are deterministic in nature. Accordingly, this paper proposes a flexible inversion framework that probabilistically constrains seismic source parameters from regional paleolandslide evidence. The outputs of this framework are (i) a geospatial likelihood surface that constrains the location of fault rupture and (ii) a probability distribution of the rupture magnitude. Simulated paleolandslide studies are performed on modern earthquakes with known parameters. These examples demonstrate the framework's provocative potential as well as important lessons for implementation. The proposed framework has the potential to extract new insights from relic landslide evidence in seismic zones worldwide. [ABSTRACT FROM AUTHOR]

The timely and accurate assessment of casualties is the key for and basis of emergency rescue work after an earthquake. In this paper, through exponential fitting of historical seismic data, an evaluation model of death based on the building destruction ratio is proposed. Through the analysis of historical seismic data, we propose the concept of an anti-lethal level and construct the corresponding coefficient. We use factors such as earthquake magnitude, intensity, and occurrence time, the population density, and the anti-lethal level in the region as correction factors for the predicted number of casualties and build a model for evaluating the number of casualties based on coefficient correction. The evaluation results are relatively accurate; the R2 index of the proposed model is 0.8768, whereas the R2 of the two comparison models selected in this paper is 0.619 and 0.4603, respectively. The accuracy of the proposed model results is much higher than that of the other models, which illustrates the effectiveness of the model presented in this paper. It also indicates that the model proposed in this paper can provide a scientific basis and data support for earthquake emergency rescue work. [ABSTRACT FROM AUTHOR]

The Bucaramanga seismic nest has the highest concentration in volume of intermediate depth seismic events with light and moderate magnitudes (Mb > 4.8) worldwide. Despite the nest depth (Zhypo ≥ 100 km), these events play a crucial role in the seismic hazard assessment for several cities in northern South America (NoSAm), particularly those situated close to their epicenters. Moreover, these earthquakes are widely felt across the country, even hundreds of kilometers away from the nest. This paper assesses the performance of commonly used subduction intraslab Ground Motion Models (GMMs) in predicting the updated nest database gathered and processed by the Colombian Geological Survey. This analysis confirms the necessity of a partially non-ergodic ground motion model for estimating the spectral accelerations produced by Bucaramanga nest earthquakes in northern South America. The GMM presented herein is the first model developed specifically for seismic nests in the region and is conceived as a regionalization of the recent NGA-Sub Abrahamson and Gülerce (Earthq Spectra 38(4):2638−2681, 2022) GMM. Additionally, we provide estimates of the variance components at both the earthquake and station levels and compare the developed GMM with the spectral accelerations recorded for typical earthquakes, for the highest magnitude earthquake in the database, and for a recent Bucaramanga nest earthquake having a moment magnitude over 5. [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]

With the rapid development of network technology, research on the emotional tendencies of online disasters has increasingly played a significant role in responding to disaster public opinion events. This paper collected data from microblogs and selects three relatively large earthquakes that occurred in Sichuan in 2022 as research samples, namely the Lushan earthquake that occurred on June 1, the Malkang earthquake that occurred on June 10, and the Luding earthquake that occurred on September 5. By calling the E-Trans emotional analysis model, the emotional tendency values were obtained. Using Python language and a time–frequency of 15 min, the original content posted by microblog users within 24 h after the earthquake was analyzed for emotional tendencies, and research conclusions were drawn on the characteristics of emotional tendencies in earthquake disasters and related factors. The results show that the emotional tendencies of the three earthquakes conform to the "Three·Three" emotional tendency model for disasters, and the emotional tendency values in the three periods show a significant marginal diminishing effect. Changes in emotional tendencies during earthquake disasters are mainly related to the magnitude of the earthquake, the number of aftershocks, issues that the public is more concerned about on microblogs, and earthquake prevention and mitigation department microblog promotions. This study can provide a reference for post-disaster emergency response and network public opinion guidance for earthquake prevention and mitigation. [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]

On 14 November 2021, doublet earthquakes with magnitude 6.1 and 6.3 occurred near Fin town, in the north region of the Persian Gulf, Iran. This paper analysed the ground motion characteristics of records obtained during the 2021 Fin doublet earthquakes. The different features of these events in the far and near distances have been compared with an update local ground motion prediction equation proposed for Iran. The peak ground acceleration (PGA) and spectral acceleration of records at the 2021 Fin doublet earthquakes are also compared with the 2012 Ahar–Varzaghan doublet events. Analysis of ground motions illustrated that the attenuation rate for the PGA and the spectral accelerations at a short period of 0.2 s is higher than Ahar–Varzaghan events. Several ground motions parameters, including PGA values and spectral acceleration, Fourier spectra, significant duration and Arias intensity obtained at two nearest stations (Siahoo and Varzaghan) in these two doublet events, are discussed. Comparison of spectral accelerations showed that the amplitude of spectral accelerations takes large values in short periods (high frequencies) at the Siahoo station. A large difference is observed between significant duration values obtained at Varzaghan and Siahoo stations which could be explained by the presence of a pulse in the records of Varzaghan station. The results also showed that the spectral level observed at the Sihao station in short periods is higher than the level of the seismic design code, which can be a reason for the high damage to low-rise buildings. [ABSTRACT FROM AUTHOR]

