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One of the primary tasks for effective disaster relief after a catastrophic earthquake is robust communication. In this paper, we propose a simple logistic method based on two-parameter sets of geology and building structure for the failure prediction of the base stations in post-earthquake. Using the post-earthquake base station data in Sichuan, China, the prediction results are 96.7% and 90% for the two-parameter sets and all parameter sets, respectively, and 93.3% for the neural network method sets. The results show that the two-parameter method outweighs the whole parameter set logistic method and the neural network prediction and can effectively improve the accuracy of the prediction. The weight parameters of two-parameter set by the actual field data significantly show that the failure of base stations after earthquake is mainly due to the geological differences where the base stations are located. It can be envisioned that if the geological distribution between the earthquake source and the base station is parameterized, the multi-parameter sets logistic method can not only effectively solve the failure prediction after earthquakes and the evaluation of communication base stations under complex conditions, but also provide site selection evaluation for the construction of civil buildings and power grid towers in earthquake-prone areas. [ABSTRACT FROM AUTHOR]

A World Natural Heritage Site, Jiuzhaigou, is the first nature reserve in China whose primary purpose is to protect natural scenery. On August 8, 2017, a Ms 7.0 earthquake caused many unstable slopes in Jiuzhaigou, Sichuan Province, China. In the extreme storm conditions that follow, the unstable slopes tend to develop into potential landslides, which can cause many casualties and property losses in scenic areas. Sentinel-1A ascending orbit data were obtained in this paper to establish a SAR database. The large-scale deformation rate map of the study area was obtained using a small baseline set InSAR technology. The potential landslides in the deformation area are preliminarily confirmed with remote sensing interpretation. The field verification is further carried out by studying the deformation information of the characteristic points on the potential landslides. The results show that 13 deformation zones were preliminarily identified, and three typical deformation zones were selected for coupling verification and identified as potential landslides. At the same time, further analysis shows that the four potential landslides have been in continuous linear deformation for a long time since the earthquake, posing a severe threat to the safety of local people's lives and property. The research results provide a reference for the early identification and warning of potential landslides in earthquake-prone regions. [ABSTRACT FROM AUTHOR]

Background: On September 5, 2022, an Ms 6.8 earthquake occurred in Luding County, Ganzi Tibetan Autonomous Prefecture, Sichuan, China. The casualties and economic losses caused by the earthquake are huge. Most of the landslides triggered by this earthquake are small and medium-sized rock collapses and destructive debris flows, with a small number of large-scale landslides. Results: There are 5007 coseismic landslides in the Luding earthquake VII-degree area and above, with a total area of 17.36 km2. The landslides are generally distributed along the NW-SE direction. The highest landslide area density is 13.8%, and the highest point density of the landslide is 35.73 km2. High-density area is mainly concentrated in the IX-degree area and the northeast side of the seismogenic fault. Coseismic landslides are more likely to develop in the area with the slope more than 40°, the slope direction of 67.5-112.5 degree, and vegetation coverage of 40–50%. More landslides are developed in granite areas and forest areas. The closer distance to active faults, the more the coseismic landslides develop. The correlation between coseismic landslide development and the distance from the active faults is better than that between coseismic landslide development and the distance from the seismogenic faults. Conclusion: The landslide database used in this paper is the most perfect at present, and the research results have also been verified by fieldwork. This is also the first applied study of this landslide inventory, which indirectly confirmed the accuracy of the inventory. The results obtained in the manuscript will provide an important guideline for future disaster prevention and mitigation in southwest China. [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 geological activity in Sichuan and Yunnan of China is intense, and large earthquakes such as the Tonghai earthquake in 1970 have caused huge casualties and economic losses. Therefore, it is significant to reduce the long-period earthquake damage of dams and high-rise buildings to reproduce the near-fault long-period ground motion characteristics of the Tonghai earthquake. In this paper, the finite difference method is used to predict the long-period characteristics of the Tonghai Ms 7.8 earthquake. Considering the uncertainty of the initial fracture point, number of asperities, and slip angle, 18 seismic scenarios are established. The predicted results are verified by comparing intensity, attenuation relation and pulse probability distribution. At the same time, based on the velocity pulse recognition method, the pulse probability distribution of the near-field is obtained. We selected six seismic scenarios with high probability from 18 seismic scenarios. Our results show that the spatial distribution and pulse probability distribution of near-field simulated ground motion is significantly affected by the initial rupture positions. After the characteristics of the largest asperity on the fault are determined, the remaining asperities have limited influence on the spatial distribution of simulated ground motion. This study expands the application scope of the finite difference method, which can simulate the seismic intensity characteristics of destructive earthquakes in areas with few seismic records. [ABSTRACT FROM AUTHOR]

Slow-moving landslide-prone areas (SLAs) are unstable objects on the terrestrial surface that can collapse rapidly when provoked by earthquakes, leading to infrastructure damage. It is critical to identify SLAs prior to earthquake events and assess their hazard-causing probabilities when triggered. An assessment approach of earthquake-triggered geohazards is proposed in this paper by combining interferometric synthetic aperture radar (InSAR) derived SLAs and geological and geomorphological factors. Taking the Ms6.8 Luding earthquake, which occurred in the Sichuan Province of southwestern China on September 5, 2022, as an example, 1320 scenes of Sentinel-1 SAR data in western Sichuan were processed using the small baseline subset (SBAS) InSAR technique before the earthquake. After the earthquake, hazard probability assessment was performed in real-time by filtering the SLAs using a spatial analysis technique with geological and geomorphological factors, e.g., real-time peak ground acceleration (PGA), slope, distance to fault (DTF), and distance to the river (DTR) data. The results show that 11 SLAs were classified into high-risk zones. As verified by the Luding co-seismic landslide dataset from visual interpretation of optical remote sensing images, 142 coseismic landslides were triggered by the earthquake in these high-risk regions. In these areas, an ancient landslide, with high pre-earthquake displacement rates (−50 mm/year) on the scarp was reactivated under the Luding earthquake forces. This method can provide a scientific tool for disaster mitigation and rapid response emergency management. [ABSTRACT FROM AUTHOR]

A Mw 6.6 earthquake struck Luding county, in Sichuan province of China on September 5, 2022, causing severe damage of nearby infrastructures. The earthquake indicates an awakening of southeast branch of Xianshuihe fault since the last 1973 Mw 7.6 Luhuo earthquake in Sichuan, thus attracting attention from the public. A physics-based method, combining spectral element method (SEM) and finite element method (FEM), was presented in this paper to investigate the correlation between near-fault motions and response of a road tunnel, which has a closest distance of about 6.0 km to the fault. This method allows to incorporate the rupture details, geological irregularity, 3D velocity structure, as well as the underground tunnel. The ground motions simulated by SEM were validated by comparison to specific station records and empirical ground motion model (GMM), which were subsequently input into the tunnel to obtain its axial deformation and sectional inner forces. Parametric study on tunnel alignment was conducted, and wavelet transformation was used to extract dynamic pulses from the ground motions. The results show that the tunnel response is remarkably affected by dynamic pulse directivity, and the axial forces could be dominated by permanent fault displacement for tunnel of the strike-normal alignment. [ABSTRACT FROM AUTHOR]

Seismic risk estimation for urban building clusters is essential when developing regional seismic resilience models. A masonry structure is a type of building with a large stock, broad applicability, and simplified construction technology. The traditional seismic intensity measures and fuzzy quantification of structural vulnerability levels result in low accuracy in estimating and predicting seismic damage to masonry structure clusters. This paper proposes a method for evaluating bivariate seismic intensity measure. Nonlinear dynamic and spectral analyses were conducted on real acceleration records monitored by ten stations during the Wenchuan earthquake in Sichuan, China, on May 12, 2008. The outdated seismic vulnerability level of masonry structures is updated, and an optimized structural seismic risk model based on the seismic damage database of 2407 masonry structures in Dujiangyan city under the influence of the Wenchuan earthquake is established. An innovative seismic risk membership index algorithm was developed, and a vulnerability curve was generated for masonry structures considering multiple risk membership indices. An improved seismic risk index calculation function is proposed using the proposed updated vulnerability level, and the seismic risk index curve and stripe model of typical urban masonry building clusters are established. According to the field investigation of the actual structures in Dujiangyan city affected by the Wenchuan earthquake, the typical failure features and disaster mechanism of masonry structures are reported and analysed, and measures and methods to improve and enhance the seismic capacity of such buildings are proposed. The developed seismic risk model for urban masonry structures can contribute positively to the development of relatively accurate seismic resilience models for urban buildings and can improve the accuracy of seismic risk estimation for masonry structures. [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]

