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On July 18, 2023, on the K54 + 670 ~ K54 + 700 section of G351 National Highway in Baoxing County, Ya'an City, Sichuan Province, the rock mass (30° 25′ 4.8″ N, 102° 50′ 21.84″ E) located at the entrance of Leying in the Guanyinyan Open-cut Tunnel and affected by Lushan earthquakes and heavy rainfall factors suffered a rock mass collapse accident (hereinafter referred to as the Guanyinyan collapse, or collapse). It is a typical delayed rock mass collapse event that occurs under the influences of historical earthquake sequences and rainy season rainfall. The collapsed area has the maximum thickness close to 2 m, and a volume of about 1500–2000 m3. Some collapsed rocks have rolled into the interior of the tunnel and the riverbed, and boulders with a diameter of nearly 5 m have been found in the river channel. Most of the collapsed material accumulates on the road, approximately 1260 m3, burying some 30 m of the highway, severely affecting the normal use thereof. This article used a detailed field investigation, unmanned aerial vehicle (UAV) photogrammetry, historical image comparison, and numerical simulation methods to gain a deeper understanding of the engineering geology and historical earthquake situation in the study area. A three-dimensional site model was also established to identify the rock mass structural joints and accumulation conditions in the collapsed area, and the deterioration and fracture factors and historical evolution process of the dangerous rock mass were briefly analyzed, Finally, a comparative analysis was conducted between the simulated results using the three-dimensional finite discrete element method (FDEM) and the dynamic process as evinced by of real-time video footage. The collapse mainly experienced a local instability stage, stress adjustment stage, and overall collapse-accumulation stage. The further understanding of its motion characteristics and energy evolution can provide a basis for subsequent protection design and also a valuable experience for similar research in the region. [ABSTRACT FROM AUTHOR]

This paper considers setting different dips for different sub-faults to fit the actual rupture situation based on the fault rupture of the 2013 Lushan MS7.0 earthquake. Meanwhile, combined with the coseismic GNSS data of the Lushan earthquake, the source parameters and sliding distribution of the Lushan earthquake fault are inversed. Firstly, we use the gradient based optimizer (GBO) in nonlinear inversion to obtain the source parameters of this seismic fault. The inversion results indicate that the strike of the fault is 206.52°, the dip is 44.10°, the length is 21.92 km, and the depth is 12.79 km. To refine the sliding distribution of the seismic fault, the seismic fault is divided into 3 × 3 sub-faults. Then, we fix the central sub-fault dip of 44.10°; the dip of other sub-faults is obtained by iteration. After that, the model is further divided into a fault layer model composed of 23 × 19 sub fault slices, and using the Matlab fitting function is used to fit the dip of the 23 × 19 sub faults. Finally, the Lushan seismic fault plane is established as a shovel structure with steep upper and gentle lower, steep south and gentle north. The slip distribution inversion results indicate that the depth of the slip peak is 13 km, the corresponding maximum slip momentum is 0.67 m, the seismic moment is 1.10 × 1019 N·m and the corresponding moment magnitude is MW6.66. The results above are consistent with the research results of seismology.

On 1 June 2022, a magnitude 6.1 earthquake struck the southern segment of the Longmenshan fault zone on the eastern edge of the Tibetan Plateau, once again causing casualties and economic losses. Understanding the deep-seated dynamic mechanisms that lead to seismic events in the Lushan earthquake area and assessing the potential hazards in seismic gap areas are of significant importance. In this study, we utilized 118 magnetotelluric datasets collected from the Lushan earthquake area and employed three-dimensional electromagnetic inversion with topographic considerations to characterize the deep-seated three-dimensional resistivity structure of the Lushan earthquake area. The results reveal that the Shuangshi–Dachuan fault in the Lushan earthquake area can be divided into two relatively low-resistivity zones: a western zone dipping southeastward and an eastern zone with a steeper slightly northwestern dip. These two zones intersect at a depth of approximately 20 km, forming an extensional pattern resembling a "Y" shape. The epicenters of both the 2013 and 2022 Lushan earthquakes are primarily located in the upper constricted portion of the pocket-like low-resistivity body at depth. The distribution of seismic aftershocks is confined within the region enclosed by the high-resistivity body, following the pattern of the Y-shaped low-resistivity zone. [ABSTRACT FROM AUTHOR]

Coseismic landslides pose a significant threat to the sustainability of both the natural environment and the socioeconomic fabric of society. This escalation in earthquake frequency has driven a growing interest in regional-scale assessment techniques for these landslides. The widely adopted infinite slope model, introduced by Newmark, is commonly utilized to assess coseismic landslide hazards. However, this conventional model falls short of capturing the influence of rock mass structure on slope stability. A novel methodology was previously introduced, considering the roughness of potential slide surfaces on the inner slope, offering a fresh perspective on coseismic landslide hazard mapping. In this paper, the proposed method is recalibrated using new datasets from the 2013 Lushan earthquake. The datasets encompass geological units, peak ground acceleration (PGA), and a high-resolution digital elevation model (DEM), rasterized at a grid spacing of 30 m. They are integrated within an infinite slope model, employing Newmark's permanent deformation analysis. This integration enables the estimation of coseismic displacement in each grid area resulting from the 2013 Lushan earthquake. To validate the model, the simulated displacements are compared with the inventory of landslides triggered by the Lushan earthquake, allowing the derivation of a confidence level function that correlates predicted displacement with the spatial variation of coseismic landslides. Ultimately, a hazard map of coseismic landslides is generated based on the values of the certainty factor. The analysis of the area under the curve is utilized to illustrate the improved effectiveness of the proposed method. Comparative studies with the 2014 Ludian earthquake reveal that the coseismic landslides triggered by the 2013 Lushan earthquake predominantly manifest as shallow rock falls and slides. Brittle coseismic fractures are often associated with reverse seismogenic faults, while complaint coseismic fractures are more prevalent in strike–slip seismogenic faults. The mapping procedure stands as a valuable tool for predicting seismic hazard zones, providing essential insights for decision-making in infrastructure development and post-earthquake construction endeavors. [ABSTRACT FROM AUTHOR]