Many applications related to ground-motion studies and engineering seismology benefit from the opportunity to easily download large dataset of earthquake recordings with different magnitudes. In such applications, it is important to have a reliable seismic characterization of the stations to introduce appropriate correction factors for including site amplification. Generally, seismic networks in Europe describe the site properties of a station through geophysical or geological reports, but often ad-hoc field surveys are missing and the characterization is done using indirect proxy. It is then necessary to evaluate the quality of a seismic characterization, accounting for the available site information, the measurements procedure and the reliability of the applied methods to obtain the site parameters.In this paper, we propose a strategy to evaluate the quality of site characterization, to be included in the station metadata. The idea is that a station with a good site characterization should have a larger ranking with respect to one with poor or incomplete information. The proposed quality metric includes the computation of three indices, which take into account the reliability of the available site indicators, their number and importance, together with their consistency defined through scatter plots for each single pair of indicators. For this purpose, we consider the seven indicators identified as most relevant in a companion paper (Cultrera et al. 2021): fundamental resonance frequency, shear-wave velocity profile, time-averaged shear-wave velocity over the first 30 m, depth of both seismological and engineering bedrock, surface geology and soil class. [ABSTRACT FROM AUTHOR]

The seismicity of Romania is mostly represented by earthquakes produced by the Vrancea seismic source with intermediate depth events (3 shocks/century with magnitude MW greater than 7.0). The seismic activity in Romania also includes crustal earthquakes. The crustal seismicity is more scattered and moderate compared to the intermediate-depth one. A stable and automatic method has been implemented in the real-time data acquisition and processing system ANTELOPE to estimate the seismic moment, the moment magnitude and the corner frequency of events recorded by the velocity sensors, using spectral analysis applied to S waves. The main goals are the independent estimation of the seismic moment and the common characterization for all events recorded by the National Seismic Network. The main target of this paper is represented by the fast estimation of moment magnitude MW and ground motion parameters that are derived using Gallo et al. (Bull Earthquake Eng 12:185–202, 2014) methodology and their validation with other magnitude determination algorithms existing at the National Institute for Earth Physics (NIEP). To test this new methodology, we have analyzed 331 seismic events, most of them being automaticaly located, and afterwards added a new, manually processed solution for events with ML ≥ 4.5, to obtain a larger interval of magnitudes. [ABSTRACT FROM AUTHOR]

Abstract —This work presents the results of GPS observations (2003–2020) carried out in PrimorskyKrai (aka the Primorie) and Khabarovsk Krai in southeastern Russia. The objectives of our study were to obtain displacement velocities, to test the relation of current velocities with seismicity, with the specific features of the geological structure of the Primorie, and to study the rheological parameters of the crust and asthenosphere at the continental margin. This paper analyzes the results of measurements made in the Primorie at the Central Sikhote-Alin fault. The study includes the effects of the Tohoku-Oki earthquake in Japan with magnitude М = 9 which occurred on March 11, 2011. The zone of coseismic and postseismic displacements extends to a distance of over 1000 km from the epicenter. The postseismic decay of the long-term horizontal and vertical displacements allow us to estimate the relaxation time for the elastic-viscous model. With the decay times of 4 to 8 years, the viscosity of the lower layer in the two-layer rheological model is estimated at 8 × 1018–3 × 1019 Pa s. Using the bending model of the Earth's surface and the bottom of the Sea of Japan, we estimated the thickness of the elastic upper part of the Earth's crust in the continent–ocean contact zone at 20–25 km. [ABSTRACT FROM AUTHOR]

In this paper, a subsequence time-series clustering algorithm is proposed to identify the strongly coupled aftershocks sequences and Poissonian background activity from earthquake catalogs of active regions. The proposed method considers the inter-event time statistics between the successive pair of events for characterizing the nature of temporal sequences and observing their relevance with earthquake epicenters and magnitude information simultaneously. This approach categorizes the long-earthquake time series into the finite meaningful temporal sequences and then applies the clustering mechanism to the selective sequences. The proposed approach is built on two phases: (1) a Gaussian kernel-based density estimation for finding the optimal subsequence of given earthquake time-series, and (2) inter-event time ( Δ t ) and distance-based observation of each subsequence for checking the presence of highly correlated aftershock sequences (hot-spots) in it. The existence of aftershocks is determined based on the coefficient of variation (COV). A sliding temporal window on Δ t with earthquake's magnitude M is applied on the selective subsequence to filter out the presence of time-correlated events and make the meaningful time stationary Poissonian subsequences. This proposed approach is applied to the regional Sumatra-Andaman (2000–2021) and worldwide ISC-GEM (2000–2016) earthquake catalog. Simulation results indicate that meaningful subsequences (background events) can be modeled by a homogeneous Poisson process after achieving a linear cumulative rate and time-independent λ in the exponential distribution of Δ t . The relations C O V a (T) > C O V o (T) > (C O V b (T) ≈ 1) and C O V a (d) > C O V o (d) > C O V b (d) are achieved for both studied catalogs. Comparative analysis justifies the competitive performance of the proposed approach to the state-of-art approaches and recently introduced methods. [ABSTRACT FROM AUTHOR]