On August 20, 2019, at 2 a.m., a disastrous debris flow occurred in Chediguan gully in Yinxing town, China. The debris flow destroyed the drainage groove and the bridge at the exit of the gully. In addition, the debris flow temporarily blocked the Minjiang River during the flood peak, flooding the Taipingyi hydropower station 200 m upstream and leaving two plant workers missing. To further understand the activity of the debris flow after the Wenchuan earthquake, the characteristics of this debris flow event were studied. Eleven years after the Wenchuan earthquake, a disastrous debris flow still occurred in the Chediguan catchment, causing more severe losses than those of earlier debris flows. In this paper, the formation mechanism and dynamic characteristics of this debris flow event are analysed based on a drone survey, high-definition remote sensing interpretations and other means. The catastrophic debris flow event indicates that debris flows in the Wenchuan earthquake area are still active. A large amount of dredging work in the main gully could effectively reduce the debris flow risk in the gully. In addition, it is also important to repair or rebuild damaged mitigation measures and to establish a real-time monitoring and early warning system for the high-risk gully. [ABSTRACT FROM AUTHOR]

Due to China's exposure and susceptibility to natural hazards, it is important for governments and aid agencies to have tools that enable effective post-disaster livelihood recovery in creating self-sufficiency for the affected population. This paper introduces a framework of critical components that constitute a successful livelihood recovery by studying the perceptions and perspectives of those affected by the 2013 Lushan earthquake in Sichuan Province. A mixed method, namely a pilot study, questionnaire survey and interviews, was used. While the populations surveyed valued the employment benefits of creating new market and economic sectors in areas where rural farming was predominant prior to the earthquake, they considered that recovery of their housing was most essential for livelihood diversification. External assistance was also regarded highly in assisting with livelihood recovery, in which family ties and social connections seemed to have played a larger role than that of government agencies and NGOs. Lastly, the results highlighted that a goal of livelihood recovery cannot be achieved without individual well-being being considered, in relation to people's perceptions about quality of life and their physical and mental health. This paper aims to assist the Chinese policy makers and practitioners in disaster recovery in setting an agenda of preparing for livelihood recovery in peace times, or of post-disaster recovery planning should a disaster event occurs so that the economic impact and livelihood burdens of those affected can be effectively mitigated. [ABSTRACT FROM AUTHOR]

Maoxian Country in Sichuan Province, China is a quake-prone mountainous area. Within 300 km of it, there have been more than ten strong earthquakes higher than Ms6.0 on record. The nearest one is the Diexi Earthquake of 1933, 8.7 km from Maoxian County. A catastrophic scale landslide, the Xinmo landslide, took place on the steep cataclinal slope of Xinmo Village on June 24, 2017. Shear failure happened to the phyllite layer of rich fissures during the landslide. In this paper, shaking table tests have been conducted on the Xinmo landslide as a prototype, and a non-contact deformation measurement based on the digital image correlation (DIC) technique has been made to analyze the dynamic response and deformation of the slope under accumulated seismic actions. As the results, stress amplification is found at the end of joints on the potential slide face. Failure starting from the middle of the potential slide face in the beginning extends upwards and downwards along the face, and leads to a steep tension crack on the top of the slope and a buckling failure of radial-arc cracks at the foot. A semi-steep radial crack in buckling part has a shear failure. The tensile stress amplification on the discontinuous face contributes to the failure accumulation of it and asymptotic failure of the slope. It proposed that the closure and downward displacement of tensile crack on the top of slope, buckling phenomenon at the foot of slope and shear failure of semi-steep crack are all the bad omens of landsliding. [ABSTRACT FROM AUTHOR]

China is one of the countries most affected by earthquakes. Improving public cognition and response to earthquake disaster (EDCR) is an effective means to reduce seismic risk and losses. The 2013 Lushan earthquake area was also stricken by the 2008 Wenchuan earthquake. Most of the residents in this area have been affected by both earthquakes, which provides a rare opportunity to gain insight into the interaction between public's EDCR and their earthquake disaster experience. Using a questionnaire survey on over 200 local residents selected by stratified sampling method, this paper investigates the public's cognition and response capability with regard to earthquake disaster in the 2013 Mw6.6 Lushan earthquake area, Sichuan Province, China, with a particular emphasis on exploration on the relationship between people's earthquake disaster experience and their disaster cognition and response behaviors. The results show that the overall EDCR level of local residents is moderate—their average cognition and response score for earthquake disaster is only 0.60. The number of earthquakes experienced, education, and family income level are the three most important factors that significantly impact an individual's overall EDCR capability. Those who have experienced more earthquakes better adapt to the impacts of disaster. Especially, the experience learned from the 2008 Mw7.9 Wenchuan earthquake played a positive role in the cognition and response of the public to the 2013 Lushan earthquake. In addition, people with higher education could master more knowledge of earthquake disaster and better control their emotions. Similarly, respondents with a higher family income had more resources and ways to engage in more reasonable response behaviors to manage disaster effects. Based on these findings, it is suggested that local policy-makers implement targeted earthquake disaster education and knowledge dissemination strategies, especially develop and expand various experiential learning modes (e.g., emergency exercise/drilling, situational learning, virtual reality, scenario approach, safety/disaster experience center, participatory activities) for the local public and beyond to more effectively strengthen their cognition of disaster and response capability. [ABSTRACT FROM AUTHOR]

The MS8.0 earthquake that occurred in Wenchuan, Sichuan in 2008 provides an important case for the study of operational earthquake forecasting and short-term aftershock forecasting of major disaster-inducing earthquakes in China. This paper focuses on the comparative study of the applicability of the epidemic-type aftershock sequence (ETAS) model, the Reasenberg–Jones (R–J) model and the Omi–R–J model, which are widely adopted internationally for short-term aftershock forecasting and seismic hazard mitigation strategy research. We compare the stability of model parameters and aftershock occurrence rate forecasting, and evaluate the effectiveness of forecasting using the N-test and T-test with multiple time windows. The results show that the sequence parameters of the ETAS model, the R–J model and the Omi–R–J model tend to stabilize after 15.50, 15.50 and 6.00 days following the earthquake respectively, and the attenuation of the Wenchuan MS8.0 earthquake is rather normal. Compared to the ETAS model and the R–J model, the Omi–R–J model obtain steadier model parameters in a shorter time with significantly smaller parameters pORJ, cORJ, bORJ and standard deviations. Among the three models, the overall aftershock occurrence rate forecasted by the R–J model is the highest, followed by the Omi–R–J model, while that of the ETAS model is the lowest. N-test results show overall forecasting effectiveness of 93.8, 80.7 and 97.7% for the ETAS, R–J and Omi–R–J models, respectively, with the ETAS and Omi–R–J models superior to the R–J model, and the Omi–R–J model slightly better than the ETAS model. The overall "information gain per earthquake" calculation results show that the ETAS model is superior to the Omi–R–J and R–J models, while the Omi–R–J model is better than the R–J model; thus the combined use of the ETAS and Omi–R–J models by focusing on their respective strengths might ensure optimal performance. These "maneuverable" forecasting approaches to short-term aftershock model forecasting will play a vital role in efficient post-disaster relief, emergency management decision-making and post-disaster reconstruction. [ABSTRACT FROM AUTHOR]

