Airblast evolution initiated by Wangjiayan landslides in the M_(s)8.0 Wenchuan earthquake and its destructive capacity analysis

Airblasts,as one common phenomenon accompanied by rapid movements of landslides or rock/snow avalanches,commonly result in catastrophic damages and are attracting more and more scientific attention.To quantitatively analyze the intensity of airblast initiated by landslides,the Wangjiayan landslide,occurred in the Wenchuan earthquake,is selected here with the landslide propagation and airblast evolution being studied using FLUENT by introducing the Voellmy rheological law.The results reveal that:(1)For the Wangjiayan landslide,its whole travelling duration is only 12 s with its maximum velocity reaching 36 m/s at t=10 s;(2)corresponding to the landslide propagation,the maximum velocity,28 m/s,of the airblast initiated by the landslide also appears at t=10 s with its maximum pressure reaching594.8 Pa,which is equivalent to violent storm;(3)under the attack of airblast,the load suffered by buildings in the airblast zone increases to 1300 Pa at t=9.4 s and sharply decreased to-7000 Pa as the rapid decrease of the velocity of the sliding mass at t=10 s,which is seriously unfavorable for buildings and might be the key reason for the destructive collapse of buildings in the airblast zone of the Wangjiayan landslide.

Analysis of debris flow control effect and hazard assessment in Xinqiao Gully,Wenchuan M_(s)8.0 earthquake area based on numerical simulation

Xinqiao Gully is located in the area of the 2008 Wenchuan M_(s)8.0 earthquake in Sichuan province,China.Based on the investigation of the 2023"6-26"Xinqiao Gully debris flow event,this study assessed the effectiveness of the debris flow control project and evaluated the debris flow hazards.Through field investigation and numerical simulation methods,the indicators of flow intensity reduction rate and storage capacity fullness were proposed to quantify the effectiveness of the engineering measures in the debris flow event.The simulation results show that the debris flow control project reduced the flow intensity by41.05%to 64.61%.The storage capacity of the dam decreases gradually from upstream to the mouth of the gully,thus effectively intercepting and controlling the debris flow.By evaluating the debris flow of different recurrence intervals,further measures are recommended for managing debris flow events.

Identifying drivers of urban landuse changes in the Wenchuan earthquake- affected area by using night-time light data

To learn the process of urban land evolution before and after an earthquake is vital to formulate the urban reconstruction control policies and recovery measures in the earthquake-stricken areas.However,spatiotemporal evolution and its driving factors of urban land in earthquake-prone areas remains limited due to the scarcity of ground observation data.This research,leveraging night-time light remote sensing imagery and land cover data,conducted a comprehensive analysis of the long-term evolution characteristics of urban land in earthquake-prone areas.It introduced methodologies for assessing the socio-economic impact and the primary natural environmental factors driving urban land evolution in these regions.To validate the proposed methods,the 2008 Wenchuan earthquake-affected area in China was selected as a representative study area.The results indicated that the average Digital Number(DN)values in socio-economically impacted areas showed a trend of rising,falling,and then rising again after the earthquake.DN values in three types of damaged areas including Type Ⅱ,Type Ⅲ,and Type Ⅳ exceeded pre-earthquake levels.The analysis of determinative factors influencing urban land evolution revealed that slope and elevation were key elements in controlling urban land expansion before the earthquake,whereas factors such as slope,elevation,lithology,and faults had a stronger influence on urban land expansion after the earthquake.It can be seen that,in view of the differences in the natural conditions of regions for post-disaster reconstruction,the local government need to actively adjust and adapt to urban spatial planning,so as to leverage the scale effect of large-scale inputs of funds,facilities,human resources and other factors after the disaster,thus enhancing resilience and recovery efficiency in response to disaster impacts.