In this work, the correlations between spatial distributions of landslide point density (LPD) and strong ground motions of the three strong earthquakes are qualitatively investigated. Meanwhile the qualitative relationship between the distribution of LPD and the fault rupture process is also characterized. Three strong events are the Lushan, Wenchuan, and Jiuzhaigou earthquakes. In order to reconstruct the near filed strong ground motions and the fault processes of these earthquakes, the broadband ground simulation method of University of California Santa Barbara (UCSB) and the simplified crustal layer structures are applied. To show the rationality of the UCSB method, the fault slip distributions of the three earthquakes reconstructed by the kinematic rupture generator model in the UCSB method are compared with those by inversed. Furthermore, the validation of the UCSB method for the three earthquakes is also carried according to the validation exercise of the Southern California Earthquake Center (SCEC) Broadband Platform (BBP). Lastly, the fields of peak ground acceleration (PGA) and peak ground velocity (PGV) in three mutually perpendicular directions of the three earthquakes are achieved. Generally, the landslide distribution length of large LPD values along the fault strike is less than the fault strike length. Therefore, the slip modes of earthquake faults affect the distributions of landslides. For the strike slip earthquakes, the distributions of large LPD values relate well to PGA and PGV components of the parallel and normal to the fault strike. For the reverse slip earthquakes, distributions of LPD relate to ground motion components in all directions. Moreover, distributions of landslides in near fields of earthquakes are significantly affected by the focus parameters and fault scales. [ABSTRACT FROM AUTHOR]

On 1 June 2022, a magnitude 6.1 earthquake struck the southern segment of the Longmenshan fault zone on the eastern edge of the Tibetan Plateau, once again causing casualties and economic losses. Understanding the deep-seated dynamic mechanisms that lead to seismic events in the Lushan earthquake area and assessing the potential hazards in seismic gap areas are of significant importance. In this study, we utilized 118 magnetotelluric datasets collected from the Lushan earthquake area and employed three-dimensional electromagnetic inversion with topographic considerations to characterize the deep-seated three-dimensional resistivity structure of the Lushan earthquake area. The results reveal that the Shuangshi–Dachuan fault in the Lushan earthquake area can be divided into two relatively low-resistivity zones: a western zone dipping southeastward and an eastern zone with a steeper slightly northwestern dip. These two zones intersect at a depth of approximately 20 km, forming an extensional pattern resembling a “Y” shape. The epicenters of both the 2013 and 2022 Lushan earthquakes are primarily located in the upper constricted portion of the pocket-like low-resistivity body at depth. The distribution of seismic aftershocks is confined within the region enclosed by the high-resistivity body, following the pattern of the Y-shaped low-resistivity zone.

A precise finite‐fault model including the fault geometry and slip distribution is essential to understand the physics of an earthquake. However, the conventional linear inversion of geodetic data for a finite‐fault model cannot fully resolve the fault geometry. In this study, we developed a Bayesian inversion framework that can comprehensively solve a non‐planar fault geometry, the corresponding fault slip distribution with spatially variable directions, and objective weighting for multiple data types. In the proposed framework, the probability distributions of all the model parameters are sampled using the Monte Carlo method. The developed methodology removes the requirement for manual intervention for the fault geometry and data weighting and can provide an ensemble of plausible model parameters. The performance of the developed method is tested and demonstrated through inversions for synthetic oblique‐slip faulting models. The results show that the constant rake assumption can significantly bias the estimates of fault geometry and data weighting, whereas additional consideration of the variability of slip orientations can allow plausible estimates of a non‐planar fault geometry with objective data weighting. We applied the method to the 2013 Mw 6.5 Lushan earthquake in Sichuan province, China. The result reveals dominant thrust slips with left‐lateral components and a curved fault geometry, with the confidence interval of the dip angles being between 20°–25° and 56°–58°. The proposed method provides useful insights into the scope of imaging a non‐planar fault geometry, and could help to interpret more complex earthquake sources in the future. Plain Language Summary: An earthquake originates from a rapid relative movement between two blocks on both sides of a fault. The earthquake can produce ground deformation, which can be measured by geodetic instruments deployed on the ground. Geophysicists can thus utilize the geodetic measurements to invert the earthquake attributes, including the fault geometry and the associated slips (i.e., the zone and amount of the relative movement between two blocks). Simultaneous estimation of the fault geometry parameters and the slip parameters is a nonlinear problem. The conventional inversion of geodetic data uses a linear adjustment method that cannot fully resolve the fault geometry. In addition, geodetic measurements have different precisions in terms of the types of instruments. We developed a nonlinear inversion based Bayesian inference framework to solve both these problems. The proposed method can correctly interpret an earthquake source with a non‐planar fault geometry. We applied the method to the 2013 Mw 6.5 Lushan earthquake in southwest China and determined a statistical estimate of the fault geometry and slips. The results indicate that the proposed method could help to improve our knowledge of complicated earthquake sources in the future. Key Points: We develop a Bayesian finite‐fault inversion for non‐planar fault geometry and spatially variable slip amplitude and rakeAccounting for variable directions of fault slips allows to better constrain non‐planar fault geometry and tune objective data weightingAccounting for the non‐planar fault geometry, the 2013 Lushan earthquake modeling reveals a dominant thrust slip with sinistral component [ABSTRACT FROM AUTHOR]

