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On February 28th, 1969, a large earthquake (M SB w sb = 7.8) strokes the Iberian Peninsula and northern Morocco, producing some casualties and important damage and economic losses. This earthquake is the last large earthquake that has occurred in this region, very near where the catastrophic 1755 Lisbon earthquake took place. The paper by Udías ([11]) is a review of large tsunamigenic earthquakes that occurred at SW of Iberia before the 1755 Lisbon earthquake. [Extracted from the article]

The Bodrum/Kos earthquake that occurred around the island of Kos (Greece) on July 20, 2017, caused serious uneasiness for the people of the region. The earthquake, which occurred 10 km away from Bodrum (36.929° N-27.414° E) at 22:31 UT and at a depth of 7 km, was reported with Mw 6.6. This paper examines the ionospheric anomalies by the means of the total electron content (TEC) map of 61 days. This work utilizes the GNSS-based time-domain TEC map. The TEC (TECU) map is interpolated with Bodrum, Turkey, locations at 35.000° N-37.500° N and 25.000° E-30.000° E. This problem presents a frequency-domain TEC map by exhibiting its amplitudes with Fourier transformation spectral analysis. Earthquakes, solar activities, and geomagnetic storms that can potentially reason anomalies are studied in this essay. The F10.7 (sfu) governs the solar activity effect. OMNI web space weather condition tools direct geomagnetic storms discussion. Statistical approach determines the TEC map boundaries. The TEC map out of the boundaries is marked as an anomaly. The paper detects 11-day TEC map anomalies (7 of these days are before the earthquake). As any space weather condition effect could not be detected, the anomalies on June 22 and 23 and July 1, 2, and 4 possibly are the precursors of the Bodrum/Kos event. The anomalies on July 8 and 15 are probably associated with the earthquake and geomagnetic storms. The source of the anomaly on days July 21 and August 3, 5, and 20 may be the aftershocks of the earthquake and geomagnetic storms. [ABSTRACT FROM AUTHOR]

Timber structures are important components of the architectural and cultural heritage. To enrich literature on reconnaissance and heritage preservation, this paper provides a comprehensive damage survey and assessment of the Shuanghe Confucian temple after the 2019 Changning earthquake Series. Confucian temple is a temple for the veneration of Confucius and the sages and philosophers of Confucianism in Chinese folk religion and other East Asian religions. The Shuanghe Confucian temple, which sits in southwestern China, was first built at about 1241, but have been gradually deteriorating and refurbished for 600 years. It has the supreme structural grade in ancient Chinese architecture and delicate local characteristics. On June 17th, 2019, an Ms 6.0 earthquake stroke Changning County, and another four earthquakes (aftershocks) with magnitude larger than Ms 5.0 took place in the next 20 days. The Shuanghe Confucian temple experienced very distinctive damage during the earthquake series. The paper first present sufficient ground motion information. Characteristics of the all the major structural components are also introduced along with their mechanical functions. Next, the damage of all the typical timber structural components, like roof overhangs drop, column rupture, column bottom lateral residual displacement, and non-structural components failure are carefully documented and assessed. The paper reveals two important aspects that some major damages of the Shuanghe Confucian temple occurred in aftershocks, and that the columns bottom lateral residual displacement was caused by eternal impact induced by adjacent wall collapse, instead of structural inner forces. Thus, this paper helps better understand the seismic performance of traditional timber structures and identify potential weaknesses which might have adverse influences on timber structures. Lessons learnt from the Shuanghe Confucian temple can be used in future to better protect other historical timber structures from earthquakes. [ABSTRACT FROM AUTHOR]

Abstract—This paper analyzes the use of the automated aftershock hazards assessment system (AFCAST) through the example of a series of aftershocks of the Mw 7.8 earthquake in Turkey of February 6, 2023 (the Pazarcik earthquake). The paper presents automated estimates of the aftershock activity area, the magnitude of the strongest aftershock, and the duration of the hazardous period, yielded using data on the main shock and on the first aftershocks. [ABSTRACT FROM AUTHOR]

In this paper, using natural earthquake P-wave arrival time data recorded by the seismic network in the surrounding area of Madoi, the three-dimensional fine P-wave crustal velocity structure at depths above 60 km in the epicenter of the Madoi Ms7.4 earthquake was inverted using the double-difference seismic tomography method. On the basis of the relocation of the source of the aftershock sequence, we summarized the strip-shaped distribution characteristics along the strike of the Jiangcuo fault, revealing the significant heterogeneity of the crustal velocity structure in the source area. Research has found that most of the Madoi Ms7.4 aftershocks were located in the weak area of the high-speed anomaly in the upper crust. The focal depth changed with the velocity structure, showing obvious fluctuation and segmentation characteristics. There was a good correspondence between the spatial distribution and the velocity structure. The high-velocity bodies of the upper crust in the hypocenter area provided a medium environment for earthquake rupture, the low-velocity bodies of the middle crust formed the deep material, and the migration channel and the undulating shape of the high-speed body in the lower crust corroborated the strong pushing action in the region. The results confirmed that under the continuous promotion of tectonic stress in the Madoi area, the high-speed body of the Jiangcuo fault blocked the migration of weak materials in the middle crust. When the stress accumulation exceeded the limit, the Madoi Ms7.4 earthquake occurred. Meanwhile, the nonuniform velocity structure near the fault plane determined the location of the main shock and the spatiotemporal distribution of the aftershock sequence. [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]

Numerous studies have been reported in literature for plate anchors in saturated or dry clays. However, in practical scenario the soil overlying the anchor plate in most of the cases is in unsaturated state, and even then, no study seems to be available for anchors in unsaturated soil. The uplift capacity depends on the resistance of soil overlying the anchor plate, which is in turn affected by the shear strength of soil and varies with variation in the matric suction owing to changes in surface flux conditions and position of the water table. Hence, it has been planned to study the uplift capacity of horizontal strip plate anchors buried in unsaturated clay in this paper. The stress-based limit analysis with the help of finite elements and second-order cone programming has been used for performing the analysis considering the variation of matric suction with depth above the water table under various surface flow conditions (evaporation, no flow and infiltration). Unified effective stress approach-based modified Mohr–Coulomb yield criterion was used to include the influence of stress due to matric suction to the ultimate failure state. The uplift capacity was expressed in terms of a non-dimensional uplift capacity factor, which has been found to be dependent on the embedment depth-to-width ratio of anchor, shear strength parameters of soil, water table position, various flow conditions and their flow rate. The effect of other parameters like air-entry pressure and pore-size distribution parameters, degree of saturation, specific gravity of soil solids, and soil–anchor interface roughness has also been examined and was found to be insignificant. The solutions were presented for an immediate breakaway condition, i.e., considering that the contact between anchor and underlying soil mass is separated at ultimate failure. [ABSTRACT FROM AUTHOR]