A comparative study of the main factors controlling geohazards induced by 10 strong earthquakes in Western China since the Wenchuan earthquake in 2008

Determining the main controlling factors of earthquake-triggered geohazards is a prerequisite for studying earthquake geohazards and post-disaster emergency response.By studying these factors,the geomorphic and geological factors controlling the nature,condition,and distribution of earthquake-induced geohazards can be analyzed.Such insights facilitate earthquake disaster prediction and emergency response planning.The authors combined field investigations and spatial data analysis to examine geohazards induced by seismic events,examining ten earthquakes including the Wenchuan,Yushu,Lushan events,to elucidate the main control factors of seismic geohazard.The authors observed that seismic geohazard occurrence is usually affected by many factors,among which active nature of the seismogenic fault,seismic peak ground acceleration(PGA),topographic slope and geomorphic height differences,and distance from the fault zone and river system are the most important.Compared with strike-slip earthquakes,thrust earthquakes induce more high-altitude and high-speed remote landslides,which can cause great harm.Slopes of 0°–40°are prone to secondary seismic geohazards,which are mainly concentrated 0–6 km from the river system.Secondary geohazards are not only related to seismogenic fault but also influenced by the associated faults in the earthquake area.The maximum seismic PGA and secondary seismic geohazard number are positively correlated,and the horizontal and vertical ground motions play leading and promoting roles in secondary geohazard formation,respectively.Through the research,the spatial distribution of seismic geohazards is predicted,providing a basis for the formulation of emergency response plans following disasters.

Transient postseismic slip and aftershock triggering:A case study of the 2008 M_W7.9 Wenchuan Earthquake,China

In this study,we investigate how a stress variation generated by a fault that experiences transient postseismic slip(TPS)affects the rate of aftershocks.First,we show that the postseismic slip from Rubin-Ampuero model is a TPS that can occur on the main fault with a velocity-weakening frictional motion,that the resultant slip function is similar to the generalized Jeffreys-Lomnitz creep law,and that the TPS can be explained by a continuous creep process undergoing reloading.Second,we obtain an approximate solution based on the Helmstetter-Shaw seismicity model relating the rate of aftershocks to such TPS.For the Wenchuan sequence,we perform a numerical fitting of the cumulative number of aftershocks using the Modified Omori Law(MOL),the Dieterich model,and the specific TPS model.The fitting curves indicate that the data can be better explained by the TPS model with a B/A ratio of approximately 1.12,where A and B are the parameters in the rate-and state-dependent friction law respectively.Moreover,the p and c that appear in the MOL can be interpreted by the B/A and the critical slip distance,respectively.Because the B/A ratio in the current model is always larger than 1,the model could become a possible candidate to explain aftershock rate commonly decay as a power law with a p-value larger than 1.Finally,the influence of the background seismicity rate r on parameters is studied;the results show that except for the apparent aftershock duration,other parameters are insensitive to r.

Characteristics of the coseismic geomagnetic disturbances recorded during the 2008 M_w 7.9 Wenchuan Earthquake and two unexplained problems

Twenty-seven FHDZ-M15 combined geomagnetic observation systems(each of which is equipped with a fluxgate magnetometer and a proton magnetometer)had been installed in the China geomagnetic network before the 2008 Wenchuan earthquake,during which coseismic disturbances were recorded by 26 fluxgate magnetometer observatories.The geomagnetic disturbances have similar spatial and temporal patterns to seismic waves,except for various delays.Six proton magnetometer observatories recorded coseismic disturbances with very small amplitudes.In addition,fluxgate magnetometers registered largeamplitude disturbances that are likely to have included responses to seismic waves.However,two problems remain unresolved.First,why do these geomagnetic disturbances always arrive later than P waves?Second,why do the geomagnetic disturbances have spatial and temporal directivity similar to the main rupture direction of the earthquake?Solving these two problems may be crucial to find the mechanism responsible for generating these geomagnetic anomalies.