At 17:00 (UTC+8) on 1 June 2022, an Ms 6.1 reverse earthquake struck Lushan County, Ya'an City, Sichuan Province. This earthquake event had a focal depth of 10 km and the epicenter was located at 30.37° N and 102.94° E. The purpose of this study is to document a comprehensive coseismic landslide inventory for this event and analyze the distribution pattern and factors controlling the landslides. After careful visual interpretations, this quake event was determined to have in total triggered about 2352 landslides in an area of 3900 km2, including both shallow disrupted landslides and collapses, for which the spatial distribution was statistically related to regional topography, geology, and seismicity. Notably, a vast majority of the landslides were located on the NW plate of the seismogenic fault, and were distributed in the area with a seismic intensity of VII. In addition, coseismic landslides were more likely to appear in areas with high altitude, relief, and large slope. The landslide area density (LAD) increased with an increase in the above factors and is explained by an exponential relationship, indicating that the occurrence of coseismic landslides in this area was more easily affected by topographic factors than seismic factors. Most small-scale landslides were clustered in the ridge area, which shows the seismic amplification effects of mountain slopes. Due to the impact of seismic wave propagation direction, hillslopes facing northeast-east (NE-E) were more prone to collapse than southwest-facing ones. Based on the distribution pattern of the landslides, we suggest that the seismogenic fault of this event was NW dipping. These findings indicate that it is effective to identify the dipping of seismogenic faults using the spatial distribution pattern of coseismic landslides. [ABSTRACT FROM AUTHOR]

Timely response to earthquake characterization can facilitate earthquake emergency rescue and further scientific investigations. On June 1, 2022, MW 5.9 earthquake occurred in the southern area of the Longmenshan fault zone. This event also happened at the south end of the Dayi seismic gap and is the largest earthquake that has occurred in this seismic gap since the 1970 M 6.2 event. The slip-distribution model constrained by the seismic waveforms suggests a thrust-dominated faulting mechanism. The main slip occurs at a depth of ∼14 ​km, and the cumulative energy is released in the first 6 ​s. The variations of Coulomb stress caused by the mainshock show a positive change in the southwest area of the Dayi seismic gap, indicating possible activation of future earthquakes. In addition, we emphasize the importance of rapid estimation of deformation for near-field hazard delineation, especially when interferometric radar fails to image coseismic deformation in a high relief terrain.

In recent years, the Sichuan-Yunnan region has successively occurred the 2008 Wenchuan Ms8. 0 earthquake, the 2013 Lushan Ms7. 0 earthquake, the 2014 Ludian Ms6. 5 earthquake and the 2017 Jiuzhaigou Ms7. 0 earthquake, all of which caused a large number of earthquake landslide disasters. Through statistical analysis, seven factors, namely ground peak acceleration (PGA), seismic intensity, fault distance, stratigraphic lithology, elevation, slope and aspect, were selected from three major factors of earthquake, topography and geology, and the distribution law of landslide induced by these four strong earthquakes was compared and analyzed, and some common features were found. The four earthquakes showed a positive correlation between landslide distribution (number and density) and PGA and magnitude. The more complex geological landforms ( gully development, large slopes) the more landslides. The maximum distance of landslide distribution increased with the increase of earthquake magnitude. In addition, difference characteristics were found. In the near fault area with a maximum impact distance of 0. 2 times, Wenchuan seismic landslides accounted for 76%, while the other three earthquakes accounted for only 27% . Landslides were distributed in relatively weak strata (Quaternary strata, soft strata, etc. ) and had the least distribution of landslides in hard rock areas. In view of the differences, the causes were discussed from the properties of seismic faults, magnitude, stratigraphic lithology, seismic intensity, and fault misalignment direction. [ABSTRACT FROM AUTHOR]

Extremely hard-hit areas face frequent secondary geological hazards and difficulties in vegetation recovery, and subsequent effects have a significant impact on land cover changes. At present, there is a lack of research on the dynamic restoration of, and changes in, the ecological environment before and after an earthquake, and especially a lack of quantitative assessment of the impact of earthquakes on land cover at the microscopic scale of spatial distribution of landscape indices. Taking the Lushan earthquake in Sichuan Province as an example, this paper obtained land cover data from the study area between 2012 and 2020, and analyzes the spatial distribution characteristics and influencing factors of land cover change frequency by using a comprehensive land cover degree index, land cover transfer matrix and landscape ecology index. The results show that the types of cropland, forest, built-up and bare land have changed significantly in the study area. During the earthquake recovery period, the comprehensive land cover index of the study area showed an increasing trend, and land cover has been continuously improved under the effect of artificial measures and natural restoration. After 2013, patch density (PD) and landscape shape index (LSI) values decreased and aggregation index (AI) values increased for the vast majority of landscape land classes, indicating a benign ecological development across the region in the post-earthquake period. The research results are not only helpful to establish scientific ecological environmental management in the earthquake-stricken areas, but also helpful to formulate medium- and long-term ecological environmental monitoring and ecological restoration plans based on land cover change patterns. [ABSTRACT FROM AUTHOR]