On April 20, 2013, a Mw 6.6 earthquake struck Lushan County of Sichuan Province, China, about 80 km southwest of the epicenter of the 12 May 2008 Wenchuan Mw 7.9 event. It triggered a large number of landslides in a broad area, causing causality and injuries and damages to roads, drains, dwellings, and infrastructures. Field investigations of coseismic landslides provide a basis for better understanding and illustrating the spatial distributions and hazards related to the Lushan earthquake-triggered landslides. Therefore, this paper presents results of field investigations of the Lushan earthquake-triggered landslides, which can be classified into two main categories of disrupted landslides and coherent landslides, and constitutes seven types. The disrupted landslides include five types: rock falls, rock slides, rock avalanches, soil falls, and soil slides; and the coherent landslides have two types: soil slumps and slow earth flows. All of the seven types of landslides can be observed in many field photos, aerial photographs, and/or satellite images. Among them, seven typical large-scale landslides, distributed in a northeast trending line consistent with the Shuangshi-Dachuan fault, which is presumably related with the earthquake, are described in detail. We prepared an original, emergency-based coseismic landslide inventory map based on visual interpretation of available post-earthquake aerial photographs and pre-earthquake satellite images, combined with results from emergency-based field investigations. The original inventory map registered 3884 landslides. Later, 11,761 more landslides were identified by much more careful and time-consuming visual interpretation based on the same aerial photographs and satellite images. Subsequently, all the 15,645 coseismic landslides were correlated with six common landslide impact factors, including elevation, slope angle, slope aspect, topographic position, stratum/lithology, and peak ground accumulation (PGA). These observational and compiled coseismic landslide data allow us to make subsequent compiling of a detailed and completed landslide inventory by visual interpretation of remote sensing images as well as further studies of landslides induced by the Lushan earthquake. [ABSTRACT FROM AUTHOR]

The purpose of this work is to carry out seismically induced landslide probabilistic hazard mapping for future seismic scenarios of Aba Prefecture and Chengdu Plain region, Sichuan Province, China. Nine earthquake events that occurred in the regions and neighboring areas are selected, which include a total of 251,260 landslide records. This work used 12 influencing factors including elevation, slope, aspect, relief, topographic wetness index (TWI), topographic position index (TPI), peak ground motion, distance to active faults, vegetation coverage, distance to roads, lithology, and annual rainfall to establish the LR model. Based on the probabilistic seismic hazard analysis (PSHA) method, the distribution of predicted seismic motion under four earthquake scenarios is calculated including frequent, occasional, rare, and very rare earthquake occurrence. Using the PGA distribution of the four scenarios as input peak ground motion parameters, we calculated the occurrence probability of coseismic landslides in the entire Aba Prefecture and Chengdu Plain region under the action of different ground motions. The result shows that the high-hazard areas are mainly concentrated in the Longmenshan fault zone, and the southern area of Kangding is also a potential high-hazard area for landsliding. Meanwhile, as the probability of exceedance decreases, the probability of corresponding earthquake-induced landslides hazard probability and the area of high-hazard regions also significantly increase. Especially, the Pengguan complex rock mass in the southwest of the Longmenshan fault zone is the potential high-hazard area for coseismic landslides. Highlights: Establishing a coseismic landslides evaluation model suitable for Aba Prefecture and Chengdu Plain region. Calculating the occurrence probability of coseismic landslides under different peak ground motions. [ABSTRACT FROM AUTHOR]

Earthquakes that occur in a mountainous region can trigger a mass of landslides (ETL), and these hazards can cause relatively heavy casualties. Compared with other evaluation models and methods, quantification theory I is a multivariate statistical approach that can simultaneously process qualitative and quantitative variables. On the basis of the ETL features and the influencing factors, in this paper, we select lithology, slope gradient, slope height, slope structure, distance to seismogenic fault, hanging wall/footwall of the seismogenic fault, and rock integrity, a total of seven impact factors, as the assessment index. By randomly selecting 128 single slopes in an intense seismic area as the samples, we develop an assessment model and apply it to investigate the regional stability of the Jushui River basin to prove its applicability. Moreover, this method calculates the factor weight; this can also prove the method through a comparison with the existing research results obtained using other methods. [ABSTRACT FROM AUTHOR]

On September 5, 2022, a strong MS6.8 earthquake struck the Luding area in the Kangding-Moxi segment of the Xianshuihe fault zone, which is the northern boundary of the Sichuan-Yunnan rhombic block, causing considerable casualties. The Bamei-Kangding segment of the Xianshuihe fault zone, which is located only tens of kilometers away from the Luding earthquake, has hosted frequent moderate to strong earthquakes in history and is a dangerous earthquake-prone zone. Therefore, it is critical to investigate the regional seismogenic environment for strong earthquakes and to evaluate the impact of the Luding earthquake in this area. For this purpose, we deployed a dense seismic array comprising over 200 short-period nodes in this region from July to August, 2022 and acquired seismic ambient noise for over 30 days. Using the collected data, we conducted surface wave tomography and obtained a high-resolution 3-D shear wave velocity model for the regional shallow crust down to 8 km in depth. The key findings include: (1) the Bamei-Kangding segment of the Xianshuihe fault zone exhibits widespread stripped low-velocity anomalies, suggesting shear movements at a relatively high temperature of the Xianshuihe fault zone; the Zheduoshan granitic pluton situated between the Zheduotang and southern Selaha faults shows a distinct low-velocity anomaly, which may be attributed to the localized high-temperature anomaly resulted by a deep magmatic heat source and the recent rapid uplift of the Zheduoshan area; (2) a ten-kilometer-wide high velocity body found below 4 km in depth near the Zhonggu area in the Bamei segment coincides with the seismic gap of moderate to strong earthquakes in this region, suggesting that the high velocity body may act as a seismic barrier; (3) the heterogeneity of the velocity structure along the Bamei-Kangding segment of the Xianshuihe fault zone corresponds to the regional changes in temperature, which reveals the reason for the spatially varying seismogenic potential in this segment; especially, the Selaha and Zheduotang faults which are located along the boundaries between the high and low velocity anomalies may possess considerable seismogenic potential; (4) the Coulomb failure stress calculations indicate that the Luding earthquake has imposed nontrivial stress loading in the Bamei-Kangding segment, and may shorten the earthquake recurrence intervals of the southern Selaha fault, the Zheduotang fault, and the Xuemenkan segment of the Xianshuihe fault zone. Thus, the Luding earthquake may potentially pose threats to the Sichuan-Xizang railway passing through this region. [ABSTRACT FROM AUTHOR]

On September 5, 2022 (local time), a magnitude 6.6 earthquake was reported to have occurred in Luding County, Sichuan Province, Southwest China. In this simulation, a widely used stochastic finite-fault model was used to analyze how the source models affect the near-fault earthquake ground motion simulations of the 2022 Mw 6.6 Luding earthquake in China. Seven different slip models, one of them obtained from common fault parameters and random distributed slip amount, were used to yield the best match with the recordings. The simulated earthquake ground motions calculated in the frequency band of 0.05–20 Hz were compared with the observed values in both the time and frequency domains. Twelve acceleration observation stations located near the fault plane were selected in our simulation for comparison. The average H/V curves were estimated using the available acceleration records to consider the local site effect at each selected station. The research results indicate that none of the source models adopted in this study fully estimate the observed values at all the selected ground-motion stations. The simulated values of some slip models underestimate the level of the Fourier amplitude spectrum at frequencies above 6 Hz. The underestimation may be attributed to the directivity effect, which may produce a higher amplitude of observed ground motion in the high-frequency band. All the slip models show similar average model deviations except for the random slip model. Finally, the peak ground accelerations and peak ground velocities were predicted at these selected near-fault observation stations. The results indicate that the peak accelerations and velocities obtained from seven slip models correlate well with each other, but are slightly lower than the recorded values at most stations. In addition, the synthetized results calculated from the random and inverted slip models can be the same level only if a greater stress drop is adopted in the random model. [ABSTRACT FROM AUTHOR]