Surface Rupture and Co-seismic Displacement Produced by the Ms 8.0 Wenchuan Earthquake of May ^(12)th,2008,Sichuan,China:Eastwards Growth of the Qinghai-Tibet Plateau

女士 8 的地震给 Wenchuan 以县，西方的四川，中国，在 2008 年 5 月 12 日并且导致了长表面破裂(> 300 km ) 。关于表面破裂的第一手的观察在 Yingxiu， Beichuan 和 Qingchuan 的最糟点击的区域由地震生产了，查明地震的原因的结构在 Longmenshan 构造的带的中央差错地区。沿着 Yingxiu-Beichuan 破裂地区活动范围 2.5-4 m 的单个差错的平均 co 地震的垂直排水量和越过中央、正面的 Longmenshan 差错的累积垂直排水量系上带子是大约 56 m。表面破裂力量从 Beichuan 的北方被归结为 Qingchuan 县和表演 23 m 右罢工滑倒部件。Wenchuan 指责戳的地震是在印度、欧亚的大陆的连续集中的行动下面的西藏的高原的东方生长的表明。

Co-seismic Faults and Geological Hazards and Incidence of Active Fault of Wenchuan Ms 8.0 Earthquake,Sichuan,China

There are two co-seismic faults which developed when the Wenchuan earthquake happened. One occurred along the active fault zone in the central Longmen Mts.and the other in the front of Longmen Mts.The length of which is more than 270 km and about 80 km respectively.The co-seismic fault shows a reverse flexure belt with strike of N45°-60°E in the ground,which caused uplift at its northwest side and subsidence at the southeast.The fault face dips to the northwest with a dip angle ranging from 50°to 60°.The vertical offset of the co-seismic fault ranges 2.5-3.0 m along the Yingxiu-Beichuan co-seismic fault,and 1.5-1.1 m along the Doujiangyan-Hanwang fault.Movement of the coseismic fault presents obvious segmented features along the active fault zone in central Longmen Mts. For instance,in the section from Yingxiu to Leigu town,thrust without evident slip occurred;while from Beichuan to Qingchuan,thrust and dextral strike-slip take place.Main movement along the front Longmen Mts.shows thrust without slip and segmented features.The area of earthquake intensity more thanⅨdegree and the distribution of secondary geological hazards occurred along the hanging wall of co-seismic faults,and were consistent with the area of aftershock,and its width is less than 40km from co-seismic faults in the hanging wall.The secondary geological hazards,collapses,landslides, debris flows et al.,concentrated in the hanging wall of co-seismic fault within 0-20 km from co-seismic fault.

Wenchuan Ms8.0 earthquake coseismic slip distribution inversion

By using GPS and gravity data before and after the Wenchuan Ms8.0 earthquake and combining data from geological surveys and geophysical inversion studies, an initial coseismic fault model is constructed. The dip angle changes of the fault slip distribution on the fault plane are inversed, and the inversion results show that the shape of the fault resembles a double-shovel. The Yingxiue Beichuan Fault is approximately 330 km long, the surface fault dip angle is 65.1, which gradually reduces with increasing depth to 0 at the detachment layer at a depth of 19.62 km. The Guanxiane Jiangyou Fault is approximately90 km long, and its dip angle at the surface is 55.3, which gradually reduces with increasing depth; the fault joins the Yingxiue Beichuan Fault at 13.75 km. Coseismic slip mainly occurs above a depth of 19 km. There are five concentrated rupture areas, Yingxiu,Wenchuan, Hanwang, Beichuan, and Pingwu, which are consistent with geological survey results and analyses of the aftershock distribution. The rupture mainly has a thrust component with a small dextral strikeeslip component. The maximum slip was more than10 m, which occurred near Beichuan and Hanwang. The seismic moment is 7.84 1020 Nm(Mw7.9), which is consistent with the seismological results.

Mercury indicating inflow zones and ruptures along the Wenchuan Ms 8.0 earthquake fault

During the Wenchuan Fault Scientific Drilling Project,we determined the values of total mercury(HgT)and gaseous elemental mercury(GEM) from drilled cores and drilling mud,respectively.Geochemical analysis shows HgT values ranging from 0.24 to 6.45 ng/g for the Penguan complex and from 2.90 to 137.54 ng/g for T3 sediment.The average levels of HgT for the Penguan complex and T3 sediments are 1.81 ± 0.26 ng/g and23.96 ± 4.80 ng/g,respectively.Major anomalous peaks of HgT appear at depth of 614,731,993 and 1,107 m,which correspond to the long-term high seismic activity during crustal deformation in response to tectonic stresses.Gaseous elemental mercury dissolved in drilling mud was also analyzed.We found fluid inflow zones with high GEM at depths of 590-750 m,suggesting that fluid-filled ruptures exist in the LMS fault zone.It indicates that mercury provides geochemical evidence for inflow zones and ruptures/fault zones in the Wenchuan Ms 8.0 earthquake fault.