The characteristics of aftershocks can be quite different from those of mainshocks. However, most of the works in the past have generally focused on the aftershocks of strong earthquakes, while some moderate earthquakes can cause aftershocks with magnitudes close to the mainshocks. This paper focuses on the aftershocks characteristics of the 2012 Varzaghan–Ahar Doublet event (Mw = 6.4, 6.2), northwest of Iran. Numerous aftershocks with magnitudes 3.7–5.5 recorded by the local seismic stations provide useful data to study the spectral characteristics at various periods. The predictive capability of the 2008 Next Generation Attenuation along with two regional models has been examined by several aftershock records obtained during these events. This paper is the first attempt made to compare the predictive capability of modern models based on significant aftershock data obtained for these two moderate events. Results confirmed that the ground motion models which have been derived based on larger-magnitude events should not directly be extrapolated to predict aftershock ground motions with magnitude smaller than 5.5, especially when we use relationships that developed without considering aftershock data. The residual analysis showed that the model of Abrahamson and Silva (Earthq Spectra, 24(1): 67–97, 2008) performed the best overall predictions in this study. However, this model performs poorly in the short period of 0.2 s at distances greater than 50 km which underestimates the spectral values for this case. [ABSTRACT FROM AUTHOR]

In this paper, an automatic aftershock forecasting system for China is presented. Based on a parameter-free historical analogy method, this system can produce short-term aftershock forecast, including seismic sequence types and the magnitude of the largest aftershock, within a few minutes after a major earthquake and can further provide scientists and government agencies with a set of background information for consultation purposes. First, the system construction concept and operation framework are described, and an evaluation of the forecast performance of the system is then conducted considering earthquakes from 2019 to 2021 in mainland China. The results indicate that the sequence type classification precision reaches 83.5%, and the magnitude of more than 90% of the aftershocks is smaller than that of upper range forecast. This system is fast and easy to control, and all the reports and maps can be produced approximately 5 min after earthquake occurrence. Practical use verifies that the application of this system has greatly improved the efficiency of post-earthquake consultation in mainland China. [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]

This paper describes the methods and results of the strong ground motion simulations for three earthquakes from the 2016 Kumamoto earthquake sequence using corrected empirical Green's functions. The target earthquakes were an aftershock (Mw 5.5), the largest foreshock of the sequence (Mw 6.1), and the mainshock (Mw 7.1). The corrected empirical Green's function method was used in the simulations. This simulation method combines simple source and path factors with empirical site amplification and phase factors to generate realistic site-specific strong motions. Simulations were originally conducted to participate in blind prediction exercises in ESG6. Although the simulations performed in this study were based on the models submitted to the blind prediction committee, several modifications were made after the blind prediction exercise. First, the observed records at the target site of the blind prediction called KUMA were used to compare observed and synthetic strong ground motions. In addition, a regional spectral inversion was conducted to obtain a more appropriate Q-value and site amplification factor. Synthetic strong motions were found to explain the observed strong ground motions at KUMA and other stations. Comparisons with predictions by other methods and the sensitivity to the rupture scenario were also discussed. These results provide useful information for applying the corrected Green's function method to strong ground motion simulations. [ABSTRACT FROM AUTHOR]

Seismic catalogs are vital to understanding and analyzing the progress of active fault systems. The background seismicity rate in a seismic catalog, strongly associated with stressing rate, is the critical parameter in seismic hazard analysis. Estimating background seismicity is a complex task due to the high correlation with aftershock sequences which may dominate the background seismicity rate. In this paper, identification of the significant earthquake aftershocks and independent background events is performed using a two-stage clustering approach. It works in two phases: Self-Organized Map and Density-based Temporal Clustering. The event's location and depth information in the earthquake catalog is used to identify the major hot spots (SOM prototypes) in the region (Spatial domain). Later, density-based temporal clustering is applied to decipher the neighborhood events of each SOM prototype. The proposed two-level clustering approach performs effective spatio-temporal analysis and identifies the aftershock clusters and background. The experimental study is carried out on the prominent earthquake catalogs of Taiwan, Afghanistan, California, the Himalayas, Indonesia, Chile, and Japan. The statistical parameters: Coefficient of Variation (time-domain) and m-Morisita index (spatial domain) justify and validate the accuracy of the presented approach. The proposed model is compared with benchmark de-clustering algorithms for mainshock and background detection. [ABSTRACT FROM AUTHOR]

In statistical seismology, the Epidemic Type Aftershocks Sequence (ETAS) model is a branching process used world-wide to forecast earthquake intensity rates and reproduce many statistical features observed in seismicity catalogs. In this paper, we describe a fractional differential equation that governs the earthquake intensity rate of the pure temporal ETAS model by using the Caputo fractional derivative and we solve it analytically. We highlight that the tools and special functions of fractional calculus simplify the classical methods employed to obtain the intensity rate and let us describe the change of solution decay for large times. We also apply and discuss the theoretical results to the Japanese catalog in the period 1965-2003. [ABSTRACT FROM AUTHOR]

The 25th April 2015 Nepal earthquake was the first major event in the Himalayan orogeny to provide a relatively well-recorded dataset. This paper presents a comprehensive analysis of the mainshock and its five major aftershocks through 21 well-established ground motion parameters. The analysis is presented for near-field stations of the Kathmandu basin and far-field stations of the Indo-Ganga Plains, including the site response behavior with varying sediment depths. Moreover, Hilbert–Huang Transform is used to study site amplifications associated with sediment depth and soil class, especially at long periods. In addition, a new ground motion model (GMM) is derived for all 21 parameters using moment magnitude, source-to-site distance, site class and sediment depth as predictor variables. Further, to ensure that the developed GMM is not biased, an inter-event and intra-event residual analysis is performed. Furthermore, the GMM is compared with other well-established prediction models applicable to the study region. The efficacy of the current model is further addressed by the evaluation of ranking indices. [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]