Although the Sichuan basin is a stable block with low historical seismicity, the Suining M5.0 earthquake on January 31, 2010 occurred near the center of the basin, causing casualty and substantial damage. Previous studies have shown that the earthquake is very shallow and may occur in the sedimentary cover rocks, but its causative fault has not been identified. Based on local broadband seismic waveform data as well as a pair of ALOS PALSAR ascending orbit data, we explore the seismogenic mechanism via further constraining the source depth and the ruptured fault. The earthquake caused ground uplift in the southeast of the epicenter area, with a maximum line of sight displacement of about 13.6 cm, much larger than the displacement caused by a M5 earthquake at a typical depth of 10 km, which indicates that the earthquake is very shallow. Through joint inversion of seismic waveform and InSAR data, we obtain the moment magnitude of Suining earthquake as MW4.5, with the strike, dip, and rake of its fault plane as 17°, 66° and 90°, respectively, and the centroid depth less than 1 km, supporting that the earthquake occurred at the shallow part of a high angle thrust fault dipping to the southeast. It is further confirmed that the earthquake may be triggered by the diffusion of high-pressure fluid migrating from the underside gas reservoir. [ABSTRACT FROM AUTHOR]

On September 5, 2022, an Ms6.8 earthquake struck Luding County, Sichuan Province, China. Through creating a coseismic landslide prediction model, we obtained the spatial distribution of the triggered geological hazards immediately after the earthquake. Through collecting all available multi-source optical remote sensing images of the earthquake-affected area via UAV and satellite platforms, the exact information of coseismic landslide was achieved by pattern recognition and visual inspection. According to the current results, the Luding earthquake triggered 5336 landslides with a total area of 28.53km2. The spatial distribution of the coseismic landslides is correlated statistically to various seismic, terrain, and geological factors, to evaluate their susceptibility at regional scale and to identify the most typical characteristics of these failures. The results reveal that the coseismic landslides mainly occurred on the sides of the Xianshuihe fault (within 1.2 km) and Dadu River (within 0.5 km) in striped patterns. They are concentrated in the regions with an elevation range of 1000–1800 m, a slope range of 25–55°, and lithologies of acid plutonic rocks, mixed sedimentary rocks, and siliciclastic sedimentary rocks. Besides, the coseismic landslides of the Luding earthquake are smaller in size and shallower than those triggered by the 2008 Wenchuan earthquake and the 2017 Jiuzhaigou earthquake. Rapidly achieving the spatial locations and distribution patterns of the coseismic landslides enables to provide effective support and guidance to emergency rescue, risk mitigation, and reconstruction planning. [ABSTRACT FROM AUTHOR]

An M6.8 earthquake occurred in Luding, Sichuan Province, China, on September 5, 2022. Since towns and villages in the earthquake-stricken area are densely populated, the earthquake caused severe fatalities and economic losses. Rapid estimation of earthquake intensity and disaster losses is significantly important for post-earthquake emergency rescue, scientific anti-seismic deployment, and the reduction of casualties and economic losses. Therefore, we make a preliminary rapid estimation of the earthquake intensity and disaster losses in the aftermath of the Luding earthquake. The seismic intensity represents the distribution of earthquake disasters and the degree of ground damage and can be directly converted from the peak ground velocity (PGV) map. To obtain a reliable PGV distribution map of this earthquake, we combined the finite-fault model constrained by seismic observations, with the complex three-dimensional (3D) geological environment and topographical features to perform strong ground motion simulation. Then, we compared the consistency between the simulated ground motion waveforms and observations, indicating the plausibility and reliability of simulations. In addition, we transformed the PGV simulation results into intensity and obtained a physics-based map of the intensity distribution of the Luding earthquake. The maximum simulated intensity of this earthquake is IX, which is consistent with the maximum intensity determined from the post-earthquake field survey. Based on the simulated seismic intensity map of the Luding earthquake and the earthquake disaster loss estimation model, we rapidly estimated the death and economic losses caused by this earthquake. The estimated results show that the death toll caused by this earthquake is probably 50–300, with a mathematic expectation of 89. Thus the government should launch a Level II earthquake emergency response plan. The economic losses are likely to be 10–100 billion RMB, with a mathematical expectation of 23.205 billion RMB. Such seismic intensity simulations and rapid estimation of disaster losses are expected to provide a preliminary scientific reference for governments to carry out the targeted deployment of emergency rescue and post-disaster reconstruction. [ABSTRACT FROM AUTHOR]

The 2019 MS6.0 Changning earthquake occurred in the tectonically stable Sichuan Basin, where the epicenter and its adjacent areas are important shale gas and salt mine production fields, resulting in hot debates on whether the seismogenic mechanism of the 2019 Changning earthquake is related to human activities. As source characteristics and fluid pressure can provide important constraints on whether an earthquake is induced, we investigate the seismogenic mechanisms of the mainshock and 9 MW⩾4.0 aftershocks. In overall, the mainshock and the majority of the aftershocks are characterized by relatively shallow focal depths (1–4 km) and significant non-double-couple (non-DC) components. However, the mainshock and the aftershocks differ in two aspects: (1) the compensated-linear-vector-dipole components dominate the non-DC components of the mainshock, whereas the isotropic components dominate the most aftershocks; (2) the fluid overpressure of the mainshock is over 30 MPa, whereas the fluid overpressure of the most aftershocks is less than 10 MPa. Thus, we propose that the mainshock is triggered by weakened fault strength with long-term fluid injection, and that its large non-DC components are associated with complex rupture processes. Comparatively, the aftershocks may be triggered by postseismic stress transfer by combining the Coulomb failure stress changes in the poroelastic medium. Our results highlight the possible role of fluid in the occurrence of the Changning earthquake sequence. [ABSTRACT FROM AUTHOR]

In this study, the post-earthquake economic recovery of the most severely affected areas in the 2008 Wenchuan earthquake is analyzed. First, a new analysis method that uses the economic data in Sichuan Province as the comparison standard is proposed. Then, based on the economic data of the most severely affected areas and Sichuan Province from 2003 to 2019, the post-earthquake economic recovery of the most severely affected areas is analyzed, and the results of the analysis are compared with those of the synthetic control method and the gray prediction model. Finally, the recovery path and its influencing factors are analyzed. The main findings are as follows: (1) The recovery of the post-earthquake economy varies among regions. Only the GDP per capita of An County and Pengzhou City had recovered to the pre-earthquake level by 2019. (2) The proposed method is highly similar to the synthetic control method in determining the recovery process and recovery time of the post-earthquake economy but differs significantly from the gray prediction model in the results of the analysis of the long-run economic recovery. (3) The post-earthquake economic recovery of the most severely affected areas shows a variety of recovery paths. The rapid and gradual decrease in the normalized gross investment in fixed assets (GIFA) per capita after the reconstruction period led to the economic recovery of the most severely affected areas into different recovery paths, and the significant increase in the normalized GIFA per capita and normalized retail sales of consumer goods (RSCG) per capita may lead to economic recovery breaking the equilibrium state and entering a new recovery path. Some discussions on the comparison of the proposed method, the synthetic control method and gray prediction model are also given as well as the economic recovery path. [ABSTRACT FROM AUTHOR]

The occurrence of destructive earthquakes is a small probability event, that is, the seismic samples are extremely imbalanced, which increases the difficulty of earthquake prediction. The existing earthquake prediction methods rarely adopt sample imbalance technology, and the prediction results are not good enough. Therefore, this study proposes a novel immune optimization inspired Numerical Differential Artificial Natural Killer Cell Algorithm (NDANKA) for earthquake prediction. First, based on the signals collected by our developed Acoustic and Electromagnetic Testing All in one system (AETA), historical record and precursor data are combined as the data source of our proposed model; then, the numerical differential artificial-based natural killer cell method is adopted to construct time-series Synthetic Minority Over-sampling Technique; moreover, an artificial antigen presenting cell approach is introduced to predict earthquakes; finally, the stochastic gradient descent method is adopted to optimize the parameters of the proposed algorithm. Through experiments in Sichuan and surroundings, the results demonstrate that the proposed NDANKA outperforms the state-of-the-art earthquake prediction approaches. Meanwhile, a hypothesis testing is accomplished. [ABSTRACT FROM AUTHOR]

