A study of a flowslide with significant entrainment in loess areas in China

Flowslides are a frequent type of natural disaster in loess areas and may result in the significant loss of properties and/or casualties. The Dagou flowslide is a typical event in a loess area and is accompanied by significant sediment entrainment. To analyze the mechanisms responsible for flowslides and to obtain the parameters for a runout analysis, a field investigation was conducted. Specimens were sampled on site to carry out laboratory tests, including a triaxial test, sieve analysis, and chemical component analysis. The parameters were used in the runout study employing an energy‐based runout model. An analytical entrainment model was adopted to calculate the entrainment after considering physical properties and the mechanism of the entrainment process of the loess. Finally, the entrainment model was incorporated into the runout model to simulate the post‐failure process of this case. Energy dissipation due to the deformation of slices was considered as it was thought to be important for a slide with a significant deformation. The simulation results were compared with the measurements, including runout distance, total volume, erosion depth, deposition height at different sections, and velocities at specific locations. The results indicate that the energy‐based runout model, together with the entrainment model, can capture the kinematic characteristics of the Dagou flowslide. Therefore, it is feasible to use this model to predict the runout characteristics of flowslides in similar areas. Copyright © 2017 John Wiley & Sons, Ltd.     

构建和谐社会中的巨灾风险防范 --我国地震巨灾风险证券化的实证分析

党的十六大首次提出了“和谐社会”的概念,而人与自然的和谐成为这一概念的重要内涵之一.我国作为世界上自然灾害最严重的国家之一,亟需构筑符合我国国情的巨灾风险防范体系.保险风险证券化作为国际保险市场化解巨灾风险的一项重要创新,也正在为我国保险业所关注.为此本文选取了在我国发生频率最高、造成损失最大的自然灾害-地震灾害作为研究对象,对我国地震巨灾债券的构建与定价进行了实证分析,即利用实际的样本数据和有关非寿险精算的有关原理,构建了我国的地震巨灾债券,并同时完成了价格体系的制定.以上研究可以为巨灾风险证券化在我国的推广提供可资参考的方法与依据.     

Morphological response of a barrier island system on a catastrophic event: the AD 1634 North Sea storm

The AD 1634 North Sea storm is one of the most catastrophic storms along the Wadden Sea coast of Denmark. In this study we show how pre‐1634 storm morphology exerted a strong control on the resulting post‐storm coastal morphology. Erosional responses associated with the storm were barrier breaching, dune scarping and shoreface erosion and accretionary responses were washover deposition, shoreface healing and barrier‐island formation. Local sediment sources appeared to have a particularly strong influence on post‐storm coastal evolution and allowed a very rapid formation of a barrier shoal which resulted in several kilometres of coastal progradation. Sediment budgets suggest that formation of the barrier shoal was possible, but the sediment transport rates in the decades after the 1634 storm, must have been two to three times higher than present‐day rates. The study demonstrates that catastrophic storms are capable of moving large amounts of sediments over relatively short time‐periods and can create barrier shoals, whereas moderate storms mostly rework the shoal or barrier and create more local erosion and/or landward migration. Catastrophic storms substantially influence long‐term and large‐scale coastal evolution, and storms may positively contribute to the sediment budget and promote coastal progradation in coastal areas with longshore sediment convergence. Copyright © 2015 John Wiley & Sons, Ltd.     

Study of the flood control scheduling scheme for the Three Gorges Reservoir in a catastrophic flood

The Three Gorges Project is the world's largest water conservancy project. According to the design standards for the 1,000‐year flood, flood diversion areas in the Jingjiang reach of the Yangtze River must be utilized to ensure the safety of the Jingjiang area and the city of Wuhan. However, once these areas are used, the economic and life loss in these areas may be very great. Therefore, it is vital to reduce this loss by developing a scheme that reduces the use of the flood diversion areas through flood regulation by the Three Gorges Reservoir (TGR), under the premise of ensuring the safety of the Three Gorges Dam. For a 1,000‐year flood on the basis of a highly destructive flood in 1954, this paper evaluates scheduling schemes in which flood diversion areas are or are not used. The schemes are simulated based on 2.5‐m resolution reservoir topography and an optimized model of dynamic capacity flood regulation. The simulation results show the following. (a) In accord with the normal flood‐control regulation discharge, the maximum water level above the dam should be not more than 175 m, which ensures the safety of the dam and reservoir area. However, it is necessary to utilize the flood diversion areas within the Jingjiang area, and flood discharge can reach 2.81 billion m³. (b) In the case of relying on the TGR to impound floodwaters independently rather than using the flood diversion areas, the maximum water level above the dam reaches 177.35 m, which is less than the flood check level of 180.4 m to ensure the safety of the Three Gorges Dam. The average increase of the TGR water level in the Chongqing area is not more than 0.11 m, which indicates no significant effect on the upstream reservoir area. Comparing the various scheduling schemes, when the flood diversion areas are not used, it is believed that the TGR can execute safe flood control for a 1,000‐year flood, thereby greatly reducing flood damage.     