Groningen gas field, which is being exploited for more than five decades, has been experiencing shallow and small magnitude earthquakes that cause limited structural damage to the building inventory in the region. These earthquakes are recorded in a relatively small area with multiple recording networks, which constitute a dense strong ground motion sensor grid, providing valuable insight into the characteristics of the motions produced by some 2500+ small faults at 3 km depth. The particularities of the Groningen soil, as well as the high seismic vulnerability of the structural inventory, render the Groningen earthquake problem complex, although the magnitudes experienced so far did not exceed 3.6ML. This paper is an attempt to compare the Groningen earthquake records to records from other induced seismicity and natural seismic events with similar characteristics in terms of magnitude, epicentral distance and depth, for identifying systematic differences in terms of component-to-component variability. In order to achieve that, a total of 1831 recording suites (i.e. couples of horizontal components) are used. 201 of these are Groningen records, 1112 are from other induced seismicity events to geothermal, waste water injection and hydraulic fracturing activities, while 517 are from natural earthquakes. The high polarity of the Groningen records, that is previously reported in the literature and represented as component-to-component variability in risk models, is the main focus of this paper. The component-to-component variability constitutes an important step when implementing ground motion models (GMMs) in risk assessment studies. In this study, in agreement with previous research, the component-to-component variances show that the Groningen induced seismicity events present stronger polarity than the other records used for comparison. The other induced seismicity recordings also show high component-to-component variances as compared to the natural events records, but the main difference is that their variances start decreasing in medium-to-long (i.e. above 0.6 s) periods while the variances steadily increase in the case of Groningen records. Furthermore, it is also observed that the component-to-component variances increase considerably when the rotated-to-max-PGA angle, explained in the paper, is used for defining the two horizontal components instead of using components as-recorded or rotated perpendicular to the station back azimuth. A modification to the component-to-component variance model of Groningen GMM v5 has also been proposed in this study for taking into account the orientation of the structural plan directions in respect to the ground motion component directions. [ABSTRACT FROM AUTHOR]

The goal of many earthquake engineering analyses is to ensure that a structure can withstand a given level of ground shaking while maintaining a desired level of performance. But there is a great deal of uncertainty about the numerous factors that impact the level of ground shaking. probabilistic seismic hazard analyses (PSHA) aim to quantify these uncertainties and combine them to produce an explicit description of the distribution of future shaking that may occur at a site. Among others, the distribution of the magnitudes is required by PSHA. This paper presents a new approach to estimate both the tail distribution of earthquake magnitudes and the tail distribution of the maximum earthquake magnitude over a year. This approach uses extreme value models based on Poisson process. The main innovations consist of combining the use of the generalized Pareto distribution (GPD) to model the tail distribution of earthquake magnitudes and the exact relation leading to the tail distribution of the annual maximum earthquake magnitude. We also propose a statistical inference that takes into account the growing incompleteness of the data in earlier times, which enables us to use as much available data as we can. This paper also provides a sensitivity analysis, which quantifies the robustness of the results with respect to two types of uncertainty: the statistical uncertainty due to the limited number of data used for the statistical inference and the uncertainty related to the determination of the complete observation periods of time by the seismologists. We detail validation tests to check the main assumptions underlying the probabilistic model: the Poisson occurrences of earthquakes and the GPD behavior of the tail distribution. The methodology is applied to an area located in the south of France, which provides estimates of some extreme quantiles of the annual maximum earthquake magnitude. [ABSTRACT FROM AUTHOR]

Seismic risk analyses derive from earthquake catalogs a recurrence relation linking earthquake activity rate to magnitude. The most widely employed model is the log-linear Gutenberg–Richter relation (Gutenberg and Richter, Science, 83, 183–185, 1936; Gutenberg and Richter, Bulletin of the Seismological Society of America, 46(3), 105–145, 1945), with modifications at larger magnitudes (Cosentino et al., Bulletin of the Seismological Society of America, 67, 1615–1623, 1977; Kijko and Sellevoll, Bulletin of the Seismological Society of America, 79(3), 644–654, 1989; Page, Bulletin of the Seismological Society of America, 58, 1131–1168, 1968; Pisarenko and Sornette, Pure and Applied Geophysics, 160, 2343–2364, 2003; Turcotte, Physics of the Earth and Planetary Interiors, 111, 275–293, 1999). This relation leads to exponentially distributed magnitudes truncated to a maximum magnitude, a priori fixed under geophysical considerations. In this paper, we assume seismic events occur according to a Poisson distribution, but we propose to model the tail distribution of magnitudes with a generalized Pareto distribution (GPD). The GPD parameters are estimated with a maximum likelihood procedure. This GPD-based model gives rise to a new recurrence model that differs from the Gutenberg–Richter Law. It eliminates the need to introduce a maximum magnitude in the analysis that is difficult to determine. This paper details the expression of the estimators of the GPD parameters and the asymptotic normal distribution when the shape parameter ξ > - 1 . This asymptotic distribution yields confidence intervals for all parameters. The GPD parameter estimators account for the following features of the data set: (a) seismic events are collected on periods whose span depends on their magnitudes; (b) magnitudes are imprecisely known: each magnitude is supposed to uniformly belong to an interval of length 0.5. Our new model is estimated from information coming from the FCAT17 catalog. This catalog collects seismic events from the Alps region in France. We conduct an uncertainty analysis, and we quantify the impact of estimation uncertainty on the recurrence model. [ABSTRACT FROM AUTHOR]