In the Longmenshan thrust belt, the Dayi seismic gap, an area with few earthquakes, is located between the ruptures of the 2008 Wenchuan Earthquake and the 2013 Lushan Earthquake, with a length of approximately 40–60 km. To date, however, the extent of the seismic hazard of the Dayi seismic gap and whether this gap is under high stress are still hotly debated. To further evaluate the seismic hazard of the Dayi seismic gap with regard to stress, two boreholes (1,000 and 500 m deep) were arranged to carry out hydraulic fracturing in situ stress measurement on either side of the Shuangshi-Dachuan fault zone. This zone has a high seismic hazard and the capacity to undergo surface rupture Through the analogy of this new data with stability analysis using Byerlee's Law and existing stress measurement data collected before strong earthquakes, the results show that the area surrounding the Shuangshi-Dachuan fault zone in the Dayi seismic gap (Dachuan Town) is in a state of high in situ stress, and has the conditions necessary for friction slip, with the potential hazard of moderate to strong earthquakes. Our results are the first to reveal the in situ stress profile at a depth of 1,000 m in the Dayi seismic gap, and provide new data for comprehensive evaluation of the seismic hazard in this seismic gap, which is of great significance to explore the mechanism of earthquake occurrence and to help mitigate future disaster. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Engineering Geology / Gongcheng Dizhi Xuebao is the property of Journal of Engineering Geology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

To reveal the distribution pattern of aftershocks of the Mw 6.6 Lushan earthquake on April 20, 2013, we analyzed finite-source slip models from seismic waveform inversions and calculated the stress changes on and off the main rupture. In the spatial domain, the fitted coseismic slip–stress relation on subfaults is much closer to the quadratic stress drop model than to the uniform stress model. In the wavenumber domain, the slip and stress change spectrum decay asymptotically as k−3 and k−2, respectively, where k is the wavenumber. And in this domain, we also find that the prediction of a quadratic stress drop model matches data better than a uniform stress drop model. In addition, we studied the effective friction coefficient on the fault. Aftershocks were clustered around a relatively narrow zone that counters the main rupture plane. The narrow zone has a main rupture width with a standard deviation of 2.7 km for M ≥ 3 events. For 12 M ≥ 4.8 aftershocks, approximately 33% of nodal planes were calculated to be located in the zone of positive shear stress changes, while 83% were in the zone of positive normal stress changes (unclamp), suggesting a high effective friction coefficient μ ′ ≥ 0.8 on the main fault. Combined with the investigation in aftershocks triggered by blind thrust events at Whittier Narrows (USA), Zemmouri (Algeria), and Gorkha (Nepal), we suggest that the correlation between aftershocks and positive Coulomb stress changes increases with the effective friction coefficient μ ′ , and the effective friction coefficient and normal stress changes play an important role in aftershock triggering of blind thrust events. [ABSTRACT FROM AUTHOR]

YRY-4 borehole strainmeters have been installed in Sichuan Province, China, since 2008, aimed at monitoring the crustal activities associated with earthquakes. In this study, data from six YRY-4 strainmeters at the southwestern endpoint of the Longmenshan fault zone were analysed, to study the relationship of tectonic strain changes with the 2013 Lushan earthquake. We developed a state-space model to remove the strain response due to air pressure, solid tides and the changes in the water level to preferentially isolate non-tectonic disturbances. Strain responses to each influencing factor were estimated using the environmental coefficients computed in the state-space model by an adaptive Kalman filter with measurement noise. The results were consistent with the expected response of the strainmeter systems. The corrected strain considered to originate from underground tectonics provides new insights into the changes in the pre-earthquake strain. Approximate negentropy (ApNe) and ${b}$ value were introduced to quantify the probability distribution of the corrected borehole strain and compared with the local seismic activities. The nearest station and two further stations, almost simultaneously recorded short-term ApNe anomalies six to four months before the earthquake. The anomalous region also had a correspondingly low ${b}$ value. Moreover, the anomaly acceleration rates of each station were dependent on the epicentral distances. Further comparison with the strain of random periods illustrated the significance of the extracted anomalies. Our results indicate that the corrected strain may contain seismogenic information and reflect the accelerated strain accumulation of focal areas before the earthquake.

This study is carried out based on field investigation data obtained over more than 20 days after the 20 April 2013 Lushan Ms7.0 earthquake in Sichuan Province, China. The investigation includes detailed seismic damage data from 3,684 buildings in 428 districts. This research summarizes the seismic characteristics of buildings with different structures in this area and systematically analyzes the cause of damage. Based on this analysis, the seismic vulnerability of various structural forms in different intensity regions is systematically assessed. The damage characteristics are summarized for several types of the structures typical in the region: constrained masonry structures designed following current standards, unengineered constrained masonry structures, unreinforced masonry structures, brick-wood structures, brick-concrete structure, traditional Chinese timber frame structures, reinforced concrete frame structures, tall buildings, and industrial plants. Moreover, the causes of damage to these structures are investigated. Furthermore, through statistical analysis, this study develops a vulnerability matrix for the main building types and compares their vulnerabilities of similar buildings in regions with different earthquake intensities. The research results provide an important reference for earthquake engineers to recognize failure modes in different types of structures (especially those reconstructed after the Wenchuan earthquake, Sichuan Province, China), revise seismic design codes, and formulate future disaster-reduction plans. [ABSTRACT FROM AUTHOR]