Temporal variation of gravity field before and after Wenchuan Ms8.0 earthquake

Absolute and relative gravity data during 1998 to 2008 were used to study gravity field and temporal variation in the North-South seismic-belt region,and their correlation with seismic activities before and after Wenchuan Ms8.0 earthquake.The temporal variation of gravity field shows that the portentous information of the gravity field reflects the development and occurrence of earthquake more clearly.The variations of gravity field are inhomogeneous in the space-time distribution,and are associated with the development and occurrence of the Wenchuan Ms8.0 earthquake,also closely connected with active fault tectonics.

Ground Surface Ruptures and Near-Fault,Large-Scale Displacements Caused by the Wenchuan Ms8.0 Earthquake Derived from Pixel Offset Tracking on Synthetic Aperture Radar Images

The 12 May 2008 Wenchuan Ms8.0 earthquake produced surface displacements along the causative fault,the Yingxiu-Beichuan Fault,which are up to several meters near the fault.Because of the large gradient,satellite synthetic aperture radar(SAR) interferometric data are strongly incoherent;the usual SAR interferometry method does not allow such displacements to be measured.In the present study,we employed another approach,the technique based on pixel offset tracking,to solve this problem.The used image data of six tracks are from the Advanced Land Observing Satellite,Phased Array type L-band Synthetic Aperture Radar(ALOS/PALSAR) dataset of Japan.The results show that the entire surface rupture belt is 238 km long,extending almost linearly in a direction of 42° north-east.It is offset left laterally by a north-west-striking fault at Xiaoyudong,and turns at Gaochuan,where the rupture belt shifts toward the south by 5 km,largely keeping the original trend.In terms of the features of the rupture traces,the rupture belt can be divided into five sections and three types.Among them,the Beichuan-Chaping and Hongkou-Yingxiu sections are relatively complex,with large widths and variable traces along the trend.The Pingtong-Nanba and Qingping-Jingtang sections appear uniform,characterized by straight traces and small widths.West of Yingxiu,the rupture traces are not clear.North of the rupture belt,surface displacements are 2.95 m on average,mostly 2-3.5 m,with 7-9 m the maximum near Beichuan.South of the rupture belt,the average displacement is 1.75 m,dominated by 1-2 m,with 3-4 m at a few sites.In the north,the displacements in the radar line of sight are of subsidence,and in the south,they are uplifted,in accordance with a right-slip motion that moves the northern wall of the fault to the east,and the southern wall to the west,respectively.Along the Guanxian-Jiangyou Fault,there is a uplift zone in the radar line of sight,which is 66 km long,1.5-6 km wide,and has vertical displacements of approximately 2 m,but no observable rupture traces.

Preparatory mechanism of Ms8.0 Wenchuan earthquake evidenced by crust-deformation data

Some crustal-deformation data related to the Ms8.0 Wenchuan in 2008,was described and a model that is capable of explaining the observed deformation features is presented.The data include:pre-earthquake uplift in an area south of the epicenter obtained by repeated-leveling measurements;pre-earthquake horizontal deformation by GPS observation during two periods in Sichuan-Yunnan area;vertical deformation along a short cross-fault leveling line in the epicenter area;and co-seismic near-field vertical and horizontal crustal-movement data by GPS.The model is basically "elastic-rebound",but involves a zone between two local faults that was squeezed out at the time of earthquake.