In recent years, there is a significant increase in research combining social media data for disaster warning and damage assessment. When natural disasters occur, social media data can also contain rumors, which not only reduce the accuracy of assessment but also have a very negative social impact. In this paper, a multi-feature fusion neural network with attention mechanism is proposed for rumor detection, which makes the attempt to integrate user, textual and propagation features in one united framework. Specifically, a Bidirectional Long Short-Term Memory Network (Bi-LSTM) is applied to extract user and textual features and a Graph Convolutional Neural Network (GCN) is employed to extract the high-order propagation features. In addition, both the complementary and alignment relationships between different features are considered to achieve better fusion. It shows that our method can detect rumors effectively and perform better than previous methods on the Weibo dataset. To validate the effectiveness of our model, rumor detection is conducted in the social media data collected from Typhoon Lekima on Aug 10th–14th 2019 in China, the earthquake of magnitude 6.8 on Sep 5th–9th, 2022 in Sichuan, China, the wildfire on Aug 15th–26th, 2022 in Chongqing, China. Results show that: (1) the proposed method performs well in rumor detection in disaster; (2) rumors often appear along with hot topics; (3) rumors express much negative sentiment; (4) rumor propagation networks have tighter structure and deeper propagation depth. (5) rumors account for a relatively small percentage of social media data in disaster, which means that most social media data is credible. [ABSTRACT FROM AUTHOR]

Abstract—This is our second paper concerning the study of earthquakes in Eastern Anatolia based on the information reported in the periodicals of the Russian Empire. We have made a systematic search of all the available Armenian, Georgian, and Russian language newspapers. This resulted in the first inventory of descriptions of the macroseismic effects from the June 29/July 12, 1900 earthquake, which were observed in 14 populated localities. Using these data, we determined the location of the epicenter and the magnitude of the earthquake. The macroseismic magnitude 5.9 precisely coincides with the instrumental magnitude reported in (Ambraseys and Finkel, 1987), while the epicenter location differs by 25 km. The epicenter location estimated in this work seems to be more reliable because its determination is based only on the original descriptions of the macroseismic effect. [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]

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]

Quickly determining earthquake size by extracting information after P-wave arrival is a critical issue for earthquake early warning systems. However, early warning parameters are often calculated using a fixed-length (3–5 s) P-wave time window for rapid magnitude estimation. In this paper, we directly investigate magnitude-scaling relationships within the available P-wave time window (APTW, defined as the window period starting from the trigger time of the P wave and ending at the arrival of the S wave) and explore a new real-time magnitude estimation approach (the APTW method). The results of an offline application demonstrate the good performance of the APTW method in terms of the stability of magnitude estimation for small to moderate earthquakes and improved estimation for large earthquakes. The APTW method can provide estimates earlier, and the estimated magnitudes are more stable. The proposed method of establishing magnitude relationships could provide an alternative choice for magnitude estimation in earthquake early warning systems. [ABSTRACT FROM AUTHOR]

Probabilistic seismic hazard assessment (PSHA), including a site-specific amplification study, is crucial to evaluate site-specific spectra of soil sites to better understand the behavioural patterns of the soils under earthquake excitation. This paper represents the results of the PSHA for Assam state, located in the highest seismic zone of India ever delineated to date. In that sense, the study area is divided into ten areal zones concerning seismicity source modelling to represent the seismo-genesis of the Assam state in detail. The earthquake recurrence parameters of each zone are obtained from Gutenberg–Richter (G–R) recurrence relation with updated homogenized and de-clustered earthquake catalogue from 1735 up to 2021. Earthquakes with magnitude greater than 4 (M > 4) are considered using eight attenuation relationships for continental active shallow crust region, subduction zone and intraplate region. Hazard curves are obtained using a logic tree structure thus minimizing the epistemic uncertainty. The peak ground acceleration (PGA) value obtained at the rock outcrop of the Assam state for 10, 5, 2, and 0.5% probability of exceedance in 50 years with return periods such as 475, 975, 2475, and 9975 years lies between 0.24 and 0.34 g, 0.3 and 0.44 g, 0.42 and 0.59 g, and 0.56 and 0.91 g, respectively. The estimated PGA value at rock outcrop level is comparatively higher than that reported in the codal provisions. Site-specific response spectra at bedrock level (Vs = 1100 m/s) for major cities (Jorhat, Tezpur, Silchar, Dibrugarh, Guwahati, Nagaon) of Assam state have been proposed for different earthquake return periods of 475,2475, and 9975 years. Finally, site amplification study is performed for Guwahati city and surface level 5% damped response spectra with PGA of 0.696 and 0.924 g are obtained for earthquake a return period of 2475 and 9975 years, respectively. [ABSTRACT FROM AUTHOR]