Based on the calculation of precise leveling and GPS observation data, the crustal deformation characteristics of the southwest segment of Longmenshan structural belt before the Lushan Mw6.6 earthquake were analyzed. The results indicate: (1) Before the Lushan earthquake, the focus area and the SW section of the Longmenshan structure zone underwent weak crustal deformation and had large-scale crustal stress strengthening. The crustal deformation field was in a locking state, and the far-field area to the NW underwent obvious crustal deformation. This large-scale crustal deformation weakening or even locking phenomenon has a certain indicative significance for the occurrence of future moderately strong earthquakes in the same tectonic background area. (2) The Wenchuan earthquake caused the adjustment of the tectonic stress from the plateau and accelerated the accumulation of stress in the SW part of the Longmenshan structural belt, which contributed to the Lushan earthquake to a certain degree. (3) The seismogenic structure of the Lushan earthquake is not a simple thrust-type structure, but more likely to be an immature and complex blind thrust fault pattern that developed during the expansion and growth period of the multiple thrust nappe structural system. The seismogenic mechanism has reference value for the prediction of moderately strong earthquakes and scientific research in the periphery of the continental plateau. [ABSTRACT FROM AUTHOR]

Copyright of Mountain Research (10082786) is the property of Mountain Research Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

With the increasing frequency of all kinds of natural disasters, strengthening the resilience and disaster prevention capacity of communities, and improving residents' preparedness for disasters, have gradually become effective means of dealing with disaster risks and improving residents' well-being. However, few studies have explored the correlation between community resilience and disaster preparedness. This study uses survey data from 327 households in four districts and counties affected by the Wenchuan earthquake and the Lushan County, Sichuan earthquake in Sichuan Province, China. The study deeply analyzed the characteristics of community resilience and residents' disaster preparedness. We constructed a Tobit regression model to explore the correlations between community resilience and residents' disaster preparedness. The results show that (1) the community resilience and disaster prevention capability reached the general level of disaster risk reduction paradigm, and the overall disaster preparedness of residents was moderate. (2) The higher the score of community connection care, the better the residents' knowledge and skills preparation and overall disaster preparedness. The higher the score of community resource endowment, the weaker the residents' emergency preparedness. The higher the score of community change potential, the stronger the residents' emergency preparedness. The higher the score of community disaster management, the stronger the residents' emergency preparedness, knowledge and skills preparation, and overall preparedness. The higher the community information communication score, the weaker the knowledge and skills preparation of residents. This study deepens the understanding of the relationship between community resilience and residents' disaster preparedness. Furthermore, it provides information for the establishment of resilient disaster prevention systems in communities threatened by disasters and for the formulation of policies to improve residents' ability to avoid disasters. [ABSTRACT FROM AUTHOR]

Extremely hard-hit areas face frequent secondary geological hazards and difficulties in vegetation recovery, and subsequent effects have a significant impact on land cover changes. At present, there is a lack of research on the dynamic restoration of, and changes in, the ecological environment before and after an earthquake, and especially a lack of quantitative assessment of the impact of earthquakes on land cover at the microscopic scale of spatial distribution of landscape indices. Taking the Lushan earthquake in Sichuan Province as an example, this paper obtained land cover data from the study area between 2012 and 2020, and analyzes the spatial distribution characteristics and influencing factors of land cover change frequency by using a comprehensive land cover degree index, land cover transfer matrix and landscape ecology index. The results show that the types of cropland, forest, built-up and bare land have changed significantly in the study area. During the earthquake recovery period, the comprehensive land cover index of the study area showed an increasing trend, and land cover has been continuously improved under the effect of artificial measures and natural restoration. After 2013, patch density (PD) and landscape shape index (LSI) values decreased and aggregation index (AI) values increased for the vast majority of landscape land classes, indicating a benign ecological development across the region in the post-earthquake period. The research results are not only helpful to establish scientific ecological environmental management in the earthquake-stricken areas, but also helpful to formulate medium- and long-term ecological environmental monitoring and ecological restoration plans based on land cover change patterns.

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]

Debris flows often occur in the mountainous watersheds of earthquake-affected areas, and in the Lushan earthquake area of southwestern China, they have become a significant hazard. In this study, the influencing factors and spatial distribution of debris flows were analyzed through a review of their occurrence history. Debris flows are mainly distributed in the northwestern part of the study area, which hosts the greatest density of active faults. The debris flows are generally formed by the 'progressive bulking' effect in channels, and deep incision, lateral erosion, and blockage breaking are common processes that amplify the magnitude of such debris flows. Rainfall thresholds for different types of debris flow were proposed to explain the spatial differences between debris-flow regions, and the temporal variations of those thresholds highlighted how the rainfall conditions required for the occurrence of debris flows have changed. Natural vegetation recovery, reduction in the availability of solid material, and artificial debris-flow control projects play important roles in raising the threshold of the rainfall conditions required for triggering debris flows. [ABSTRACT FROM AUTHOR]