Hydrological importance of an unusual hazard in a mountainous basin: flood and landslide

The Bhagirathi River, a proglacial melt water stream of the Gangotri Glacier, is the principal source of the Ganges river system. The upper part of the basin lies in the high altitude region of the Garhwal Himalayas and is extensively covered by glaciers. We provide hydro‐meteorological insight into a severe storm that produced unusual high rains in June 2000 in the uppermost part of the Bhagirathi River. This storm was concentrated upstream of Gangotri town and triggered landslides/rockslides at several locations between the glacier snout and Gangotri town. One of the major rockslides blocked the Bhagirathi River at Bhujbas, about 3 km downstream of the Gangotri Glacier snout, creating an artificial lake at this location. High stream flow in the river, generated by rapid runoff response from mountain slopes along with melt runoff from the glacier, quickly increased the level of water stored in the artificial lake. Daily rainfall in this region rarely exceeds 10 mm, while total rainfall during this 6‐day storm was 131·5 mm. This unusual rain event occurred during the tourist season in June, consequently trapping a large number of tourists and vendors in this area. Sudden release of stored water generated floods that created havoc downstream of the artificially created lake. This paper presents the hydrological and meteorological information related to such an unusual and devastating event observed in the high altitude region of the Himalayas. Copyright © 2006 John Wiley & Sons, Ltd.     

GIS‐based regional landslide susceptibility mapping: a case study in southern California

Landslides threaten lives and property throughout the United States, causing in excess of $2 billion in damages and 25–50 deaths annually. In regions subjected to urban expansion caused by population growth and/or increased storm intensities caused by changing climate patterns, the economic and society costs of landslides will continue to rise. Using a geographic information system (GIS), this paper develops and implements a multivariate statistical approach for mapping landslide susceptibility. The presented susceptibility maps are intended to help in the design of hazard mitigation and land development policies at regional scales. The paper presents (a) a GIS‐based multivariate statistical approach for mapping landslide susceptibility, (b) several dimensionless landslide susceptibility indexes developed to quantify and weight the influence of individual categories for given potential risk factors on landslides and (c) a case study in southern California, which uses 11 111 seismic landslide scars collected from previous efforts and 5389 landslide scars newly digitized from local geologic maps. In the case study, seven potential risk factors were selected to map landslide susceptibility. Ground slope and event precipitation were the most important factors, followed by land cover, surface curvature, proximity to fault, elevation and proximity to coastline. The developed landslide susceptibility maps show that areas classified as having high or very high susceptibilities contained 71% of the digitized landslide scars and 90% of the seismic landslide scars while only occupying 26% of the total study area. These areas mostly have ground slopes higher than 46% and 2‐year, 6‐hour precipitation greater than 51 mm. Only 12% of digitized landslides and less than 1% of recorded seismic landslides were located in areas classified as low or very low susceptibility, while occupying 42% of the total study region. These areas mostly have slopes less than 27% and 2‐year, 6‐hour precipitation less than 41 mm. Copyright © 2007 John Wiley & Sons, Ltd.     

Emergency assessment of seismic landslide susceptibility： a case study of the 2008 Wenchuan earthquake affected area

The 8.0 Mw Wenchuan earthquake triggered widespread and large scale landslides in mountainous regions.An approach was used to map and assess landslide susceptibility in a given area. A numerical rating system was applied to five factors that contribute to slope instability. Factors such as lithology, topography, streams and faults have an important influence as event-controlling factors for landslide susceptibility assessment. A final map is provided to show areas of low,medium, and high landslide susceptibility. Areas identified as having high landslide susceptibility were located in the central,northeastern, and far south regions of the study area. The assessment results will help decision makers to select safe sites for emergency placement of refuges and plan for future reconstruction. The maps may also be used as a basis for landslide risk management in the study area.     