Surface rupture and hazard characteristics of the Wenchuan Ms 8.0 earthquake, Sichuan, China

Longmen Shan is located the special joint be-tween Tibetan Plateau inland in the west and Yangtze craton in the east. Consisting of a se-ries of parallel imbricated thrust, it develops, from the west to the east, the Maoxian- Wenchuan, Beichuan-Yingxiu and Pengxian- ﹡This research was supported by China National Natural Science Foundation grant 40841010, 40972083 and China National Science and Technology supporting Plan Foundation grant 2006BAC13B02-07, 2006BAC13B01-604. Guanxian faults. The Wenchuan earthquake is a thrust with strike-slip type, and thre surface ruptures are located on the Beichuan-Yingxiu fault zone and Pengxian-Guanxian fault zone. The surface rupture on the Beichuan-Yingxiu fault shows the thrust and dextral slip charac-teristic. The maximum vertical displacement of the surface rupture is about 10.3 m and the maxi-mum right-lateral displacement is about 5.85m. Though the vertical displacements and the hori-zontal displacements in the different segments have certain differences, as a whole, the ratio of the vertical displacement and the horizontal dis-placement is close to 1:1. The surface rupture on the Pengxian-Guanxian fault shows thrust and dextral characteristic. The rates of vertical dis-placements and the horizontal displacements ones on the most other segments are between 1:3 and 1:2. So the Beichuan- Yingxiu fault is a dextral-slip and thrust fault and the average ver-tical displacement is equal to the average hori-zontal displacement, while the Pengxian- Guan xian fault is thrust fault with a little dextral-slip component. The total intensity area above Ⅵ de-gree of the Wenchuan earthquake is about 333000 km2. The high earthquake intensity line stretches to N40-50°E along Longmen Shan tectonic belt. The rate of the long axis and the minor is betw- een 8:1 and 10:1. Three Ⅺ intensity regions are isolated in distribution. It presents a multipoint instantaneous characteristic of the rupture.

Surface Rupture and Hazard of Wenchuan Ms 8.0 Earthquake, Sichuan, China

Longmen Shan is located the special joint between the Qinghai-Tibetan Plateau in the west and the Yangtze craton in the east. Consisting of a series of parallel imbricated thrust, it develops, from the west to the east, the Maoxian-Wenchuan, Yingxiu-Beichuan and Pengxian-Guanxian faults. Wenchuan Ms 8.0 earthquake is a thrust with strike-slip type, and surface ruptures are located in Yingxiu-Beichuan fault zone and Peng- xian-Guanxian fault zone. Based on the geological background, tectonic setting, the active tectonics of Long- men Shan and surface ruptures of the Wenchuan earthquake, a dynamical model to illustrate possible links between surface processes and upward extrusion of lower crustal flow channel at the eastern margin of the Tibetan plateau have been studied, and the results is the material in lower crust in the Longmen Shan moving as nearly-vertical extrusion and uplift, resulting in the surface rate of tectonic movement differing according to depth rate as well as the occurrence of large shallow Wenchuan earthquake.

Analysis of the Wenchuan Ms8.0 Earthquake's Co-seismic Stress and Displacement Change by Using the Finite Element Method

The variation of in situ stress before and after earthquakes is an issue studied by geologists. In this paper, on the basis of the fault slip dislocation model of Wenchuan Ms8.0 earthquake, the changes of co-seismic displacement and the distribution functions of stress tensor around the Longmen Shan fault zone are calculated. The results show that the co-seismic maximum surface displacement is 4.9 m in the horizontal direction and 6.5 m in the vertical direction, which is almost consistent with the on-site survey and GPS observations. The co-seismic maximum horizontal stress in the hanging wall and footwall decreased sharply as the distance from the Longmen Shan fault zone increased. However, the vertical stress and minimum horizontal stress increased in the footwall and in some areas of the hanging wall. The study of the co-seismic displacement and stress was mainly focused on the long and narrow region along the Longmen Shan fault zone, which coincides with the distribution of the earthquake aftershocks. Therefore, the co-seismic stress only affects the aftershocks, and does not affect distant faults and seismic activities. The results are almost consistent with in situ stress measurements at the two sites before and after Wenchuan Ms8.0 earthquake. Along the fault plane, the co-seismic shear stress in the dip direction is larger than that in the strike direction, which indicates that the faulting mechanism of the Longmen Shan fault zone is a dominant thrust with minor strike-slipping. The results can be used as a reference value for future studies of earthquake mechanisms.