On the 26th of November 2019, an earthquake of moment magnitude 6.4 struck the northwest region of Albania as the result of thrust faulting near the convergent boundary of the Africa and Eurasia plates causing widespread damage to buildings in the city of Durrës and the surrounding areas. Based on the official data from the national authorities, the earthquake caused 51 casualties and 985 million-euro losses, corresponding to 7.5% of the 2018 gross domestic product. This paper summarises field observations made by the Earthquake Engineering Field Investigation Team (EEFIT) after the event. The paper presents an overview of the seismological aspects of the earthquake together with a brief overview of the damage, official loss statistics and the estimated macro- and socio-economic consequences of the event. In addition, it provides a summary of the observed damage to both recent and historical buildings as well as the description of several case studies to illustrate the characteristic damage patterns observed in the main structural typologies of the Albanian building stock. These observations try to identify possible links between the observed damage patterns and the deficiencies in construction practice and use of inappropriate retrofit techniques for historical assets. As many severe damages were observed on modern buildings, this also allows the identification of some gaps and possible areas of development of the current seismic design code. In the end, the lessons learned from the field survey are resumed. [ABSTRACT FROM AUTHOR]

Nearly half of coal mine disasters in China have been found to occur in clusters or to be accompanied by earthquakes nearby, in which all the disaster types are involved. Stress disturbances seem to exist among mining areas and to be responsible for the observed clustering. The earthquakes accompanied by coal mine disasters may be the vital geophysical evidence for tectonic stress disturbances around mining areas. This paper analyzes all the possible causative factors to demonstrate the authenticity and reliability of the observed phenomena. A quantitative study was performed on the degree of clustering, and space–time distribution curves are obtained. Under the threshold of 100 km, 47% of disasters are involved in cluster series and 372 coal mine disasters accompanied by earthquakes. The majority cluster series lasting for 1–2 days correspond well earthquakes nearby, which are speculated to be related to local stress disturbance. While the minority lasting longer than 4 days correspond well with fatal earthquakes, which are speculated to be related to regional stress disturbance. The cluster series possess multiple properties, such as the area, the distance, the related disasters, etc., and compared with the energy and the magnitude of earthquakes, good correspondences are acquired. It indicates that the cluster series of coal mine disasters and earthquakes are linked with fatal earthquakes and may serve as footprints of regional stress disturbance. Speculations relating to the geological model are made, and five disaster-causing models are examined. To earthquake research and disaster prevention, widely scientific significance is suggested. [ABSTRACT FROM AUTHOR]

In regions that undergo low deformation rates, as is the case for metropolitan France (i.e. the part of France in Europe), the use of historical seismicity, in addition to instrumental data, is necessary when dealing with seismic hazard assessment. This paper presents the strategy adopted to develop a parametric earthquake catalogue using moment magnitude Mw, as the reference magnitude scale to cover both instrumental and historical periods for metropolitan France. Work performed within the framework of the SiHex (SIsmicité de l’HEXagone) (Cara et al. Bull Soc Géol Fr 186:3-19, 2015. doi:10.2113/qssqfbull.186.1.3) and SIGMA (SeIsmic Ground Motion Assessment; EDF-CEA-AREVA-ENEL) projects, respectively on instrumental and historical earthquakes, have been combined to produce the French seismic CATalogue, version 2017 (FCAT-17). The SiHex catalogue is composed of ~40,000 natural earthquakes, for which the hypocentral location and Mw magnitude are given. In the frame of the SIGMA research program, an integrated study has been realized on historical seismicity from intensity prediction equations (IPE) calibration in Mw detailed in Baumont et al. (submitted) companion paper to their application to earthquakes of the SISFRANCE macroseismic database (BRGM, EDF, IRSN), through a dedicated strategy developed by Traversa et al. (Bull Earthq Eng, 2017. doi:10.1007/s10518-017-0178-7) companion paper, to compute their Mw magnitude and depth. Macroseismic data and epicentral location and intensity used both in IPE calibration and inversion process, are those of SISFRANCE without any revision. The inversion process allows the main macroseismic field specificities reported by SISFRANCE to be taken into account with an exploration tree approach. It also allows capturing the epistemic uncertainties associated with macroseismic data and to IPEs selection. For events that exhibit a poorly constrained macroseismic field (mainly old, cross border or off-shore earthquakes), joint inversion of Mw and depth is not possible, and depth needs to be fixed to calculate Mw. Regional a priori depths have been defined for this purpose based on analysis of earthquakes with a well constrained macroseismic field where joint inversion of Mw and depth is possible. As a result, 27% of SISFRANCE earthquake seismological parameters have been jointly inverted and for the other 73% Mw has been calculated assuming a priori depths. The FCAT-17 catalogue is composed of the SIGMA historical parametric catalogue (magnitude range between 3.5 up to 7.0), covering from AD463 to 1965, and of the SiHex instrumental one, extending from 1965 to 2009. Historical part of the catalogue results from an automatic inversion of SISFRANCE data. A quality index is estimated for each historical earthquake according to the way the events are processed. All magnitudes are given in Mw which makes this catalogue directly usable as an input for probabilistic or deterministic seismic hazard studies. Uncertainties on magnitudes and depths are provided for historical earthquakes following calculation scheme presented in Traversa et al. (2017). Uncertainties on magnitudes for instrumental events are from Cara et al. (J Seismol 21:551-565, 2017. doi:10.1007/s10950-016-9617-1). [ABSTRACT FROM AUTHOR]