The semiempirical approach based on envelope summation method given by Midorikawa (Tectonophysics 218:287-295, ) has been modified in this paper for modeling of strong motion generation areas (SMGAs). Horizontal components of strong ground motion have been simulated using modifications in the semiempirical approach given by Joshi et al. (Nat Hazard 71:587-609, ). Various modifications in the technique account for finite rupture source, layering of earth, componentwise division of energy and frequency-dependent radiation pattern. In this paper, SMGAs of the Uttarkashi earthquake have been modeled. Two different isolated wave packets in the recorded accelerogram have been identified from recorded ground motion, which accounts for two different SMGAs in the entire rupture plane. The approximate locations of SMGAs within the rupture plane were estimated using spatio-temporal variation of 77 aftershocks. Source parameters of each SMGA were calculated from theoretical and observed source displacement spectra computed from two different wave packets in the record. The final model of rupture plane responsible for the Uttarkashi earthquake consists of two SMGAs, and the same has been used to simulate horizontal components of acceleration records at different station using modified semiempirical technique. Comparison of the observed and simulated acceleration records in terms of root mean square error confirms the suitability of the final source model for the Uttarkashi earthquake. [ABSTRACT FROM AUTHOR]

The outcomes of this study are necessary to assess seismic hazard in Kuwait. The noticeable increase in urban development and construction of tall structures and skyscrapers highlights the importance of seismic risk analysis and the creation of a unified seismic code for Kuwait. This paper can be considered as an initial step through the assessment and deaggregation of seismic hazards in Kuwait. To achieve this purpose, a complete seismic catalog for Kuwait and the active Zagros Seismic Belt has been created containing all the available historical and instrumental earthquakes, unified in magnitude and foreshocks and aftershocks removed. Alternative seismotectonic models were built basing on structural geological situation, seismicity and focal mechanisms. The recurrence parameters along with the maximum expected earthquake from all seismic sources were basically estimated. Appropriate ground motion prediction relation within a logic tree formulation was fundamentally used in creating seismic hazard maps. A state-of-the-art probabilistic approach is used in this study to produce hazard maps at 75, 475, 975, and 2475 years return periods (equivalent to 50%, 10%, 5%, and 2%, respectively, probability of exceedance in 50 years) at the PGA, 0.1, 1 and 4 s spectral periods. The hazard maps were computed using a spacing grid of 0.1° × 0.1° across the Kuwait area. Uniform hazard spectra and deaggregation of seismic hazard have been established for the governorates of Kuwait. Additionally, a sensitivity analysis was performed for theses governorates to reduce uncertainties in the seismotectonic source models, predictive ground motion equation and maximum expected earthquake magnitude. These results with vulnerability index are essential components for seismic risk analysis in Kuwait. [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]

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]

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]

The observation of electromechanical coupling might be used as an important tool to detect pre-seismic changes associated with the preparation of earthquakes. This paper attempts to study the electromechanical coupling process before the large earthquakes by using the load/unload response ratio (LURR) approach in which the geo-electric data and Benioff strain of small earthquakes were adopted as the data input. The variation of Coulomb failure stress induced by earth tides on the fault surface of the mainshock is applied to differentiate the loading and unloading stages. Using this technique, we test the geo-electric data recorded at the Hotan observatory near the epicenter of 2020 Yutian Ms 6.4 earthquake. Results show that the LURR time sequence fluctuated around 1.0 for many years and reached significant high peaks at the beginning of 2020. More importantly, this evolution correlates well with the LURR time series calculated by using the Benioff strain of small earthquakes within the circular region of 300 km radius centered at the epicenter. The underlying physics of the changes should be caused by the fluid infiltration derived from pre-seismic rock dilatancy. The corresponding volume variations in the crust could be found in the geophysical observation time series in the same neighborhoods. [ABSTRACT FROM AUTHOR]

One hundred years ago, Fusakichi Omori died. Our paper is dedicated to his memory. Omori made an outstanding contribution to the physics of earthquakes. In 1894 he formulated the law of aftershock evolution. Omori’s Law states that after the main shock of an earthquake, the frequency of aftershocks decreases hyperbolically with time. In this paper, we briefly describe one of the directions of modern aftershock research. We present Omori’s law in the form of a differential equation describing the evolution of aftershocks. The evolution equation allows us to solve the inverse problem of the earthquake source “cooling down” after the main shock. The solution of the inverse problem allowed us to reveal the existence of the so-called Omori epoch. It is established that at the end of the Omori epoch something similar to a bifurcation of the source state occurs. A logistic equation supposedly describing the bifurcation phenomenon is proposed. [ABSTRACT FROM AUTHOR]

This document is a correction notice for an article titled "Stable estimation of the Gutenberg-Richter b-values by the b-positive method: a case study of aftershock zones for magnitude-7 class earthquakes." The authors of the original article reported that three in-text citations were mistakenly written as "accepted" instead of the correct year. The citations should be changed to "Mitsui et al. 2024." The original article has been updated to reflect this correction. The publisher, Springer Nature, remains neutral regarding jurisdictional claims and institutional affiliations. The correction notice was reported by Yuta Mitsui. [Extracted from the article]

The January 24, 2020 Sivrice-Elazığ (Mw = 6.8) earthquake occurred on the East Anatolian Fault zone. Main shock of this earthquake was occurred 20:55 at local time. The Peak Ground Acceleration was equal to 0.3 g at the epicenter (Sivrice district) of the earthquake. Even though the main shock was moderate, its effects on the structures were rather serious. The main shock caused significant damage and resulted in 41 casualties. 1540 buildings were damaged moderately, while 8519 buildings were damaged heavily and collapsed. This main shock effected four cities surrounded the epicenter due to its shallow earthquakes. The purpose of this paper is to summarize past and present seismic characteristics of the earthquake region. In addition, the aim of this paper is to summarize the seismotectonic of the region, the general characteristics of the earthquake and more specifically to report on the structural damage, and structural damage caused by the earthquake, observed during the site investigation. The damages were classified for reinforced concrete structures, masonry dwellings and non-residential structures. All distinguished earthquake induced failures and damages were discussed. Moreover, lessons learned were presented in this study. [ABSTRACT FROM AUTHOR]