In the neo-deterministic seismic hazard assessment (NDSHA) evaluation, great-earthquake-prone areas (GEPAs) play an important role in defining the 'controlling earthquakes' or 'scenario earthquakes'. When considering great earthquakes, their finite rupture attributes, which contribute to determine the strong ground motions and intensities, have to be taken into account. For continental earthquakes in China, the great earthquakes are located mainly within the boundary zones of the 'tectonic blocks'. The 'tectonic block' model indicates the focal mechanisms and some finite rupture attributes of the great earthquakes within the boundary zones. Accordingly, in the NDSHA for China, it is both necessary and feasible for the GEPAs to consider the finite rupture attributes of great earthquakes. The Sichuan-Yunnan border in southwest China has been taken as an example to naturally develop the originally used circular shape of GEPAs into one with more degrees-of-freedom, better reflecting the possible rupture processes of the considered earthquakes. [ABSTRACT FROM AUTHOR]

In tectonically active steep mountain belts, such as those in west Sichuan in China, frequent landslide disasters can occur during the rainy season. High-locality landslides often initiate with the failure of fractured rock masses or regolith near the ridge of a high and steep slope. Often, these events occur suddenly in the sense that people downslope are caught by surprise. High-locality landslides can be destructive owing to the large momentum and entrainment potential of the moving mass. Increasing attention has been given to these events since the 2008 Wenchuan earthquake. Indeed, slope ridges are particularly susceptible of topographic amplification of the seismic shaking, resulting in mechanical weakening that predisposes them to enhanced weathering and rain-triggered failures years or decades after the mainshock. Risk reduction in such cases must begin with a systematic surveying of the ridges to identify criticalities. Then, quantitative (numerical) approaches must be used to evaluate volumes and describe the movement. Risk assessments can then be produced, and mitigations suggested. Here, we describe the Tonghua landslide in Li County, which is currently in a creeping stage but threatens critical infrastructures and dwellings. We monitored the site for 3 years and identified additional potentially unstable areas before performing physically based modeling and hazard zonation. Our results could be useful in decision-making for risk reduction. [ABSTRACT FROM AUTHOR]

With the development of interregional trade, a potential disaster that happens in one place could cause enormous economic losses in distant areas. Timely and comprehensive post-disaster assessments play a significant role in guiding disaster recovery, and for reconstruction and planning for future disaster risk reduction. In this study, we evaluate the post-disaster economic impacts due to Sichuan earthquake in 2008 and its regional and industrial spillover effects based on a Chinese multi-regional input–output table. The results show that the 2008 Sichuan earthquake caused around 1725 billion US dollars of value-added losses and 69.9 million people of employment losses. The Chemical industry in Guangdong and Zhejiang suffered severe value-added losses due to indirect effects through supply chains. Furthermore, public administration in Henan, Sichuan, and Guangdong suffered large employment losses. In general, we find that the economically less developed provinces are more susceptible to larger losses compared to the economically developed provinces. The results in this study can provide information for decision-makers to devise effective solutions on how to release relief funds and for dividing adaptation plans to avoid serious economic losses due to future disasters. [ABSTRACT FROM AUTHOR]

The results of using a technology for zoning hazardous faults developed at the Institute of Physics of the Earth based on natural stress data are presented. The source of these data is catalogs of earthquake focal mechanisms, while inversion of stresses from them is obtained by cataclastic analysis of discontinuous displacements. For the studied region, which includes China's largest provinces, Sichuan and Yunnan, stresses are reconstructed from a regional catalog of focal mechanisms of earthquakes with Mw = 2.0–6.0 for 1999‒2012. The ability to predict the state of faults is based on data on the normalized values of the isotropic and deviator components of the stress tensor. Two variants of fault zoning are presented, which resulted from application of the Drucker–Prager and the Mohr–Coulomb criteria characterizing the elastoplastic and brittle behavior of the crust, respectively. It is shown that the second approach yields better and more detailed information on the state along the active faults of the western Sichuan region. Analysis of the state of the Longmen Shan fold-and-thrust belt prior to the Wenchuan earthquake that occurred on May 12, 2008, showed that the distribution of Coulomb stresses along the fault with at least 70% of the length, and a high level of Coulomb stresses (>60% of the critical stresses) should be considered hazardous. Based on the tectonophysical zoning findings, more than 20 sites of active faults with lengths of 60–140 km have been identified in the studied region, which we consider as potential sources of strong earthquakes with magnitudes ≥7.0. [ABSTRACT FROM AUTHOR]

On 25 August 1933, a 7.5-magnitude earthquake struck the eastern margin of the Tibetan Plateau in Sichuan, China. The Diexi earthquake is among the largest known geohazard events worldwide and is frequently cited by those studying the effects of large earthquakes. And yet, the attention focused on this event has failed to deliver a clear picture of landslides and their geomorphic impacts—key attributes of the Diexi earthquake and its aftermath remain obscure and debated. By integrating present-day LiDAR topographic data with existing records (including studies published in Chinese), and a series of unique archival photographs (from 1910, 1920, and 1934), we present the first inventory of coseismic landslides from the epicentral region of this catastrophic 1933 event. We find that the earthquake-triggered landslides were mainly of shallow to deep rock/debris fall/avalanche type, containing mass detached from steep slopes at the top of the mountain ridge source. We reinterpreted three major landslide dams on the Minjiang River based on their geomorphology and sedimentology, and we reconstructed the processes of impoundment and the maximum area of the dammed lake that breached 45 days after the earthquake. Since 1933, we estimate that 43.15–47.68 million m3 of post-earthquake sediment has been delivered to valley floors from the erosion of the three landslide dams, with a sediment yield of up to 131.71 t km−2 year−1. Retrospective studies of the effects of historical earthquakes are challenging, but long-term observations like these are the cornerstone of emerging knowledge of earthquake-induced landsliding and related landscape response. [ABSTRACT FROM AUTHOR]

Enhanced debris flow activity observed after the 2008 Wenchuan earthquake, Sichuan Province, SW China, is still intense more than a decade since the earthquake. A heavy rainstorm on 20 August 2019 caused catastrophic debris flows in the epicentral area of the earthquake. By remote sensing imagery interpretation and field investigation, 13 debris flows were identified. An empirical rainfall threshold I-D model (intensity–duration) of post-seismic debris flows is established. Changing rainfall thresholds, characteristics, and initiation mechanisms of the 2019 debris flows were analyzed, which are different from the events that occurred in previous years. We find that the 2019 debris flows were mainly initiated by concentrated runoff erosion of sediments stored in tributary channels of catchments, with little contribution from the coseismic landslides and new hillslope failures. Differently, the major sediment supply of debris flows in previous years was mainly from the reactivation of coseismic landslide deposits. By analyzing the triggering rainfall of all recorded debris flows after the Wenchuan earthquake, we find that the rainfall threshold in 2019 is about 1/2–4/5 of the pre-earthquake value, and the I-D model we built can predict the 2019 debris flows successfully. Considering that there are still a large number of coseismic landslide deposits in the mountain catchments and the rainfall thresholds are slowly recovering, the post-seismic debris flows may last for a long period. [ABSTRACT FROM AUTHOR]