Analysis of landslide damage caused by the 2008 Wenchuan earthquake using strong motion data: A case study in the Beichuan county town

The county town of Beichuan county, China, experienced catastrophic destruction due to landslides induce by the 2008 Wenchuan earthquake. In consideration of the special location of the county town, this paper selected the landslides induced in the town as representative of large-scale near-rupture landslides, and quantitatively analyzed why the landslide damage was so destructive in the town by using strong motion data obtained from the Wenchuan earthquake in the Longmenshan area. Three methods were employed to estimate the landslide damage using strong motion data. (1) Peak ground accelerations (PGAs) on the hanging wall were used to evaluate the PGAs on the landslide sites in the town. The evaluated average PGAs were all greater than 1 g, indicating that the ground motion intensity was very strong during the earthquake. (2) Acceleration time histories, from another station with similar geological conditions to the town, were used to evaluate the critical acceleration changing range, and the estimated values showed the geological conditions were very susceptible to earthquakes. (3) Acceleration time histories, from two stations on the hanging and foot walls of the rupture, and near the town, were used to calculate the Newmark displacements, and all the evaluated displacements indicated that landslides were very likely. The results show that the slopes, susceptible to earthquakes in the Beichuan county town, were easily triggered under such strong ground-motion intensity and developed into large-scale catastrophic events.     

南海北部陆坡水合物分解引起海底不稳定性的定量分析

分析了天然气水合物分解引起海底斜坡不稳定性的原因,探讨了水合物分解引起沉积物层孔隙压力变化规律.以南海北部神狐海域水合物样品钻获区为研究对象,应用极限平衡法探讨了海底无限斜坡的稳定性问题,计算了设定的不同滑动面的安全系数,建立了目标不稳定区相关参数条件下的水合物分解与海底斜坡不稳定的模式图,模拟计算了不同程度的水合物分解对海底斜坡失稳的影响作用.结果表明：在假设条件下,南海神狐海域当水深为1200 m,沉积物层厚度为200 m,对于20°的较大坡角,沉积物层中5%水合物分解将引起海底斜坡失稳;斜坡坡角为5°时,沉积物层中15%水合物分解后,将会引起海底斜坡失稳;当斜坡坡角为3°或更小时,沉积物层中25%水合物分解后,将会引起海底斜坡失稳.     

The role of the seismic trigger in the Calitri landslide (Italy): historical reconstruction and dynamic analysis

The study covered by this paper was focused on the historical case of the Calitri landslide, which was repeatedly reactivated by earthquakes, as reported since 1694. The town of Calitri (Southern Italy) is located on a ridge whose southern slope, from its top to the Ofanto river valley floor, has been historically affected by major landsliding. The last record of recurrence of the Calitri landslide leads back to the 1980 Irpinia earthquake, which caused significant damage to the town and had pervasive and visible ground effects. Based on a detailed historical reconstruction of landsliding and seismicity at Calitri, the study analysed the current static and dynamic stability of the landsliding slope by means of a finite-difference numerical analysis, taking into account the various factors of landslide initiation and kinematics. The results of the numerical analysis: (i) were consistent with the roto-translational mechanism observed upon the latest reactivation of the landslide; (ii) demonstrated that excess pore pressure redistribution caused a lag between the seismic trigger and the initiation of landsliding; and (iii) showed the impact of seismic input frequency on propagation and depth of slope instability.     

Investigation of a landslide in the new site of Badong County by integrated geophysical survey

An integrated geophysical survey which combines vertical seismic profile method, shallow reflection seismic method, electric sounding, soil temperature measurement and radioactive gas measurement was used to investigate Zhaoshuling landslide in the new site of Badong County and to assess the stability of the landslide. By rational use of these methods together with borehole geological profile and other geological information, the spatial distribution of the landslide body, the formations and structures within and without the landslide body were determined and the stability of the landslide was also assessed, thus making great contribution to the successful and rational investigation and assessment of the landslide.     

地震动参数与地震灾害相关性分析——以汶川震区地震滑坡灾害为例

本文以汶川地震滑坡震害为例, 设计一种方法, 对几个反映不同地震动特性的地震动参数与地震滑坡灾害的相关性进行了分析比较.结果表明: Arias强度参数与地表破坏的相关性最好, 该参数比较适合小区域范围的震害预测评估; 峰值加速度与地表破坏的相关性较好, 但更适合作为较大区域的震害评估参数; 与持时和频率有关的参数对于具体场地的震害机理分析具有辅助作用; 垂向地震动对滑坡震害的作用不容忽视. 本文结论对于其它震害相关研究中评估因子的选取具有参考意义.      