Since post-mainshock events following a major earthquake are likely to occur, it is imperative to have an understanding of the functionality status of mainshock-damaged bridges to make more informed decisions. This paper examines the post-earthquake operability of a typical highway bridge class in reference to the time-varying nature of aftershock hazard by using the residual collapse capacity of the mainshock-damaged bridge. A procedure for estimating the probabilistic system-wide residual capacities to withstand aftershocks resulting from the residual capacities of vulnerable major bridge components across damage states is discussed. Based on varying earthquake scenarios, the probability of transiting to all post-mainshock and post-aftershock damage states are calculated for intact and mainshock-damaged bridges, respectively. It is observed that as the level of mainshock-sustained damage increases, the probability of experiencing more damage due to aftershocks decreases. Using the probability distribution of the intact collapse capacity or residual collapse capacity across post-mainshock damage states in combination with the mainshock and aftershock hazard curves, respectively, the annual probability of collapse for the location of interest is obtained. Having determined the intact and residual collapse capacities, as well as the site-specific mainshock and aftershock hazards, the tagging condition of the damaged bridge in the aftermath of an earthquake due to the possible future aftershocks, is evaluated by computing the equivalent constant collapse rate. The required time for imposing traffic restrictions on the mainshock-damaged bridge due to the life-safety threats in the aftershock environment is specified for various earthquake scenarios. [ABSTRACT FROM AUTHOR]

Many moderate to large historical and instrumental events have been documented in the Mitidja basin, affecting in particular the southern edge of the active Quaternary Mitidja basin, which is composed of nearly NE–SW-trending fault system. The earthquake catalogue reports that the Hammam Melouane region has experienced several moderate seismic events such as those of 8 February 1937 (I0 = V), 20 July 1975 (I0 = V–VI), 29 September 1981 (I0 = V) and 17 December 1986 (I0 = V). Recently, between 2013 and 2016, this area experienced three moderate earthquakes with a series of aftershocks. In this paper, we present an analysis of the seismic sequences that occurred in the Hammam Melouane Geothermal Spring area on 17 July 2013 (ML 4.9), 23 December 2014 (ML 5.3) and 10 February 2016 (Mw 4.8), about 3–7 km apart, at hypocentral depths of 11.5 km, 19.0 km and 18.0 km, respectively, with centroid depth of 5 km for the first main shock. Ninety-seven events with local magnitude ranging between ML 0.9 and ML 5.3 were recorded and analyzed. The series of aftershocks display two clusters, trending N–S for the 2013 event and NE–SW for the 2014 event, located at shallow depths of 1.5–14 km and 18–28 km, respectively. The event distribution shows variability in faulting, combining strike-slip and thrust focal mechanisms of the main events, leading us to hypothesize a simultaneous interaction between two geological active structures represented by the ~ N–S- to NE–SW-trending faults belonging to the southern Mitidja fault system. On one hand, the computed ΔCFF indeed supports and strengthens the fault interaction model between the three events. On the other hand, the analysis of the post-seismic stress distribution caused by fluid circulation reveals that the 2013 and 2014 events seem to have caused a poroelastic stress relaxation and thus influenced the occurrence of the 2016 main shock. [ABSTRACT FROM AUTHOR]

In the aftermath of a seismic event, decision-makers have to decide quickly among alternative management actions with limited knowledge on the actual health condition of buildings. Each choice entails different direct and indirect consequences. For example, if a building sustains low damage in the mainshock but people are not evacuated, casualties may occur if aftershocks lead the structure to fail. On the other hand, the evacuation of a structurally sound building could lead to unnecessary financial losses due to business and occupancy interruption. A monitoring system can provide information about the condition of the building after an earthquake that can support the choice between several competing alternatives, targeting the minimization of consequences. This paper proposes a framework for quantifying the benefit of installing a permanent seismic structural health monitoring (S2HM) system to support building evacuation operations after a seismic event. Decision-makers can use this procedure to preventively evaluate the benefit of an SHM system and decide about the worthiness of its installation. [ABSTRACT FROM AUTHOR]

In this paper we consider four moderate earthquakes that occurred on November 9, 2011; September 5, 2015; March 16, 2018; and October 10, 2019, in the southern basin of Baikal Lake near the Goloustnaya River delta. Seismotectonically, the earthquake sources are confined to the southwestern part of the Olkhon graben. The earthquake focal mechanisms allow us to suggest the activity of local submeridional faults, feathering the structures of the general northeast strike. For two seismic events, the following parameters were determined: scalar seismic moment M0 = 4.0 × 1015 N m, moment magnitude Mw = 4.4, and source depth h = 12 km for the September 5, 2015 earthquake and M0 = 2.2 × 1015 N m, Mw = 4.2, and h = 7 km for the March 16, 2018 earthquake. None of the seismic events was followed by noticeable aftershock activity. In 2011–2019, these earthquakes caused a noticeable macroseismic effect within the Irkutsk agglomeration, as well as a rather wide public response. Macroseismic data were collected mainly using an online survey system; the number of responses received within the first day after an earthquake varies from 127 to 341. The maximum intensity, IV–V, was observed for the November 9, 2011 earthquake in the settlement of Bolshoye Goloustnoye. The results can be used for assessing the seismic hazard in the Southern Baikal region. [ABSTRACT FROM AUTHOR]