Landslides are recurrent geological phenomena on Earth that cause heavy casualties and property losses annually. In this study, we use the Vp-k stacking and nonlinear waveform inversion methods of high-frequency receiver functions extracted from local earthquakes, to sequentially invert Poisson's ratios and S-wave velocities of the Quaternary Xishancun landslide, which is composed of three segments, i.e., h1, h2, and h3 from bottom to top. Our results show that Poisson's ratio values are generally higher than 0.33 and that the S-wave velocities vary from 0.1 to 0.9 km s−1. High Poisson's ratios (>0.44) are mainly distributed in the juncture regions between different segments, as well as the western edge of h2. These zones show significant variation in landslide thickness and are potentially hazardous areas. Low velocities of 0.05–0.2 km s−1 with thicknesses of 10–30 m are widely observed in the lower layer of the landslide. The high Poisson's ratios and low-velocity layer may be related to water-rich materials in these areas. Our study suggests that the high-frequency receiver functions from local earthquakes can be used to delineate geotechnical structures, which is valuable for landslide stability analysis and hazard mitigation. [ABSTRACT FROM AUTHOR]

In recent years, a series of earthquakes have occurred in Sichuan province, southwest China. On April 20, 2013, 1013 landslides were triggered in the Lushan earthquake within the research area of 1215.87 km2. On August 8, 2017, 821 landslides were induced in the Jiuzhaigou earthquake within the study area of 541.61 km2. The slope, aspect, elevation, distance to the river, distance to fault, stratum lithology, curvature, and PGA as evaluation factors were chosen to research the distribution characteristics of coseismic landslides. The relationship between influence factors and distribution of coseismic landslides were analyzed using landslide area density (LAD), defined as the ratio between the coseismic landslides area and the total area under the specific classification of eight factors, and landslide number density (LND), interpreted as the number of landslides per square kilometer affected by an earthquake. Both the LAD and LND curves show the common correlations between distribution characteristics of coseismic landslides and the classification of eight factors. The high density of coseismic landslides was found at locations where the valley evolves from U-shaped to V-shaped, along slopes with an inclination between 20 and 50°. Due to the effect of river cutting erosion and human engineering activities, massive coseismic landslides appeared within the scope of 200 m from the river system. Eight hundred sixty small shallow coseismic landslides were found less than 3 km from the seismogenic fault in both earthquakes. Both concave and convex terrain has the same effect of promoting coseismic landslides. The strata of the Carboniferous and Cretaceous are more prone to coseismic landslides occurrence. In the event of another earthquake of similar magnitude in southwest China in the future, the research results can quickly predict the distribution of coseismic landslides and provide a scientific basis for emergency rescue. [ABSTRACT FROM AUTHOR]

This work aims to characterize the earthquake-triggered landslides (EQTLs) during the 2017 Jiuzhaigou earthquake and to describe the geological and geomorphological control of landslide hazards. The Jiuzhaigou-EQTLs were studied via field-based investigation and remote sensing techniques during few weeks immediately after the mainshock occurred. The Jiuzhaigou earthquake produced an 11.4-km2 landslide area with 5633 landslides, dominated by shallow disrupted landslides, rock falls, and rockslides/rock avalanche. Statistical analyses show that the Jiuzhaigou-EQTLs had low mobility with a modal apparent friction angle of 40–44°. The Jiuzhaigou-EQTLs mostly occurred at elevations of 2700–3500 m and below 900 m relative relief to the main riverbed, where small-scale landslides were situated at the lower to middle parts of hillslope and large-scale landslides were situated close to the ridge crests. Jiuzhaigou-EQTLs clustered on river valley-side at the upstream of Baihe River (Jiuzhai Paradise and Ganhaizi village), Rize gully, and Danzhu gully on the tectonically active region at the southwest side of seismogenic fault F2. Landslides are prone to failure on the carbonate rocks with anaclinal hillslopes, following the cataclinal and cata-plagioclinal hillslopes. Most Jiuzhaigou-EQTLs preferentially occur on the below low-level break line (L2) in V-shaped valley-side and between first-level (L2) and high-level break line (L1) in U-shaped valley-side formed from long-term paleo-glacier and river incision. We found that landslide frequency is determined by a combination of the earthquake source with ground deformation, slope distribution, and rock strength due to weathering and dissolution along the fractures. Ground surface deformation, rock type (strength), geological structures, and valley-side slope breaks dictated the Jiuzhaigou-EQTL distribution pattern and hazards. This study elucidates the roles that local conditions play in influencing the occurrence, distribution, and frequency of slope failures and provides a better understanding of EQTL phenomenon during the Jiuzhaigou earthquake. [ABSTRACT FROM AUTHOR]

This article explores the spatial differentiation and integration between the post-disaster victims and the indigenous peasants 8 years after a rapid off-site resettlement oriented by governments in New Beichuan. Data were broadly collected from placement documents, questionnaires, interviews and site measurement by empirical research and on-site investigation in 2014. The resettlement plan was introduced and analyzed for housing resettlement, open space systems, public facilities allocation and resettlement policies. Based on statistical analysis of the questionnaire data and observation on the usage of the built environment, problems with the spatial usage and mismatches between the specific spatial requirements and subjective planning intention of integration are analyzed and preliminary findings are shown. The results showed that the excessive pursuit of speed and deficiency in economically self-sustaining efforts might contribute to insufficient attention given to spatial, social and economic aspects and leads to inevitable and long-standing problems, such as housing quality problems, neighborhoods management and security concerns, contradictions between the housing layout and local living habits, different spatial usage preferences between the indigenous peasants and post-disaster migrants, and disequilibrium of public facility allocation. [ABSTRACT FROM AUTHOR]

An improved stochastic finite-fault method was used to simulate the Mw 6.6 earthquake that occurred on August 8, 2017, in Jiuzhaigou, Sichuan, China. A variation of the stochastic finite-fault method, considering the dynamic corner frequency, was used to overcome the corner frequency. It explains the effect of a given slip distribution on the corner frequency of each subfault. A comparison of the response spectra (damping ratio 5%), spectral ratio (simulated values/observed values), and model deviation demonstrated that the improved corner frequency performs well for the whole periods, especially in short periods from 0.2 to 1 s. Similarly, the revised duration model and the site-amplification factor were applied to simulate the ground motion during the Jiuzhaigou earthquake, and then the response spectra were obtained. The duration of the nine near-field station recordings matched well with the simulated ground motions, and the peak ground acceleration (PGA) of most of the stations matched well with the observed PGA. In the short periods (T < 1 s), a small difference is observed between the simulated response spectra and the observed spectra for most of the stations. However, the response spectra were overestimated within the period range (0.05–10 s). Generally, the simulated ground motions obtained by using the improved model matched well with the observed ground motions, which could be considered the basis for earthquake-resistant design during the postdisaster recovery and the structural dynamic analysis of the Jiuzhaigou region. [ABSTRACT FROM AUTHOR]

The Ya'an, Sichuan Mw 6.7 earthquake occurred on April 20, 2013. In this article, the stochastic finite-fault method (EXSIM) based on dynamic corner frequency, proposed by Motazedian and Atkinson (Bull Seismol Soc Am 95(3):995–1010, 2005), is validated to be an intelligible and productive approach for the generation of high-frequency strong ground motion. The validated model parameters were considered for the simulation at 31 selected stations, which are less than 200 km away from the fault. The input parameters included site condition, source term, and path term. The calibration of the input parameters, such as the stress drop, was achieved by using misfit functions between the observed PSA (pseudo-acceleration response spectra) and simulated PSA in the time domain. Some of the other parameters, such as distance-dependent duration, high-frequency attenuation parameter kappa, and local amplification functions, were calibrated by considering the observed recordings. In this study, we attempted to employ two different slip models for strong ground motion simulation, so that the influence on the simulation results can be revealed. Our results depicted that although the method cannot combine well, the directivity effects and the soil conditions are not adequately represented at individual stations, the synthetics satisfactorily match with the seismic characteristics regarding peak ground acceleration (PGA), response spectra, Fourier spectrum, and time history, for both the time and frequency range considered. The results also demonstrated that there is a slight difference between the simulation results of the two slip models. Finally, we compared the effects of different distance-dependent duration models for the simulated PGA. It illustrates that it is difficult to find a balance between the ground motion duration and PGA at stations with fault distance less than 20 km, which makes the duration and PGA to coincide well with the observed recordings. [ABSTRACT FROM AUTHOR]