Earthquake Prediction has become a field of seismology concerned with the specification of time, location, and magnitude of earthquakes to take preventive measures that could help in worst-case scenarios, i.e., destruction of homes and lives. Short Term Earthquakes depends on anomalous events known as precursors that occur before an Earthquake. Precursors are considered a warning before an earthquake. This prediction system uses Earth's Electric Field Signal (EEFS) from Athens, Pyrgos, and Hios. Some examples are Ground Uplifting, Tilting, Emission of Radon Gas, Radio Waves, Magnetic Waves, and Earth's Electric. The EEFS can be considered a precursor to estimate the magnitude and time of a possible earthquake. A minute-by-minute reading of the Earth's Electric Field was taken, and few computations, models like ANN, SVM-ANN, and SVM-KNN, were applied. Few other models were created to estimate the time and magnitude of the earthquake. To discover an ideal model, results are compared without any constraints such as overfitting. The paper presents directions for estimating time and is directing for researchers to analyze in multiple dimensions. [ABSTRACT FROM AUTHOR]

Quantifying the magnitude of an earthquake is very important for long-term and medium-term earthquake prediction, post-earthquake emergency rescue and seismic hazard assessment. Paleo-seismology is the investigation of past earthquakes in the geological record, in particular their location, timing and size. Uncertainties remain in the paleo-earthquake magnitudes determined by traditional surface rupture parameters, especially because most seismic events do not result in surface ruptures or are of less than 0.3 m (M = ~ 6–6.8). To address the problem of magnitude evaluation of earthquakes that did not reveal major dislocations, this paper deals with the methods used to determine the seismic shaking intensity based on the types and forms of soft-sediment deformation structures, including maximum liquefaction distance, thickness of disturbed layer, empirical formulae, and thickness of rapidly deposited sand layer. Then we discuss and analyze these methods in terms of their theoretical basis, advantages and disadvantages, accuracy, applicability and problems. We chose two case studies: first, a typical seismics-related deposit (liquefied layer and disrupted layer) represented by a seismite in the late-Pleistocene Lake Lisan section near Masada in the Dead Sea Basin; and second, the liquefied diapir triggered by an earthquake in the late-Quaternary lacustrine sediments at Luobozhai in the upper reaches of the Minjiang River, East Tibet. The five methods listed above are employed to determine earthquake magnitudes associated with the seismics-related deposit and liquefied diapir, yielding magnitudes of 5.5–6.5 and 6.0–7.0, respectively. The combination of the five methods, provided a new and relatively convenient method for determining seismic shaking, especially in lacustrine sediments. This study can serve as a valid reference for comparing methods of calculating the magnitude of a paleo-earthquake based on surface rupture parameters, and provides a better understanding of the long-term seismic activity and risk in tectonically active regions. [ABSTRACT FROM AUTHOR]

The advent of novel technologies revealed that other geophysical signals than those directly related to fault motion could be used to probe the state of deformation of the Earth's crust. Electromagnetic signals belonging to this category have been increasingly investigated in the last decade in association to natural earthquakes and laboratory rock fractures. These studies are hampered by the lack of continuous recordings and a systematic mathematical processing of large data sets. Indeed, electromagnetic signals exhibit characteristic patterns on a specific frequency band (the very low frequency, VLF) that correlate uniquely with the paroxistic rupture of rocks specimens under uniaxial laboratory tests and were also detected in the atmosphere, in association to moderate magnitude earthquakes. The similarity of laboratory and atmospheric VLF offers an unique opportunity to study the relation between VLF and rock deformation on at least two different scales and to enlarge the dataset by combining laboratory and atmospheric data. In this paper we show that the enlarged VLF dataset can be successfully used, with a neural network approach based on LSTM neural networks to investigate the potential of the VLF spectrum in classifying rock rupture precursors both in nature and in the laboratory. The proposed approach lays foundation to the automatic detection of interesting VLF patterns for monitoring deformations in the seismically active Earth's crust. [ABSTRACT FROM AUTHOR]

The changes in groundwater level in coral islands are more common than those in inland areas. In this paper, a series of shaking table tests were performed to investigate the influence of the groundwater level on the seismic response of a coral sand foundation–superstructure system. The responses of excess pore pressure, acceleration, displacement and bending moment of the model structure were measured and analysed in detail. The results illustrate that owing to the rise in the groundwater level, the natural frequency of the coral ground drops, while the damping ratio increases; in addition, the rising groundwater level has a softening effect on the model ground. Moreover, the excess pore pressure ratios of coral sands increase with rising groundwater level, and the increase in the ratios significantly grows with increasing earthquake strength. The amplification factors of the soil–structure acceleration response decrease with the increase in the groundwater level, regardless of whether the ground motion is weak or strong. Furthermore, both the settlement and horizontal displacements of the model structure increase when the groundwater level rises. In terms of the bending moment, the rise in the groundwater level will reduce the response of the column bending moment irrespective of the earthquake strength. [ABSTRACT FROM AUTHOR]