In this paper, we kinematically analyze the movements of plates and blocks of the region of southeastern Turkey, where strong earthquakes occurred on February 6, 2023, based on a homogeneous database of displacement velocities of GNSS permanent monitoring stations. Along the East Anatolian fault zone from 2008 to 2018, the Arabian Plate was established to shift relative to the Anatolian Plate, which corresponds to a left shift (without a normal component) at a rate from 1 cm/yr in the eastern part to 0.8 cm/yr in the western part. Along the Chardak fault, displacements corresponding to the left shift occurred at a rate of less than 0.7 cm/year. The revealed kinematics is confirmed by focal mechanisms and cosesismic displacements of the studied earthquakes. The M7.5 earthquake that occurred directly on the Chardak fault is not an aftershock of the M7.8 earthquake, but is a relatively independent event. An analysis of the seismic regime shows that the stresses on the East Anatolian fault after the main M7.8 event are relieved by the first large latitudinal fault zone (the Chardak fault). The results of our study suggest that the counterclockwise rotation of the Anatolian and Arabian plates associated with the opening of the Red Sea Rift is most likely decisive for the general kinematics of the plates in the region. [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]

The paper presents the studies of the Khuvsgul earthquake on January 11, 2021 at 21:32 UTC (January 12, 2021 at 05:32 local time), MW = 6.7, ML = 6.9, and the seismicity structure in the aftershock period for the Altai-Sayan mountain region and the Baikal rift zone, where the epicenter of this earthquake was located. Two faults are seismically activated, diverging from the southern end of the aftershock area at an acute angle: one in the northeast and one in the northwest direction, as well as transverse faults between them. According to the epicenter position and studies of the source area by other authors, the main event corresponds to the northeastern fault, and large aftershocks occurred at the junction of the northwestern fault with transverse faults feathering from the east. The main event was immediately followed by a series of large aftershocks, the strongest of which occurred on March 31, 2021 with ML = 6.2 and on May 3, 2021 with ML = 6.4. Spatial changes in the seismic regime of the aftershock region led to the predominant activity of its southern end. The junction area of the collisional structures of the Altai–Sayan folded zone and the rift structures of the Baikal depressions system is distinguished in seismicity as a block structure with increased seismicity near the block boundaries. First of all, these are the Tuva-Mongolian block and the eastern part of the Sayano-Tuva block. After the Khuvsgul earthquake of 2021, a block structure with the activation of the epicentral zones of the 1991 Busingol earthquake, the 2011–2012 Tuva earthquakes, and other structures seismically active until 2021 has increased seismic activity. It is proved that the 2014 Khuvsgul earthquake occurred under the basin of the same name and is associated with other faults than the 2021 earthquake and is not a direct precursor of the 2021–2022 activation. [ABSTRACT FROM AUTHOR]

In December 2007, an Mw2.2 earthquake occurred in a gabbroic dike at 3.3 km depth in a deep gold mine in South Africa. The fore- and aftershock activity was analyzed in an effort to understand the preparation and generation processes of earthquakes; these findings have already been published. The present paper focuses on the stress state in the source region of the mainshock. A 90-m-long borehole across the mainshock fault was drilled ~ 1.5 years after the mainshock and logged by an optical televiewer. The fault can be identified by severe damage to the borehole wall at the point where the borehole intersected the aftershock cluster. Except for a 10-m section in the hanging wall of the fault, borehole cores were fully recovered. Borehole breakout (BO) and core disking (CD) were found to occur. Two stress measurement techniques [Deformation Rate Analysis (DRA) and Diametrical Core Deformation Analysis (DCDA)] were applied to the borehole cores. By combining their results with occurrence criteria for BO and CD, the principal stress state in the source region of the mainshock was determined. The principal directions in the hanging wall of the fault were nearly identical to the virgin stress state, while it was significantly disturbed in the footwall. The vertical stresses were 106 MPa and 40 MPa in the hanging wall and footwall, respectively. The significant difference in the vertical stress between the two sides of the fault can be explained by the stress redistribution associated with a nonuniform slip on a nonplanar fault. [ABSTRACT FROM AUTHOR]

This paper deals with the Omori and Bath laws describing the properties of aftershocks of strong earthquakes. We reformulated Omori's law by presenting it as a differential equation for the evolution of aftershocks. This allowed us to introduce the idea of a deactivation coefficient for the earthquake source "cooling down" after the main shock. In the course of this work, we found a strong dependence of the deactivation coefficient on the magnitude of the main shock. In the case of Bath's law, we determined the value of the difference between the main shock magnitude and the magnitude of the strongest aftershock at the initial stage of aftershock evolution. In addition, we modified the formulation of the problem by introducing the concept of so-called "mirror" foreshocks and established a law for them similar to Bath's law. [ABSTRACT FROM AUTHOR]

Aftershocks have the potential to further aggravate the damage of masonry structures caused by mainshock. To quantitatively analyze the effect of aftershocks, this paper investigates the seismic response of unreinforced masonry structures subjected to mainshock-aftershock (M-A) sequences. Firstly, an analytical method for estimating the maximum storey drift of masonry structures subjected to M-A sequences is proposed, which is based on the non-iterative equivalent linearization method and the soft-storey failure mechanism of multi-storey masonry structures. Then, a finite element method is employed to verify the effectiveness of the proposed method. Finally, a parametric analysis is performed to evaluate the effects of aftershock intensity, anti-seismic wall area ratio, site classes, number of storeys, and mortar strength on the seismic responses of masonry structures subjected to M-A sequences, respectively. The results indicate that an excellent agreement for the maximum storey drift (θmax) between analytical and numerical results. The effect of aftershocks on masonry structures in plastic phase is more distinct than that in elastic phase. Furthermore, the effect of aftershocks on the θmax of masonry structures can be ignored when the relative intensity of aftershock is less than 0.5, and the θmax can increase by approximately 19.0% when the relative intensity of aftershock is equal to 1.0. Additionally, for the masonry structures subjected to M-A sequences, the effects of site classes on the θmax cannot be ignored, the θmax can decrease with increasing anti-seismic wall area ratio and mortar strength, and increases with increasing number of storeys. [ABSTRACT FROM AUTHOR]