We created a three-dimensional (3D) viscoelastic finite element model of the crust to study post-seismic influences of the Wenchuan earthquake, considering both the horizontal fragmentation and vertical strata of the crustal material in the Sichuan–Yunnan region, and the asymmetrical static displacement of hanging wall and footwall on the fault plane in relation to the earthquake. Results indicate that (1) a far-field accumulated horizontal deformation of approximately 0–20 mm occurred inside the Sichuan–Yunnan block, 10 years after Wenchuan earthquake, due to the medium's viscoelastic relaxation effect, and the deformation was greater in the north than in the south. (2) The far-field accumulated vertical deformation of the medium's viscoelastic relaxation in the Sichuan–Yunnan block was small (0–4 mm) during the same period. (3) A belt of high horizontal and vertical deformation gradients are evident along the Xianshuihe and East Kunlun faults. Coincidentally, several significant earthquakes (MS 5.4 Daofu 2010, MS 5.7 Luhuo 2011, MS 6.3 Kangding 2014 and MS 7.0 Jiuzhaigou 2017) were located on the belt described above. (4) The seismic activity of the faults of increasing Coulomb failure stress is stronger than that of other faults, generally. [ABSTRACT FROM AUTHOR]

The load/unload response ratio (LURR) method has been proposed to evaluate earthquake potential. This method can be used to investigate the regional stress–strain field change and fault instability associated with the preparation of a large earthquake. In this study, we explore the temporal and spatial evolution of the LURR anomalies before the M7.0 Jiuzhaigou earthquake that occurred on Aug. 8, 2017 in Sichuan Province. We calculate the LURR values by using Benioff strain of the small earthquakes within 100, 200, 300 and 500 km from the epicenter and 12 years prior to the main shock. The loading and unloading phases are determined by calculating the change of Coulomb failure stress caused by earth tide in the tectonically preferred slip direction on the fault surface of the major event. Results show that the LURR values remain at a low level for years until 2014 when the LURR values increase to an anomalously high level. Meanwhile, the magnitude of the anomalies decrease with the distance from the epicenter, and can hardly be observed within the 500-km radius. Combining with the spatial distribution of the LURR, we find that the development of anomalies before the mainshock can be divided into two stages: during the periods of 2014–2015, the significant anomalies were observed in the epicenter and its northwest region; and then in 2016, the anomalies were detected in the southeast area of the earthquake, which expanded around the Huya fault and finally reached the epicenter months before the mainshock. The earthquake is located at the intersection area of LURR anomalies of the two time periods, suggesting the generation of the Jiuzhaigou earthquake. [ABSTRACT FROM AUTHOR]

At 5:38:58 a.m. on June 24, 2017, a catastrophic rockslide avalanche occurred at the Xinmo village, Diexi town, Maoxian county, Sichuan Province, and the area could have been deeply affected by many strong earthquakes in history. The landslide killed 83 people and destroyed the whole village, with the runout horizontal distance of about 2800 m and the elevation difference of 1200 m, which was equivalent to a Fahrböschung of about 23°, and the accumulative volume reached nearly 18 million m3. The field investigation and preliminary analysis of landslide seismic signals indicated that, after sliding from the ridge crest, the rock mass continuously impacted and accumulated on the upper part of the slope, which caused the substrate, i.e., old rockslide accumulation, to slide and disintegrate. It was transformed rapidly into a pipeline-type debris avalanche that then turned into a fan-like debris flow due to the terrain, which also had the typical dynamic characteristics of high speed and long runout. However, in fact, as the cause and effect of the kinematic and dynamic processes of the Xinmo landslide is so complicated and difficult to understand, the Fast Lagrangian Analysis of Continua (FLAC) and the slope-stability analysis module of GeoStudio were firstly combined to analyze the failure process of the old rockslide accumulation body when suffering the added forces from the landslide. Then, the Engineering Discrete Element Method (EDEM) was used to simulate the runout behavior of the displaced landslide materials, the calculated velocity value of which was also compared with those using other dynamic modeling approaches (e.g., sled model, rheological model, and liquefied model). The results demonstrate that the dynamic characteristics and the kinetic type of the Xinmo landslide were successfully simulated. Besides, the velocity values simulated by EDEM and by the rheological model were close to the value of around 60 m/s based on the distance of debris avalanche and the corresponding duration recognized through landslide seismic signals. Also, their velocity variation curves with motion were rational. The above proposed method can be further applied for studies on early recognition and hazard zonation of similar large-scale rockslide avalanches in areas affected by strong earthquakes. [ABSTRACT FROM AUTHOR]

Jiuzhaigou is a world-heritage site located in the plateau area of Northwest Sichuan Province, China. Serious slope failures in the epicentral area were triggered by the Ms7.0 Jiuzhaigou earthquake occurred on August 8, 2017. The source areas of the hazards are usually concentrated near ridge crests, revealing the possible occurrence of ground motion amplification phenomena. To explore the role of the amplification of ground motions in the formation of earthquake-triggered slope failures, two seismometers were installed, on the next day after the main shock, at the bottom of the slope of Jubao Mountain near the seismogenic fault. The two monitoring sites are located at elevations of 1414 m (J1) and 1551 m (J2, the top of the mountain). Five aftershocks were recorded by the monitoring instruments. We compared the mean levels of the peak ground acceleration (PGA) observed at different locations, and investigated the directional variations in the shaking energy by analyzing the polar diagrams of the Arias intensity (Ia). Then, in order to identify the directional resonance phenomenon and their frequencies and amplification coefficients, we examined the horizontal-to-vertical spectral ratio (HVSR) and the standard spectral ratio (SSR). Polar diagrams of the Arias intensity (Ia) indicated that the site response of Jubao Mountain showed a pronounced directivity (in the EW direction) with shaking maxima near the hill top oriented orthogonally to the elongation of the relief. We observed an obvious resonance phenomenon at site J2 at relatively low frequencies (2.5–9 Hz) and very weak spectral amplifications at site J1 at high frequencies (5–15 Hz), which suggested that the predominant frequency of monitoring site J2 was obviously attenuated and that the difference in the spectra was related to the influences of the local-scale site conditions of the whole mountain. The results of spectral ratio analyses (HVSR and SSR) showed that the direction of resonance was concentrated around an EW orientation, and the amplification factors near the hill top were larger than 2. It suggests that geologic factors also play a significant role in the anisotropic amplifications affecting the tops of slopes besides the topographic effects. [ABSTRACT FROM AUTHOR]

In 2008, Wenchuan earthquake shook Sichuan Province in China. The questions of how to value the economic loss that would result if a catastrophe were to occur in Capital Beijing and how long the recovery period would last have long been topics of concern for the government and the public. This study envisions an earthquake similar to the Wenchuan earthquake occurring in Beijing and examines the differences in indirect economic loss and recovery periods between Beijing and the Wenchuan earthquake using the same loss rate. An improved input–output model is used to evaluate the indirect losses. The results show that (1) Beijing experiences greater indirect loss than Sichuan. When both regions suffer a direct loss of USD 100, Beijing suffers USD 12 more in indirect loss than does Sichuan. (2) The reconstruction period of Beijing is shortened by at least 5 months, and indirect loss is reduced by 27.1% if the assistance level increases from 120 to 150% of that provided to Sichuan. (3) High assistance efficiencies can effectively reduce total losses, but increasing the efficiency of strength is more efficient than improving the efficiency of time in Beijing. Five sectors in Beijing are firstly needed to be assisted to recover, which can help other sectors to recover more quickly and efficiently through industrial linkages. Dynamic assessment of indirect loss in this study may help the government better understand the quantitative impact of disasters and allocate assistance resources more efficiently in Beijing. [ABSTRACT FROM AUTHOR]