Monitoring precursory decline in groundwater radon at the Antung hot spring is a useful means of forecasting the magnitude and precursor time of local disastrous earthquakes. With the help of a case study in southeastern Taiwan, this paper demonstrates the effect of tectonic setting in the subduction zone on the correlation between radon decline, precursory time and earthquake magnitude. Given a radon-monitoring site located near the plate boundary in the tectonic setting of advanced arc-continental collision, the observed radon decline and precursory time prior to the earthquakes in the tectonic setting of initial arc-continental collision are smaller than those observed prior to the earthquakes occurring on the plate boundary in the tectonic setting of advanced arc-continental collision. In the advanced arc-continental collision state, the coupling between the plates is strong and the stress transfer is efficient, whereas in the incipient collision state, the coupling and stress transfer are not as good. It also takes additional time lag and attenuation for the stress transfer from one tectonic setting to the other. This paper presents the difference in the precursory behavior of groundwater radon between earthquakes which occurred in two different tectonic settings: advanced and initial arc-continental collision. [ABSTRACT FROM AUTHOR]

Nowcasting refers to the use of proxy data to estimate the current dynamic state of driven complex systems such as earthquakes, neural networks, or the financial markets. In previous papers, methods to nowcast earthquakes have been presented based on the natural time count of small earthquakes after the last large earthquake in a defined, seismically active geographic region. In this method, a large geographic region is identified in which a local region of interest is embedded. The primary assumption in the method is that the frequency-magnitude statistics of the local region are the same as the frequency-magnitude relation of the large region. The nowcasting technique relies on seismic catalogs that are complete in the sense that all events whose magnitude is larger than a completeness threshold have been detected. For this reason, the previous papers have been limited to nowcasting large earthquakes with magnitudes of approximately M7.5. In this article, we extend the nowcasting method to great global earthquakes of magnitudes as large as M9 by defining the surrounding large region as the entire earth. We then analyze the current hazard of a number of selected "local" regions and rank the regions in terms of current risk of great earthquakes. These great events also present significant hazards for generating mega-tsunamis as well as local damage due to intense shaking. We also perform a sensitivity analysis to establish the reliability of the nowcasts. One of our main results is that the eastern Aleutian Islands, site of the M8.6 earthquake of 1 April 1946, is currently the region most at current risk of a great earthquake larger than M8.0. We finish by presenting comments on the applicability of our methods for anticipating the occurrence of great destructive earthquakes and tsunamis. [ABSTRACT FROM AUTHOR]

In this paper, we determine the location of the hypocenter and the magnitude of the earthquake of September 11/23, 1888 based on macroseismic data published in the Russian periodic in Russian, Armenian, and Georgian languages. Calculations showed that the magnitude of the earthquake was previously significantly underestimated, due to which it was not included in the catalog of strong earthquakes in the Caucasus test region (Shebalin and Tatevossian, 1997). The accuracy of the location of the hypocenter makes it possible to identify the active fault, with which the source of the 1888 earthquake is associated. The earthquake with Mw = 6.6 that occurred almost 100 years later confirms the long-term activity of the Western branch of the East Anatolian fault zone. [ABSTRACT FROM AUTHOR]

Abstract—The paper presents the results of a study showing that anomalies in the seismic regime parameters before earthquakes of various magnitudes occur in stages. The occurrence in stages means the correlation between the times of formation and development of anomalies in various seismic regime parameters. Earthquakes in regions with two general types of tectonics are selected for analysis: in the subduction zone (Kamchatka and Japan) and in the rift zone (Iceland). The selection of regions is primarily based on the availability and quality of regional seismic catalogs. GR b-value and the composite parameter known as the RTL are used as the seismic regime parameters. The detection of spatiotemporal anomalies before the selected earthquakes is based on the known "precursory patterns" of the seismic regime parameters. Comparing the durations of the detected anomalies shows that the anomalies of b-value generally occur earlier than the RTL anomalies. Possible reasons why the anomalies occur in stages are suggested. In the vicinity of the studied earthquakes, a change in the seismogenic rupture concentration parameter within the corresponding seismic cycles is also estimated. Comparing the times at which the detected seismic regime anomalies occur with the values of the seismogenic rupture concentration parameter corresponding to these times shows that the formation of seismic regime anomalies occurs at a stage when the system of seismogenic ruptures accumulated during the seismic cycle has almost reached its critical value. [ABSTRACT FROM AUTHOR]