This study performed a comparative analysis of changes in the operating status of initial surviving disaster‐stricken businesses and non‐disaster‐stricken businesses in Lushan County, China, after a devastating earthquake on 20 April 2013. It used a logistic regression model to explore the key factors associated with 'post‐disaster continued business operation' in the long term. Field data were collected from 1,078 businesses and questionnaire data from 263 small businesses between 2013 and 2017. The results indicate that a higher proportion of initial surviving disaster‐stricken businesses than non‐disaster‐stricken businesses managed to remain operational in each observation period. The continued operation of disaster‐stricken businesses after the earthquake was positively associated with the owner's age, previous disaster experience, pre‐disaster financial conditions, closure duration, and borrowing money from family or friends. A negative association was found with the size of the business. The findings serve as a vital reference for strategies to promote post‐disaster continued business operation. [ABSTRACT FROM AUTHOR]

As a case study of spatial and temporal variations in earthquake stress drops between the 2008 Ms 8.0 Wenchuan and 2013 Ms 7.0 Lushan earthquakes, we computed 1828 stress‐drop values for earthquakes with magnitudes 1.7 ≤ ML ≤ 5.0 during an eight‐year time span before and after major earthquakes. We divide the study area into three subregions (the southern segment of the Longmen Shan fault zone; the southwestern junction of the Longmen Shan and Sichuan Basin; and the southwestern margin of the Sichuan Basin) and calculate individual event stress drops in each. The results show that regions of alternating high and low stress drop are found on either side of the southwestern segment of the Longmen Shan fault zone. During the two‐year period after the 2008 Ms 8.0 Wenchuan earthquake, the stress state of the southern Longmen Shan fault shows no significant change. A marked increase in stress level appears about 18 months before the 2013 Ms 7.0 Lushan earthquake near the Lushan hypocenter zone. Two months after the Ms 7.0 event, the stress drops suddenly attenuate, with significantly less seismic energy release per event. We find that changes in the patterns of high and low stress drop values are consistent with the process of stress accumulation or transfer from the pre‐mainshock to post‐mainshock periods. The results indicate that major earthquakes are the dominant cause of temporal and spatial evolution in stress levels. Stress drop variations show obvious temporal and spatial patterns that may suggests subtle changes in the character of stress fields on faults and spatial variations related to local intense compression and tectonic effects. [ABSTRACT FROM AUTHOR]

There have been many practical programs suggested for building resilient cities and communities, many of which have been driven by governments to focus on disaster prevention rather than focusing on the needs of the affected population. The rebuilding resilient homeland (RRH) program discussed in this paper was a post-Lushan earthquake reconstruction, NGO-led, people-oriented experimental program. Therefore, the aim of this paper was to determine the methods used by the NGOs to lead the reconstruction program for "building back better" and identify the role that NGOs can play in state–civil society relations. Harnessing information gathered from fieldwork, interviews, and document reviews, this paper offers an in-depth case study of the RRH program, with a specific focus on the "resilience" associated with infrastructure, capability, mechanisms, and culture, and the "homeland" associated with safe homes, safe communities, safe schools, and a safe future. The program review revealed useful references for the future development of resilient cities and communities, with people-oriented strategies, community involvement and multi-stakeholder collaborations being the three most salient features. This experimental program also revealed that NGOs and governments could use the institutional opportunities arising from disasters to develop cooperative programs to "build back better" and further facilitate state–civil society relations. [ABSTRACT FROM AUTHOR]

The 2008 Mw 7.9 Wenchuan and 2013 Mw 6.7 Lushan earthquakes ruptured the central and southern segments of the Longmenshan thrust belt on the eastern Tibetan Plateau, respectively. The ∼M 7 Tianquan earthquake in 1327 is also thought to have occurred on the southern segment with effects spatially overlapping those of the Lushan earthquake, but the deformation style and seismogenic mechanism of the segment remain poorly understood. Satellite image interpretation, field investigations, and trenching reveal that the Shuangshi-Dachuan fault (SDF) on the southern segment displaces landforms, dips southeast, and is dominated by thrust motion with a left-lateral strike-slip component. The latest and penultimate events along the fault occurred in 1085–1457 CE and 1215 BCE-104 CE, respectively. Some ancient landslides exits along the fault, and one of them formed close to 703 ± 17 yr BP. The ages of the latest event and of the landslide agree well with the occurrence of the Tianquan earthquake, indicating that the earthquake was most likely generated by the SDF. Magnetotelluric imaging and the aftershock belt of the Lushan earthquake show that the Longmen Shan forms a wedge-shaped high-resistivity body protruding eastward. The SDF corresponds well to the east-dipping upper electrical boundary of the wedge-shaped body and is interpreted as a shallow backthrust; the seismogenic fault of the Lushan earthquake corresponds to the west-dipping lower boundary and is interpreted as a blind thrust fault. The left-lateral slip component of the SDF may be a response to the lateral extension of the weak lower crust. • The Shuangshi-Dachuan fault is a shallow backthrust of the Longmenshan thrust belt. • The Shuangshi-Dachuan fault (SDF) hosted the 1327 Tianquan earthquake. • The 2013 Lushan earthquake occurred on a blind thrust fault located under the SDF. • The SDF and the blind thrust fault correspond to the electrical structure boundary. • The electrical structure boundary had a controlling effect on the earthquakes. [ABSTRACT FROM AUTHOR]

Based on finite element method, the extrusion deformation process of ground surface during the Lushan earthquake (April 20, 2013) is investigated in this work. In order to construct the finite element model of Lushan earthquake structure, the geophysical layer model of Lushan area, the frictional characteristic of slip-weaken along the fault surface, and the Coulomb failure criterion are considered. Through the computation and the comparison with achievement on the Lushan focal dynamics, our researches indicate that: (1) The most extrusion deformation of ground surface occurred in the initial phase of earthquake procession, i.e., between the fourth and sixth seconds after the earthquake occurred. (2) Between the first and sixth seconds after the earthquake, the extrusion deformation concentrates on the surface projection of earthquake fault. (3) Between the first and third seconds after the earthquake, the extrusion deformation of ground surface is very tiny. Meanwhile, the extrusion deformation reaches maximum at the sixth second after earthquake. (4) After 6 s of Lushan earthquake, the extrusion deformation spread out of earthquake structure projection. (5) During the earthquake, the maximum of extrusion deformation on ground surface is larger than the final deformation of the post-earthquake, in other words, the ground extrusion deformation will lastly reach a relatively small value after the Lushan earthquake occurred.