The April 20, 2013, Ms 7.0 Lushan Earthquake was a major earthquake that followed the Ms 8.0 Wenchuan Earthquake on May 12, 2008. Frequent earthquakes have caused heavy casualties and property loss in Western Sichuan. Earthquake disasters are often closely related to the amplification effect of ground motion. Studying the ground motion characteristics of near-surface geological structures helps to understand the distribution of potential earthquake disasters. In this study, we investigated ground motion amplification in the downtown area of Lushan using numerical simulation and aftershock data from the Lushan Earthquake. Using the Lushan earthquake aftershock data from nine seismic stations distributed in the area, the amplification effect of the sites was determined using the "reference site spectral ratio" method. The results show that the frequency of the ground motion amplification in the area was in the range 5–10 Hz, and the corresponding amplification peak was from 3 to 14. Among the study sites, the amplification (14 times) at L07 was the most prominent. To study further the amplification characteristics, shear-wave velocity models for the structures under these sites were established using passive-source Rayleigh surface-wave exploration. One-dimensional (1D) and two-dimensional (2D) seismic amplification effects were simulated using horizontally propagating shear-wave modeling. Except Site L07, the 1D simulation results of each site well reflected the variation feature of the seismic amplification on the frequency band below the observed peak frequency, although the overall simulated amplification peaks were smaller than the observed results. The 2D simulation of the remarkable amplification phenomenon at L07 was in better agreement with the observation result than was the 1D simulation, indicating that the seismic amplification in the Modong area is influenced by lateral variation of the Quaternary sediments. [ABSTRACT FROM AUTHOR]

Observation and research of rotational motions induced by earthquake has been ignored in the past decades due to the lack of understanding of important ground rotational motions and practical difficulty involved in directly measuring the rotational components. Currently, there is a paucity of methods to directly measure rotational motions in China. The present study attempts to discuss the possibility of obtaining seismic rotation from ground tilt data. The rotational motions generated by shear dislocation source are derived based on the displacement formula of elastic wavefields in the homogenous space. The characteristics of the three components of translational and rotational motions in near, intermediate, and far fields are compared and analyzed. Based on the corresponding relationship between the rotation and ground tilt on free surface boundary, a method to indirectly construct the rotational motions in the layered half space is obtained. Finally, the theoretical rotational motions generated by the Ms7.0 earthquake in Jiuzhaigou, Sichuan Province, on August 8, 2017 are calculated. The results indicate that the rotational motions generated by the Jiuzhaigou earthquake are concentrated in the vicinity of the epicenter (approximately 150 km) and mainly distributed in the area perpendicular to the fault strike. The existence of free surface boundary attenuates the total energy of the rotational field and especially in the direction of the dominant energy. The ground tilt data is compared with rotational motions in the layered half space, and the results indicate that theoretical rotations and actual ground tilt data are essentially consistent, especially in the far field region. Thus, it is possible to obtain horizontal components of rotation from ground tilt data, and this provides more information for a complete description of the motion characteristics of an underground medium. [ABSTRACT FROM AUTHOR]

On April 20, 2013, the Lushan M7.0 earthquake struck at the southern part of the Longmenshan fault in the eastern Tibetan Plateau, China. The shear-wave splitting in the crust indicates a connection between the direction of the principal crustal compressive stress and the fault orientation in the Longmenshan fault zone. Our relocation analysis of the aftershocks of the Lushan earthquake shows a gap between the location of the rupture zone of the Lushan M7.0 earthquake and that of the rupture zone of the Wenchuan M8.0 earthquake. We believe that stress levels in the crust at the rupture gap and its vicinity should be monitored in the immediate future. We suggest using controlled source borehole measurements for this purpose. [ABSTRACT FROM AUTHOR]

The Jinlong village landslide is located in Zitong County, Sichuan and approximately 150 km east of Wenchuan. The landslide has exhibited creep deformation for nearly 30 years. Field investigations indicated that the slope deformation was caused by the combined effects of unfavorable topographic and geological conditions and earthquakes. The sliding surface is along a contact between silty clay and mudstone. The Wenchuan earthquake accelerated the creep, causing bulging of the ground surface. Shear test results of the silty clay near the sliding surface indicated that the residual strength is consistent with the stability state of the landslide. The factors of safety were calculated using the limit equilibrium method (LEM) and the method of fast Lagrangian analysis of continua in two dimensions. The results using the LEM indicate that the stability is clearly affected by seismic shaking, and when the peak ground acceleration is 0.08 g, the slope reaches the limit state. The shear failure surface given by numerical simulation develops on the contact between the clay and silty mudstone, which confirmed the assumed sliding surfaces' location using the LEM. [ABSTRACT FROM AUTHOR]

The 2008 Wenchuan earthquake induced a large number of landslides, and a vast amount of loose landslide materials deposited on steep hill slopes or in channels. Such loose materials can become sources of deadly debris flows once triggered by storms. On 13 August 2010, a storm swept Yingxiu and its vicinity, triggering a catastrophic debris flow with a volume of 1.17 million m in Xiaojiagou Ravine. The debris flow buried 1,100 m of road, blocked a river and formed a debris flow barrier lake. A detailed field study was conducted to understand the initiation mechanisms and runout characteristics of this debris flow. Two types of debris flows are identified, namely hill-slope debris flow and channelized debris flow. The hill-slope debris flow was triggered in the forms of firehose effect, rilling and landsliding, whereas the channelized debris flow was triggered in the form of channel-bed failure. This debris flow was a water-rock flow since most particles were gravel, cobble or larger rocks and the fraction of silt and clay was less than 2%. Grain contact friction, pore-pressure effects and inertial grain collision were the three most important physical interactions within the debris flow. Such interactions yielded a smaller runout distance (593 m) compared with those of mud-rock flows of similar size. [ABSTRACT FROM AUTHOR]

On 12 May 2008, an earthquake with a magnitude of 8.0 on the Richter scale hit Wenchuan, China. In the aftermath of this natural disaster, Chinese dental professionals actively participated in the first emergency medical response team, definitive dental treatment, oral health services and education, and the recovery of local oral care infrastructure and resources. Learning from the experience and first-hand data of the Wenchuan earthquake, dental professionals can increase their awareness of the importance of collaborative emergency response health services in mass casualty events. Further research and emphasis is needed to encourage the participation of dental professionals in disaster preparation training and practice. [ABSTRACT FROM AUTHOR]

Western Sichuan is among the most seismically active regions in southwestern China and is characterized by frequent strong (M ≥ 6.5) earthquakes, mainly along the Xianshuihe fault zone. Historical and instrumental seismicity show a temporal pattern of active periods separated by inactive ones, while in space a remarkable epicenter migration has been observed. During the last active period starting in 1893, the sinistral strike–slip Xianshuihe fault of 350 km total length, was entirely broken with the epicenters of successive strong earthquakes migrating along its strike. This pattern is investigated by resolving changes of Coulomb failure function (ΔCFF) since 1893 and hence the evolution of the stress field in the area during the last 110 years. Coulomb stress changes were calculated assuming that earthquakes can be modeled as static dislocations in an elastic halfspace, and taking into account both the coseismic slip in strong (M ≥ 6.5) earthquakes and the slow tectonic stress buildup associated with major fault segments. The stress change calculations were performed for faults of strike, dip, and rake appropriate to the strong events. We evaluate whether these stress changes brought a given strong earthquake closer to, or sent it farther from, failure. It was found that all strong earthquakes, and moreover, the majority of smaller events for which reliable fault plane solutions are available, have occurred on stress–enhanced fault segments providing a convincing case in which Coulomb stress modeling gives insight into the temporal and spatial manifestation of seismic activity. We extend the stress calculations to the year 2025 and provide an assessment for future seismic hazard by identifying the fault segments that are possible sites of future strong earthquakes. [ABSTRACT FROM AUTHOR]