The 2013 Lushan Ms 7.0 earthquake occurred on the Longmenshan thrust tectonic zone, a typical blind reverse-fault type earthquake that caused the death of nearly 200 people. The investigation of the fault geometry and fault slip distribution of this earthquake is important for understanding the seismogenic tectonic type and seismic activity mechanism of the Longmenshan Fault Zone. In this paper, for the fault geometry of the Ms 7.0 earthquake in Lushan, the geometric parameters of the planar fault are inverted based on the rectangular dislocation model using GPS coseismic displacement data, and on this basis, a curved fault steeply-dipping on top and gently-dipping at depth is constructed by combining the aftershock distribution. The GPS and leveling data are used to invert the slip distribution of the curved fault for the Lushan Ms 7.0 earthquake. The results show that the fault is dominated by reverse slip with a small amount of sinistral rotation, and there is a peak slip zone with a maximum slip of 0.98 m, which corresponds to a depth of ~ 13.50 km, and the energy released is 1.05 × 1019 N/m with a moment magnitude of Mw 6.63. Compared with the planar rectangular dislocation model, the curved fault model constructed by using triangular dislocation elements can not only better approximate the fault slip, but also better explain the observed surface displacement, and the root mean square error of the GPS and leveling data fitting is reduced by 1.3 mm and 1.9 mm, respectively. Both the maximum slip and moment magnitude of the fault based on the inversion of the curved structure are slightly larger than the results based on the planar structure. [ABSTRACT FROM AUTHOR]

Earthquake depth frequency distribution is often used as a constraining factor in assessing lithospheric strength. The accuracy of hypocenter locations is therefore a key factor in these types of analyses. This paper presents a summary of earthquake depth distributions in the Baikal rift system reported in various previous studies. Datasets on both background seismicity and aftershock sequences were analyzed by taking into account hypocenter depth uncertainties. The results show that the most seismically active part of the Earth's crust is in a depth range of 10–25 km. The lower cutoff depth varies for different datasets from 20 to 40 km. The latter value corresponds to the Kichera sequence and coincides with the Moho depth, but other datasets show that the lower 8–18 km of the crust is aseismic. The South Baikal basin is distinguished by the shallower cutoff depth (20–24 km) compared to the datasets outside of it. The peak depths of the earthquake depth frequency distributions vary from 8 to 23 km. Given the depth uncertainties, only the Kumora sequence appears to have double peaks at 9–10 km and 16–17 km. Variations in the lower limit of earthquake distribution and depth of the main peak may imply a spatial change in the depth of the brittle–ductile transition and consequently in the thermomechanical properties of the crust. [ABSTRACT FROM AUTHOR]

Making a decision on the post-earthquake functionality of structures has always been one of the most challenging issues in earthquake engineering. There is an increasing trend toward resilient infrastructures that their post-earthquake functionality is planned so that the life and economic losses after the occurrence of earthquakes would be mitigated. Bridges, as the main elements of the transportation network, have received less attention in this regard. Deciding on the post-earthquake functionality of bridges is mostly subjective and based on the judgment of the inspectors. This paper aims to present an analytical-empirical decision-making framework for expediting the decision on the post-earthquake functionality of bridges that employs the damage data from inspections. The proposed framework is a two-phased probabilistic procedure that adopts the damage state and residual displacement of the bridge after the mainshock, and the possible aftershock characteristics as well. The link between the functionality of the bridge, allowed traffic, and the state of the damaged bridge is made with consideration of the uncertainties. The proposed framework is implemented on a sample bridge, and the decision procedure is illustrated. [ABSTRACT FROM AUTHOR]

The design earthquake is usually specified as a single event in most of modern seismic codes. However, one earthquake is often followed by a series of aftershocks called seismic sequence. Such cases are quite common, especially in near-fault regions, which could cause additional accumulated damage to structures. In this paper, a new methodology for evaluating the effect of near-fault seismic sequences on the accumulated damage of reinforced concrete (RC) frame structure is proposed, in which different initial damage levels (i.e., postmainshock global damage index) of structure after the mainshock are considered. Meanwhile, a quantitative description of the damage demands and the relative intensity index between mainshock and aftershock are provided. For this purpose, the nonlinear dynamic response of an eight-story RC frame structure subjected to single earthquake and seismic sequence is compared in terms of structural performance indices (collapse capacity, story damage demands, postmainshock damage level and normalized hysteretic energy) and relative intensity index. The results indicated that seismic sequences lead to reduced collapse capacity of postmainshock-damaged structures. Moreover, the near-fault pulse-like aftershock records would induce larger structural story damage demands than ordinary (i.e., non-pulse-like) aftershock records. Furthermore, the relative intensity index proposed in this paper has significant effects on the structural story damage demands, incremental dynamic analysis curves of aftershock and normalized hysteretic energy. [ABSTRACT FROM AUTHOR]

In this study, based on the body wave arrival data of 5506 earthquakes recorded by 32 fixed stations and 94 temporary stations in Yangbi and surrounding areas, the source parameters of Yangbi Ms6.4 earthquake sequence and three-dimensional (3-D) fine Vp, Vs, and Vp/Vs were inverted by using the consistency-constrained double-difference tomography method. The results showed that the focal depth after relocation was mostly in the range of 3–10 km, evidently nearly horizontally distributed, and concentrated in the weak area of the high-velocity body or at the side of the high-low-velocity body transition zone toward the high-velocity body, showing a good corresponding relationship with the velocity structure. The velocity structure in the Yangbi area has remarkably uneven characteristics. The seismic activity area is dominated by high-velocity bodies prone to brittle fracture near the surface. As the depth increases, low-velocity anomalies appear. A significant difference was observed in the wave velocity ratio between the upper and lower sides of the seismically dense strip. Based on the focal mechanism of the Yangbi Ms6.4 earthquake and the fine 3-D velocity structure, this article concludes that the Yangbi Ms6.4 earthquake was caused by a strong regional tectonic stress concentrated in the relatively weak area by hard high-velocity bodies on the northwest sides. The Ms5.6 foreshock broke the inherent balance of regional stress and promoted the occurrence of the Yangbi Ms6.4 mainshock. Afterward, the stress was adjusted to a new equilibrium state through a large number of aftershocks, forming a foreshock-mainshock-aftershock type of seismic activity model. Based on the activity law of the Yangbi Ms6.4 earthquake sequence and characteristics of the 3D velocity structure distribution, this paper speculates that the seismogenic structure of the Yangbi earthquake was possibly a northwest strike-slip buried fault with a depth of 3–10 km on the southwest side of the Weixi-Qiaohou fault. [ABSTRACT FROM AUTHOR]