The stress drop (Δσ) is a fundamental parameter used to quantify source physics, and its uncertainty is closely related to seismic hazard. To reveal the relationship between Δσ uncertainty and resultant ground-motion variability, ground motions produced by the 2013 Mw6.6 Lushan earthquake, characterized by various Δσ values, are simulated using the stochastic empirical Green's function method. First, the variability in spectral amplitudes of simulated ground motions arising from the stochastic rupture process is investigated. Generally, it increases from ~ 0.05 to ~ 0.14 as the period increases up to 2.0 s, irrespective of the Δσ value used. The ground-motion variability due to Δσ uncertainty is then explored. The synthetic spectral amplitude is found to be linearly proportional to Δσb, thus the standard deviation of Δσ (log10 unit) is equal to the standard deviation of the spectral amplitude (log10 unit) multiplied by a factor b. The regressed b values are strongly dependent on the period and generally in the range of 0.7 to 0.6 up to the period of 2.0 s. These results explain how much of the ground-motion variability is caused purely by Δσ uncertainty. Moreover, the standard deviation of the spectral amplitudes is calculated directly from simulations based on random Δσ values following a lognormal distribution. The findings further verify the reliability of the relationship between Δσ uncertainty and ground-motion variability. Assuming that the interevent standard deviation in a ground-motion prediction model is dominated entirely by Δσ uncertainty and the stochastic rupture process, we estimate the standard deviation of log10Δσ (~ 0.2–0.3) for broad regions using various models. [ABSTRACT FROM AUTHOR]

As for the ill-posed coefficient matrix in the process of co-seismic slip distribution inversion, a two-step solution method is proposed, and the Laplace second-order smoothing matrix is used for smooth- ing constraint in this paper. This method not only solves the ill-posed problem of the coefficient matrix, but also suppresses the large gradient variation between adjacent fault patches. During the inversion process of two-step solution method, the L curve method is used to determine the regularization parameters. In this paper, systematic simulation experiments are carried out and the Lushan earthquake is used as an actual earthquake case. The maximum slip inversion results of simulation experiments show that the inversion result of two-step solution method has been improved between 3.34% and 19% than that of one-step solu-tion method in accuracy. The root mean square error inversion result of two -step method is less between 3.3% and 13.3% than that of one - step solution method. The inversion results of the Lushan earthquake show that it is feasible to use the two-step solution for slip distribution inversion. [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]

• The Lushan earthquake occurred at the boundary zone between the high- and low-resistivity bodies. • The crustal structure of the southern Longmen Shan thrust belt matches the multiunit combination seismogenic model. • The seismogenic potential of the southern segment of Longmen Shan is weaker than that of the central segment. Since the Ms 7.0 earthquake occurred in Lushan on April 20, 2013, five years after the Wenchuan Ms 8.0 earthquake, the seismogenic potential of southern Longmen Shan has been a considerable concern. Comparative studies of active faults and deep structures of the Lushan and Wenchuan earthquakes are important to evaluate Longmen Shan potential. Terrace measurements, geophysical surveys and borehole drilling reveal that late Quaternary fault activity in the southern segment of the Longmen Shan thrust belt is weaker than that along the central segment. Magnetotelluric data across the southern segment of the Longmen Shan thrust belt show that the central fault and the front-range fault are the electrical boundaries of the crust and that the Longmen Shan thrust belt is a high-resistivity body. The Lushan earthquake occurred at the boundary zone between the high- and low-resistivity bodies, and the crustal structure of the southern Longmen Shan thrust belt matches the multiunit combination seismogenic model, indicating a potential large earthquake in Longmen Shan. Compared to conditions along the central segment, the low-resistivity layer of the upper and lower crust on the western side of the Songpan-Ganzi block develops along the Xianshuihe fault, which may reduce the strain accumulated from the Songpan-Ganzi block to the southern Longmen Shan thrust belt. This interpretation suggests that the main crustal shortening is accommodated by foreland thin fold structures, whereas the structural deformation accommodated by the thrust belt accounts for only a small proportion; thus, the seismogenic potential of southern Longmen Shan is weaker than that of the central segment. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The viscosities of the middle-lower crust of the Longmenshan Thrust Belt (LTB), China, are studied. • Rheological properties are not the main controlling factor on fault activity of the LTB. • The lower fault activity along the southern LTB may be due to a greater number of structures. Abstract Seven continuous GPS stations are located on the hanging wall of the Longmenshan Thrust Belt, and post-seismic deformation data of the 2013 Lushan earthquake have been recorded for nearly four years following the earthquake. We transform the data from a global reference frame to the South China Block reference frame, and then, the secular motion and post-seismic deformation of the Wenchuan earthquake are excluded using an exponential fit model. Based on our results, the viscosities of the low velocity zone at a depth of ∼25 km and of the middle and lower crust around the Longmenshan Thrust Belt are obtained as 2.75 × 10 17 P a · s and 2.56 × 10 18 P a · s , respectively. The post-seismic rebound, which was observed near the Lushan epicenter, may represent the occurrence of overslip during the earthquake. The more complex structural style may have produced weaker fault activity along the southern segment of the Longmenshan Thrust Belt than along its middle and northern segments. [ABSTRACT FROM AUTHOR]