Dextral-Slip Thrust Faulting and Seismic Events of the Ms 8.0 Wenchuan Earthquake,Longmenshan Mountains,Eastern Margin of the Tibetan Plateau

Dextral-slip thrust movement of the Songpan-Garzê terrain over the Sichuan block caused the M_s 8.0 Wenchuan earthquake of May 12,2008 and offset the Central Longmenshan Fault(CLF) along a distance of～250 km.Displacement along the CLF changes from Yingxiu to Qingchuan.The total oblique slip of up to 7.6 m in Yingxiu near the epicenter of the earthquake,decreases northeastward to 5.3 m,6.6 m,4.4 m,2.5 m and 1.1 m in Hongkou,Beichuan,Pingtong,Nanba and Qingchuan,respectively.This offset apparently occurred during a sequence of four reported seismic events,EQ1-EQ4,which were identified by seismic inversion of the source mechanism.These events occurred in rapid succession as the fault break propagated northeastward during the earthquake. Variations in the plunge of slickensides along the CLF appear to match these events.The Mw 7.5 EQ1 event occurred during the first 0-10 s along the Yingxiu-Hongkou section of the CLF and is characterized by 1.7 m vertical slip and vertical slickensides.The Mw 8.0 EQ2 event,which occurred during the next 10-42 s along the Yingxiu-Yanziyan section of the CLF,is marked by major dextralslip with minor thrust and slickensides plunging 25°-35°southwestward.The Mw 7.5 EQ3 event occurred during the following 42-60 s and resulted in dextral-slip and slickensides plunging 10°southwestward in Beichuan and plunging 73°southwestward in Hongkou.The Mw 7.7 EQ4 event, which occurred during the final 60-95 s along the Beichuan-Qingchuan section of the CLF,is characterized by nearly equal values of dextral and vertical slips with slickensides plunging 45°-50°southwestward.These seismic events match and evidently controlled the concentrations of landslide dams caused by the Wenchuan earthquake in Longmenshan Mountains.

Characteristics and factors that influenced damage to dams in the M_s 8.0 Wenchuan earthquake

Based on raw data from dams damaged in the Wenchuan earthquake, including many that were severely damaged, characteristics and factors that influenced the damage are discussed in this paper. Findings from this study include: severely damaged dams were densely distributed along the seismologic fault; small dams, especially small earth-rock dams, had the most serious damage that was caused by a variety of factors; the most serious damage was caused by seismic waves; damage was aggregated by aftershocks; and the extent of the damage patterns increased with the seismic intensity. Damage patterns varied in different intensity zones and cracking was the most common type of damage. Most of the dams had a good base with relatively high bearing capacity, and the walls of the earth-rock dams were mostly of clay soil. This type of base and body material mitigated some of the damage to dams. Reservoir maintenance and other factors also have a significant impact on the seismic safety of the dam. Finally, some recommendations to reduce seismic damage to dams are proposed.

Anomalous tremor before 2008 Ms8.0 Wenchuan earthquake: a review

In this paper we give a review of several previously published papers on anomalous tremors observed before the 2008 Ms8.0 Wenchuan earthquake. Based on the observed time and frequency shifts between coastal and inland stations, we discussed some methods to distinguish different kinds of microseisms, and speculated that a pre-earthquake typhoon might have caused a "mainland-originated microseism" which in turn triggered the earthquake.

Simulation of co-seismic gravity change and deformation of Wenchuan Ms8.0 earthquake

co 地震的严肃变化和排水量由 Wenchuan Ms8 引起了的表面。分别地， 0 地震由地球物理， CEA 和 USGS 的研究所根据一半空间脱臼理论和二差错模型 inversed 是计算的。结果显示出那 1 )脱臼由剧降组成滑倒并且权利侧面的罢工滑倒； 2 )co地震的严肃变化证明一个四象限的模式，哪个是极大地由垂直排水量的分发控制了，吗在特别近文件； 3 )严肃变化通常是不到 10 汦潯敤?楷桴？