龙门山地区类似2008年汶川大地震滑坡物质河流卸载时间的定量估算

定量研究地震滑坡物质河流卸载时间对理解地震与造山带地貌演化之间的关系有着十分重要的意义.本文以青藏高原东缘龙门山构造带内岷江流域为例,定量估算了2008年汶川大地震滑坡物质的河流卸载时间.研究结果表明,如果以位于龙门山构造带内的岷江河段现有搬运能力计算,并且岷江可以有效地搬运汶川地震滑坡物质,地震滑坡物质至少在3100 yr内被岷江卸载出龙门山.而龙门山构造带中段类似2008年汶川Ms8.0级大地震的复发周期约为3000 yr左右,暗示大地震所产生的滑坡物质量可以在大地震复发周期内基本上被侵蚀和剥蚀所平衡,并被卸载出龙门山构造带. 因此,我们推断:除了周期性大地震造成的地表抬升的累积外,龙门山地区地震及其它地表过程所产生的剥蚀物质通过河流快速卸载驱动了地壳均衡反弹和深部物质上涌,形成了青藏高原东缘的高陡地形梯度带. 相关的地球物理证据表明在青藏高原东缘可能存在由地表快速剥蚀(或侵蚀)所引发的地球深部地幔软流圈物质上涌.     

A chronology of post‐glacial landslides suggests that slight increases in precipitation could trigger a disproportionate geomorphic response

Large, deep‐seated landslides are common throughout the south‐eastern San Juan Mountains of Colorado and New Mexico, but their timing and initiation are not well understood. Determining when the landslides occurred would aid in clarifying the mechanisms for initiating landslides in the region and would help us to understand post‐glacial landscape evolution. We studied seven pre‐historic landslides located within the Tertiary volcanic rocks of the San Juan Volcanic Field. The landslides range in area from ~0.8 km² to ~11.3 km² and most are located in areas that were previously mapped as having been ice‐covered during the last glaciation. Landslide deposits were dated using a variety of methods including surface exposure dating (chlorine‐36, ³⁶Cl), radiocarbon dating of basal bog sediments and organic material buried in soils, and relative soil development. The resulting limiting ages range from approximately 14 ka to 2 ka and show that deep‐seated landsliding has occurred throughout the post‐glacial period. This broad range in ages is inconsistent with our initial hypothesis, which proposed that landslides were likely the result of debuttressing of glacial walls during glacial retreat. Furthermore, the timing of landslides does not seem to correlate with documented post‐glacial climatic shifts. Therefore, we conclude that landsliding in the region was the result of wetter than normal periods lasting months to years acting on weak bedrock preconditioned to failure and prepared by glacial debuttressing. Our findings suggest that the study area is likely still susceptible to deep‐seated landsliding and may become even more prone to large‐scale slope failure if future climate change increases precipitation in the San Juan Mountains. Copyright © 2017 John Wiley & Sons, Ltd.     

南海北部陆坡块体搬运沉积体系的地震响应与成因机制

块体搬运沉积体系是一种重力作用下形成的深水沉积体系,在全球大陆边缘沉积体系中扮演着重要角色.块体搬运沉积作用不仅造成危害极大的深水地质灾害,而且与海洋天然气水合物和深水油气的形成过程与富集有密切联系.根据新获得的海底地形地貌资料和地震资料,揭示了块体搬运沉积体系识别特征,明确了其分布范围.这些块体搬运沉积体系具有明显的滑坡形态和沉积构造;头部表现张性断裂构造,内部有旋转断块和流动构造,趾部表现为挤压和逆冲构造.块体搬运沉积体系表现出不同的成因类型.通过白云凹陷天然气水合物的分布模式和白云块体搬运沉积体系有限元数值模拟研究,认为白云块体搬运沉积体系与天然气水合物分解密切相关,进一步给出6种水合物分解模型情况下海底稳定性的安全因子,随着水合物分解量的增加,斜坡的稳定性逐渐减弱,当水合物的分解达到一定数量时,就会发育海底块体搬运沉积体系.     