The paper presents a general outline of the phenomenological theory of aftershocks, i.e., subsequent shocks that occur in the source volume after the main shock. It is proposed to describe the evolution of aftershocks in time by the logistic Ferhulst equation. Apparently, the well-known Kolmogorov–Petrovsky–Piskunov (KPP) equation can serve as a basis for further development of the theory. The KPP equation has solutions that simulate the effect of slow aftershock propagation. The logistic equation describing the evolution of aftershocks averaged over the epicenter zone follows from it. The proposed approach may be useful in searching for models of foreshocks, main shock, and earthquake swarms. [ABSTRACT FROM AUTHOR]

Purpose: This study investigates the seismic performance of vertical irregular steel moment-resisting frames subjected to mainshock–aftershock (MS–AS) seismic sequence. The building structures situated in a seismically active region experience sequence of earthquakes during their lifetime. These seismic sequences have the potential to increase the damage state of the structures. The irregular building structures are present due to availability of space, functional and architectural requirements etc. behave differently as compared to the regular buildings during earthquakes. Methods: In this paper, three steel-moment resisting frames having different configuration i.e. 3, 6, and 9-storey were considered as a reference regular frame. Three vertical irregularities-stiffness, strength and combined stiffness and strength are introduced in three different locations (bottom, mid-height, and topmost storey) along the height of each building frames. These regular and vertically irregular frames are subjected to mainshocks alone and artificial MS–AS seismic sequences that are generated by using the repeated and randomized approach. The nonlinear time-history analysis is performed using computer software SAP 2000 on regular and irregular building frames subjected to mainshocks and MS–AS seismic sequence. Results: The comparison between the seismic performance of vertically irregular and regular frames subjected to mainshocks alone and MS–AS seismic sequences shows that the vertical irregular frames have a significant effect on the distribution of mean interstorey drift demands along the height of building frames. Conclusion: The effect of MS–AS seismic sequence on seismic demands of vertical irregular and regular frames have been increased compared to mainshocks. However, the repeated seismic sequences show smaller structural responses relative to the randomized seismic sequences. [ABSTRACT FROM AUTHOR]

The south segment of the China North-South Seismic Belt is located in the southeast margin of the Qinghai Tibet Plateau. This region is characterized by the frequent seismic activity in Chinese mainland. In this paper, the geomagnetic field model NGDC-720 and the data of terrestrial heat flow are used to investigate the distribution of crustal magnetic anomalies, the depth of Curie surface, and the characteristics of the crustal thermal structure in the south segment of the North-South Seismic Belt. The distribution characteristics of the vertical component ΔZ and the magnetic declination ΔD in the area with earthquakes over a magnitude of 6 and their aftershocks since 1970 are focused on. The results show that the earthquakes are mainly observed in the area of negative magnetic anomaly or the strong and weak transition zone. It especially shows in the ΔD. The Curie surface in the study area varies significantly, ranging from 20.8 to 31 km. The uplift area of the Curie surface is consistent with the high-value area of terrestrial heat flow. The high geothermal area corresponds to the strong earthquake activity area. The focal depth of most strong earthquakes is shallower than the depth of the Curie surface. The strong earthquakes mainly occur in the deep-shallow transition zones of the Curie surface. The results can be used as a reference for strong earthquake prediction in this area. [ABSTRACT FROM AUTHOR]

This paper presents the fragility assessment of non-seismically designed steel moment frames with masonry infills. The assessment considered the effects of multiple earthquakes on the damage accumulation of steel frames, which is an essential part of modern performance-based earthquake engineering. Effects of aftershocks are particularly important when examining damaged buildings and making post-quake decisions, such as tagging and retrofit strategy. The procedure proposed in the present work includes two phase assessment, which is based on incremental dynamic analyses of two refined numerical models of the case-study steel frame, i.e. with and without masonry infills, and utilises mainshock-aftershock sequences of natural earthquake records. The first phase focuses on the undamaged structure subjected to single and multiple earthquakes; the effects of masonry infills on the seismic vulnerability of the steel frame were also considered. In the second phase, aftershock fragility curves were derived to investigate the seismic vulnerability of infilled steel frames with post-mainshock damage caused by mainshocks. Comparative analyses were conducted among the mainshock-damaged structures considering three post-mainshock damage levels, including no damage. The impact of aftershocks was then discussed for each mainshock-damage level in terms of the breakpoint that marks the onset of exceeding post-mainshock damage level, as well as the probability of exceeding of superior damage level due to more significant aftershocks. The evaluation of the efficiency of commonly used intensity measures of aftershocks was also carried out as part of the second phase of assessment. [ABSTRACT FROM AUTHOR]

By comparing damage and loss predictions with those observed for a 22-storey steel building with eccentrically based frames (EBF) that underwent the Canterbury earthquakes, this paper gauges the performance and explores the benefits of applying the PEER performance-based earthquake engineering assessment procedure. The study shows that steel EBF repair costs are significantly affected by the work required to remove and reinstate non-structural elements in order to access the steel structure. It is therefore concluded that the location of non-structural elements relative to structural elements should be considered in the seismic design of new buildings and within loss assessment procedures. Two retrofit and/or rehabilitation options are considered for the building; improving the deformation capacity of drywall partitions, and re-detailing the exterior cladding connections to better accommodate structural deformations. The findings show that, for the specific building, improving the drywall partitions should lead to a reduction in expected annual losses whereas the use of improved detailing for the precast concrete cladding would not. This suggests a general strategy for cost-effective decisions might be to focus on increasing the performance of the most vulnerable components (plasterboard partition walls, in this case). An examination of the potential effects of aftershocks to the selection of cost-effective options adds support to this conclusion. Aftershocks are found to increase the predicted losses by around 10%, emphasizing the need to consider aftershocks when assessing expected annual losses due to earthquakes. [ABSTRACT FROM AUTHOR]