The Sichuan-Yunnan area is located at the southeastern margin of the Tibetan Plateau, where tectonic movement is strong with deep and large faults distributed in a staggered manner, which results in strong seismic activities and severe earthquake hazards. Since the 21st century, several earthquakes of magnitude 7.0 or above occurred in this region, which have caused huge casualties and economic losses, especially the 2008 Ms8.0 Wenchuan earthquake. At present, earthquake monitoring and source parameter inversion, strong earthquake hazard analysis and disaster assessment are still the focus of seismological researches in the Sichuan-Yunnan region. Regional high-precision 3D community velocity models are fundamental for these studies. In this paper, by assembling seismic observations at permanent seismic stations and several temporary dense seismic arrays in this region, we obtained about 7.06 million body wave travel time data (including absolute and differential travel times) using a newly developed artificial intelligence body wave arrival time picking method and about 100,000 Rayleigh wave phase velocity dispersion data in the period range of 5–50 s from ambient noise cross-correlation technique. Based on this abundant dataset, we obtained the three-dimensional high resolution Vp and Vs model in the crust and uppermost mantle of southwest (SW) China by adopting the joint body and surface wave travel time tomography method considering the topography effect starting from the first version of community velocity model in SW China (SWChinaCVM-1.0). Compared to SWChinaCVM-1.0, this newly determined velocity model has higher resolution and better data fitness. It is accepted by the China Seismic Experimental Site as the second version of the community velocity model in SW China (SWChinaCVM-2.0). The new model shows strong lateral heterogeneities in the shallow crust. Two disconnected low velocity zones are observed in the middle to lower crust, which is located in the Songpan-Ganzi block and the northern Chuandian block to the west of the Longmenshan-Lijiang-Xiaojinhe fault, and beneath the Xiaojiang fault zone, respectively. The inner zone of the Emeishan large igneous province (ELIP) exhibits a high velocity anomaly, which separates the two aforementioned low velocity anomalies. Low velocity anomaly is also shown beneath the Tengchong volcano. The velocity structures in the vicinity of the 2008 Ms8.0 Wenchuan earthquake, the 2013 Ms7.0 Lushan earthquake and the 2017 Ms7.0 Jiuzhaigou earthquake mainly show high Vp and Vs anomalies and the mainshocks are basically located at the transition zone between the high and low velocity anomalies. Along with the segmentation characteristics of seismic activity, we suggest that areas with significant changes in velocity structures, especially in active fault zones, might have a greater potential to generate moderate to strong earthquakes. [ABSTRACT FROM AUTHOR]

On December 29, 2020, nine months after the March Mw 5.4 Zagreb earthquake and amidst the COVID-19 lockdown, a devastating Mw 6.4 earthquake struck near the town of Petrinja, about 50 km SE from the country's capital Zagreb. It was preceded by the Mw 4.9 foreshock from the day before. The main shock claimed 7 fatalities and caused widespread damage. Historical centers of nearby cities with invaluable heritage buildings were significantly affected as were the many residential buildings, built mainly of unreinforced masonry. Damage was observed as far as 60 km from the epicenter. This paper summarizes the seismological aspects of the Mw 6.4 Petrinja earthquake, the emergency response and the main impacts to people and buildings. The description and findings are based on the field observations and a series of post-earthquake activities led by the team of the Faculty of Civil Engineering, University of Zagreb. Typical damage to buildings and usability data are presented with examples based on 50,000 inspection results. By far the most affected were the unreinforced masonry buildings, followed by confined masonry, whereas reinforced concrete buildings were the least affected. The total direct and indirect losses are estimated to 4.8 billion EUR. The provided information represents a useful basis and impetus for improving emergency action and long-term disaster reduction plans in other regions with similar building exposure and seismotectonic settings. [ABSTRACT FROM AUTHOR]

This paper presents analysis of geomorphological indices for predicting the maximum observed earthquake (MOb‒Max) in research region, conducted in three steps: (i) determination of the magnitude of completeness (Mc) of the study area; (ii) assessment of the sensitivity of the geomorphological indicators (10 indices) to earthquake magnitude prediction; (iii) determination of the MOb–Max value. With a multilayer perceptron (MLP) neural network model with one hidden layer (10-14-1) and three methods of data sensitivity assessment for neural networks (Garson's algorithm, Olden's algorithm, Partial Derivatives method) combined with the simple ranking method, we evaluated the importance of 10 geomorphological indices correlated with earthquake magnitude. We find that group-1 is drainage density index (L) and Slope index (S) (average rank 28.5). Group-2 is the mountain front sinuosity index (Smf), drainage basin shape index (Bs) (average rank 18). The most important group-3 is asymmetry factor index (AF), focal statistics index (ΔGH) and hypsometric integral index (HI) (average rank 13.4). The last group-4 with the lowest earthquake magnitude correlation value includes stream length‒gradient index (SL), valley floor width to height ratio (Vf), fractal dimension (FD) (average rank 10.7). Using an MLP neural network with one hidden layer (8-18-1) and eight input geomorphological indices (L, S, Smf, Bs, AF, ΔGH, HI, SL), the earthquake prediction within the Cao Bang and neighboring provinces becomes MOb‒Max = 6.0 and includes the following seven sources: Song (River) Nuoc Den, Song Quay Son, Quang Yen-Song Bang, Cao Bang-Tien Yen, Song Ta Chien, Ha Giang, and Na Hang areas. [ABSTRACT FROM AUTHOR]