Conodont diversification during the Ordovician: A perspective from North China and Tarim (Northwestern China)

Review of the literature on Ordovician conodont diversification in palaeoplates of North and Western China reveals that four diversity peaks are present in North China, occurring in the middle Tremadocian, early Floian, late Floian, and late Darriwilian, with three of these peaks (excepting that in the late Floian) also being recorded in Tarim. Three diversification intervals are present in North China, during the Tremadocian, late Floian, early and middle Darriwilian; comparable intervals are observed in the early and late Tremadocian, early Floian, and the Middle Ordovician in Tarim. The main conodont diversification episode in both palaeoplates took place in the Darriwilian, at the time of the Great Ordovician Biodiversification Event. A comparison of conodont diversity patterns in different palaeoplates (North China, Tarim, and South China) demonstrates that conodont radiation events mainly occurred within the Tremadocian, Floian, and Darriwilian. Conodont diversifications in these paleoplates also display some differences. In contrasting with Tarim and South China, North China witnessed a rapid conodont diversification during late Floian time. Conodont diversity in North China and Tarim increased continually and reached a peak in the late Darriwilian, concurrent with a prominent decreasing trend in South China. Differences of conodont diversification in these three palaeoplates may be related to their palaeogeography and tectonic history. When conodont diversifications in North China and Tarim are analysed on the background of palaeoenvironments, the main episodes are seen to be partly coincident with second order sea-level changes, particularly in North China. In general, conodont radiation correlates with large scale transgressions.     

Induced seismicity at wujiangdu reservoir,China: a case induced in the karst area

To date 19 cases of reservoir-induced seismicity have been acknowledged in China and 15 of them are associated with karst. The Wujiangdu case is a typical one induced in the karst area. The dam with a height of 165 m is the highest built in a karst area in China. Seismic activity has been successively induced in five reservoir segments seven months after the impoundment in 1979. A temporary seismic network consisting of 8 stations was set up in one of the segments some 40 km upstream from the dam. The results indicate that epicenters were distributed along the immediate banks, composed of karstified carbonate, and focal depths were only several hundred meters. Most of the focal mechanisms were of thrust and normal faulting. It is suggested that karst may be an important factor in inducing seismicity. It can provide an hydraulic connection to change the saturation and pressure and also weak planes for dislocation to induce seismicity.     

Mountain hydrology of Canada and China: A case study in comparative hydrology

Comparative hydrology attempts to identify regions with similar environmental attributes and then compares the hydrological activities in these regions to facilitate the transfer of knowledge and exchange of techniques. As a case study, the mountainous regions of Canada and China were compared. Vertical zonation is a characteristic feature of such regions, generating contrasts in microclimate, vegetation, soil and the resultant hydrological responses. An increase in precipitation with altitude is modified by aspect and other local factors. In temperate and colder latitudes, snow and ice are important, especially at higher elevations. Both countries have conducted many hydrological studies on snow and glaciers, but evaporation in mountainous terrain merits more attention. Runoff from mountainous catchments is often generated by a range of processes including rainfall, snowmelt and glacier melt, and runoff response to water input tends to be rapid. This study identifies some of the strengths and weaknesses of our current knowledge of mountain hydrology in both countries, and suggests that a more comprehensive treatment of the subject will improve the prediction of the hydrological behaviour of such regions.     

A quantitative approach to deep-water sedimentation in the South China Sea: Changes since the last glaciation

The first attempt is made to evaluate quantitatively the changes of accumulation rates in the South China Sea during the last glaciation and Holocene, based on the data of 72 sediment cores taken from six areas deeper than 100 m. As shown from the calculations, the accumulation rate during the last glaciation is much higher than that during the Holocene. The southern and northern continental slopes are distinguished from other areas by the highest accumulation rates, with different features of sedimentation for aifferent stages: The Glacial-Holocene contrast in accumulation rate of terrigenous material is more distinct in the southern slope, while the contrast in biogenic sedimentation rate is more remarkable in the northern slope. Project supported by the National Natural Science Foundation of China (Grant No. 49576268).     

A large landslide event in a post‐glacial landscape: rethinking glacial legacy

Threlkeld Knotts (c. 500 m above sea level) in the English Lake District has hitherto been considered to be a glacially‐modified intrusion of microgranite. However, its surface features are incompatible with glacial modification; neither can these nor the subsurface structures revealed by ground‐penetrating radar (GPR) be explained by post‐glacial subaerial processes acting on a glacially‐modified microgranite intrusion. Here we re‐interpret Threlkeld Knotts as a very large post‐glacial landslide involving the microgranite, with an estimated volume of about 4 × 10⁷ m³. This interpretation is tested against published and recent information on the geology of the site, the glacial geomorphic history of the area and newly‐acquired GPR data. More than 60 large post‐Last Glacial Maximum (LGM) rock–slope failures have significantly modified the glaciated landscape of the Lake District; this is one of the largest. Recognition of this major landslide deposit in such a well‐studied environment highlights the need to continuously re‐examine landscapes in the light of increasing knowledge of geomorphic processes and with available technology in currently active or de‐glaciating environments. Copyright © 2012 John Wiley & Sons, Ltd.