The Kaikoura earthquake on November 14, 2016 is one of the largest and most complex earthquakes in New Zealand since 1947. Despite the fact that it has ruptured about 12 separate faults, triggered 2132 aftershocks within one week of the mainshock and induced considerable stress changes, few studies have been conducted to comprensively investigate the characteristics. The current study examines the horizontal and vertical displacements as well as the stress and gravity changes, aftershock distributions and also find out whether these changes affect the surrounding regions along the complex fault systems. The study covers the entire area affected by the Kaikoura event, which includes the northern part of the South Island and the southern part of the North Island. The dislocation theory was employed to evaluate the coseismic slip model on the multiple faults. The displacement results revealed that the maximum horizontal displacement is about 6 m and the vertical about 2 m, which are reasonably consistent with earlier study findings. Besides, the stress and gravity changes are quite complicated and inhomogeneous as evidenced by our coseismic model, demonstrating the complexity of the Kaikoura earthquake as well. Almost all the aftershocks are distributed in places where the stress and gravity change are found to be significant. In order to investigate the stability of our stress change models, we applied different friction coefficients and receiver fault parameters. The results justify the friction coefficient (μ=0.4) and the receiver fault parameters (230°, 70°, 150°) are suitable to define good stress change estimates. According to the stress change results at 15 km depth, the northern parts of the mainshock region, Hundalee fault, Humps fault and Jordan thrust areas together with the Wellington area are closer to failure and situated in a seismic risk zone. The multidimensional analysis adopted in this paper is helpful for making decisions and applications of stress and gravity change models in assessing seismic hazards. [ABSTRACT FROM AUTHOR]

This paper presents two-stage clustering approach for accurate analysis of earthquake catalogs where aim is to categorize events in terms of aftershock (AF) clusters or independent backgrounds (BGs). In stage I, the Gaussian kernel-based temporal density estimation is used for grouping of events based on their occurrence time. From the graph, local peak (maxima), local minima and their timing information are utilized to group the events into significant time zones. In stage II, on events of each time zone, coordinate and magnitude information is combined together (weighted mechanism) to determine effective local weighted spatial density ( ρ w ). Based on ρ w and event distance (δ ), a decision graph is drawn to find out the spatial cluster centroids for each time zone. Event's assignment to the centroid is carried out based on its nearest neighbor of higher density. Outliers (non-clustered) are also detected in stage II which is considered as independent backgrounds. The experimental analysis is carried out on historical seismicity of California, Himalaya, Japan and Sumatra–Andaman region. The results indicate that obtained AFs and total number of events follow a similar cumulative and λ rate, whereas BGs have linear cumulative and consistent λ rate. It is also observed that AFs and total events have similar ergodic behavior, quantified from the inverse TM metric plot. The competitive performance of the proposed approach is obtained over state-of-the-art declustering methods. [ABSTRACT FROM AUTHOR]

This analysis is an extension of the studies based on the space–time–magnitude domain nearest-neighborhood distances (ƞ) obtained from two successive earthquakes. We included epicentral depth as a parameter, and established a new analytical solution for seismicity clustering in the space–time–depth–magnitude domain. The proposed technique was applied to SW Japan seismic observation data for 2011–2018, and revealed that the temporal, spatial, and epicentral (T, R, E) components of the joint distribution for ƞ were prominently bimodal, indicating the presence of two, statistically distinct, earthquake populations. We used the Lomb–Scargle periodogram (LSP) to generate a power spectrum preceding the Kumamoto earthquake, and detected the periodic component of unequally spaced points for log10ƞ (logarithmic scale of ƞ). The LSP showed a dominant peak corresponding to the time period between foreshocks and aftershocks, due to the highest number of recorded ƞ observations. The technique presented in this paper can be applied globally for any time period and any seismotectonic zone preceding large earthquakes of interest. [ABSTRACT FROM AUTHOR]

Structures in earthquake-prone areas are not subjected to a single seismic event, but also to a seismic sequence consisting of mainshock and several aftershocks. However, the influence of seismic sequence on performance of structures has not been addressed in majority of existing seismic codes. This paper investigates the effect of repeated earthquakes on performance of steel buckling restrained braced frames. For this purpose, 4-story and 10-story prototype buckling restrained braced frames, designed according to Iranian building codes, are exposed to five seismic sequences. Nonlinear time history analyses are conducted and the responses of frames are measured in terms of maximum inter-story and residual drifts. Furthermore, Park–Ang damage indices and global ductility factors are obtained for braced frames under examined mainshocks and mainshock–aftershock sequences. From the results of this research, it is found that the seismic sequence has the potential to increase the inter-story drift, residual drift, damage index and global ductility factor of buckling restrained braced frames. It is also highlighted that the spectral acceleration of mainshock–aftershock sequence, in comparison to that of single event mainshock, considerably affects the performance of buckling restrained braced frame under repeated earthquakes. [ABSTRACT FROM AUTHOR]

The 2015 M 7.8 Gorkha earthquake and its aftershocks caused nearly 9000 deaths and more than 23,000 injuries and triggered thousands of landslides and other mass-wasting effects in the steep, rugged topography of Nepal. In this paper, new slope failures and tension cracks induced by the 2015 Nepal earthquake are documented in steep terrain west of the Tatopani Border Station, which lies along the deeply incised Bhote Koshi River valley, a critical trans-Himalayan transport route between south Asia and Tibet/China. The affected area west of the Tatopani station is the site of a large reactivated paleo-landslide that has experienced repeated failures. The Tatopani station is downslope from the amphitheater-like landslide scar and is constructed on distal landslide debris in a position vulnerable to future landslide and fluvial erosion hazards. We carried out detailed field investigations to document different types of geohazards around the station and present an evolutionary model for past and present landslide development. In addition, a simple numerical model was constructed to evaluate the stability of the large paleo-landslide body under different earthquake conditions. Simulated results suggest that the paleo-landslide body is stable without seismic loading. However, the large paleo-landslide will be remobilized again by large slope failures if the PGA of future earthquake exceeds 0.35 g. We suggest that the results presented in this paper should be taken into consideration during earthquake-resistant design of the border station and other infrastructural development along the Bhote Koshi Valley. [ABSTRACT FROM AUTHOR]