On April 20th 2013, Ms 7.0 earthquake occurred on the southern section of the Longmen Shan fault, in Sichuan Province. In this research, the three-dimensional coseismic displacement field that GPS data from 33 continuous stations are used to invert for fault geometry parameters and the slip distribution. The MPSO (multiple peak particle swarm optimization) algorithm has been successfully applied to invert for the fault model parameters.Compared with the commonly used algorithm, such as genetic algorithm, simulated annealing and the overall minimum norm optimization algorithm, MPSO algorithm has the advantages of less control parameters, high global convergence efficiency, and is very suitable for nonlinear inversion of fault parameters. The result indicates that the seismogenic fault is a thrust with a strike of 206.47°, a dip of 44.11°, and length of 21.94 km. The minimum and maximum depth is 7.66 km and 17.84 km, respectively. The fracture surface was determined as listric surface by analysis. In order to obtain the detailed slip distribution, the listric surface model is set with the default dip angle varying from 50° on the top boundary of the surface to 21° on the bottom boundary. Our inversion result shows that the rupture surface has two slip peaks at different depths. The maximum slip is 0.68 m at the depth of 13 km. The inverted geodetic moment is 1.47×1019 N·m and the moment magnitude Mw is 6.74, which is consistent with the result of seismology. [ABSTRACT FROM AUTHOR]

The April 20, 2013 Mw6.6 earthquake of Lushan County, Sichuan Province, China, has triggered 4540 landslides (> 1000 m2). Exploring a more effective method to assess landslide hazard in the affected area of this event is of great significance for disaster prevention and mitigation. By applying the Newmark model and two statistical analysis models (logic regression and support vector machine, LR and SVM), this study addressed this issue. In the Newmark model, we used the landslide point density, the average gradient (mean slope) and the mean peak ground acceleration to group the lithology and created a critical acceleration (ac) map. The Newmark displacements and the probability of the slope instability are mapped by combining the ac map and PGA map. In the statistical analysis models of LR and SVM, 7040 samples (4540 landslide sites and 2500 random non-landslide sites) were randomly divided into the training set (5000 samples) and validation set (2040 samples). Based on the relationship between landslide distribution and influence factors, we selected the critical acceleration (ac) value, topographic relief, PGA, and distance to rivers as the independent variables for LR and SVM. Finally, the ROC curves for three landslide hazard models were drawn and the AUC values were calculated. The landslide hazard maps produced by LR are similar to those by applying SVM. The AUC values indicate that these two models combined with ac data perform better than the simplified Newmark model. In this study, a new method of integrating statistical analysis models (LR and SVM) with critical acceleration (ac) for earthquake landslide hazard assessment is presented, which can be used to carry out seismic landslide hazard assessment more effectively than the simplified Newmark model. [ABSTRACT FROM AUTHOR]

The seismic behavior of a school gymnasium, whose steel grid roof was heavily damaged during the Mw6.6 Lushan earthquake in 2013, is simulated through nonlinear dynamic analysis. The simulated damage is compared with field observations to validate the numerical model, based on which a parametric study was performed to provide insight into the failure process and damage patterns of steel grids. The results suggest that the grid damage is strongly related to roof-substructure interactions. These include not only the substructure's amplification of the vibration, but the uncoordinated displacement of the substructure's columns which support the grid also play an equally important role. In particular, the latter effect may significantly alter the internal force distribution in the steel grid and lead to unexpected buckling of members that are proportioned as tension-only members. While such interactions are generally not accounted for in the design practice for grid structures in China, similar seismic damage may be expected for other existing grid roofs in future earthquakes. As is also demonstrated in this study, seismic isolation of the roof is a promising solution to protect grid roof structures by mitigating the detrimental effects of roof-substructure interactions. [ABSTRACT FROM AUTHOR]

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Abstract Usually, GPS observation provides direct evidence to estimate coseismic displacement. However, GPS stations are scattered, sparse and cannot provide a detailed distribution of coseismic displacement. Strong ground motion records share the same disadvantages as GPS in estimating coseismic displacement. Estimations from InSAR data can provide displacement distributions; however, the resolution of such methods is limited by the analysis techniques. The paper focuses on estimating the coseismic displacement of the M S7.0 Lushan earthquake on April 20, 2013 using a simulation of the wave field based on the elastic wave equation instead of a quasi-static equation. First, the media and source models were constructed by comparing the simulated velocity and the record velocity of the ground motion. Then simulated static displacements were compared with GPS records. Their agreement validates our results. Careful analysis of the distribution of simulated coseismic displacements near the fault reveals more details of the ground motion. For example, an uplift appears on the hanging wall of the fault, rotation is associated with the horizontal displacement, the fault strike and earthquake epicenter provide the main control on motion near the faults, and the motion on the hanging wall is stronger than that on the footwall. These results reveal additional characteristics of the ground motion of the Lushan earthquake.