Quantitative Risk Assessment of Catastrophic Debris Flows through Numerical Simulation

The risk assessment is not only the one of the most effective soft measures in natural hazard prevention, but also is the base of hazard risk management. On account of the specificity of various elements at risk and debris flow mechanism, the theoretical system and technical procedure of debris flow quantitative risk assessment for buildings and roads were established in the mountaineous area of Southwest China, which included three sections: ①To represent debris flow hazard quantitatively using the intensity index IDF through FLO-2D simulation; ②To build debris flow physical vulnerability curve based on the loss exceedance-probability from Qipan gully debris flow case; ③To quantify the expected loss of the important elements at risk based on their database after setting the future debris flow scenarios. The case study of Yangling catchment indicated that the responding mechanism between elements at risk and debris flow physical mechanism was described quantitatively by this quantitative risk assessment system, which can contribute to the construction planning and prevention measure making in the southwestern mountainous area.     

西昆仑—帕米尔造山带及其北缘前陆盆地板内变形构造

笔者总结了西昆仑—帕米尔造山带及塔西南前陆盆地板内变形的各类构造模式、构造分带、新生代变形格局及构造演化,提出其新生代板内变形具有弧形构造分段性和阶段性演化的特点,发现了依格孜牙、柯克亚、桑株—杜瓦、卡兹克—阿尔特薄皮弧形推覆构造、齐姆根主弧形构造段及玉力群—克里阳构造段的三角带构造及叶尔羌—棋盘对冲过渡型弧形构造。认为对冲过渡型弧形构造及各弧形构造分段间的斜冲走滑带是塔西南前陆盆地板内变形的特殊产物。     

Late Cenozoic Deformation Sequence of a Thrust System along the Eastern Margin of Pamir, Northwest China

A thrust belt formed in the basin along the eastern margin of Pamir. The thrust belt is about 50 km wide, extends about 200 km, and includes three compressive structures from south to north: the blind Qipan structural wedge and Qimugen structural wedge, and the exposed Yengisar anticline. The thrust belt displays a right-stepping en echelon pattern. The Qipan structural wedge dies out northward to the west of the Qimugen structural wedge, and the Qimugen structural wedge dies out northward to the west of the Yengisar anticline. Detailed analysis of seismic reflection profiles of the western Tarim Basin reveal that fan-shaped growth strata were deposited in the shallow part of the thrust belt, recording the deformation sequence of the thrust belt. The depth of the Cenozoic growth strata decreases from south to north. The growth strata of the Qipan structural wedge is located in the middle-lower section of the Pliocene Artux Formation (N2a), the growth strata of the Qimugen structural wedge is close to the bottom of the Pleistocene Xiyu Formation (Q1x), and the growth strata of the Yengisar anticline is located in the middle section of the Xiyu Formation (Q1x). Combined with magnetostratigraphic studies in the western Tarim basin, it can be preliminarily inferred that the deformation sequence of the thrust belt along the eastern margin of Pamir is progressively younger northward. The geometry and kinematic evolution of the thrust belt in the eastern margin of Pamir can be compared with previous analogue modeling experiments of transpressional deformation, suggesting that the thrust belt was formed in a transpressional tectonic setting.     

Reef margin collapse, gully formation and filling within the Permian Capitan Reef: Carlsbad Caverns, New Mexico, USA

An area of reef margin collapse, gully formation and gully fill sedimentation has been identified and mapped within Left Hand Tunnel, Carlsbad Caverns. It demonstrates that the Capitan Reef did not, at all times, form an unbroken border to the Delaware Basin. Geopetally arranged sediments within cavities from sponge–algal framestones of the reef show that the in situ reef today has a 10° basinwards structural dip. Similar dips in adjacent back-reef sediments, previously considered depositional, probably also have a structural origin. Reoriented geopetal structures have also allowed the identification of a 200-m-wide, 25-m-deep gully within the reef, which has been filled by large (some  >15 m), randomly orientated and, in places, overturned blocks and boulders, surrounded by finer reef rubble, breccias and grainstones. Block supply continued throughout gully filling, implying that spalling of reef blocks was a longer term process and was not a by-product of the formation of the gully. Gully initiation was probably the result of a reef front collapse, with a continued instability of the gully bordering reef facies demonstrated by their incipient brecciation and by faults containing synsedimentary fills. Gully filling probably occurred during reef growth, and younger reef has prograded over the gully fill. Blocks contain truncated former aragonite botryoidal cements, indicating early aragonite growth within the in situ reef. In contrast, former high-magnesian calcite rind cements post-date sedimentation within the gully. The morphology of cavern passages is controlled by reef facies variation, with narrower passages cut into the in situ reef and wider passages within the gully fill. Gully fills may also constitute more permeable zones in the subsurface.     

昆明市东川区城市后山地区泥石流特征及防治

通过系统地对城市后山地区主要泥石流沟特征的分析,科学地选取治理工程措施,基本达到有效控制深沟泥石流物源的运移,减轻或消弱其它各沟泥石流危害的防治目标。通过削弱泥石流灾害的发育、发展,从而减轻地质灾害对东川市城区的威胁。     

塔西南叶城凹陷二叠系两套烃源岩特征及柯东1井油源分析

塔里木盆地西南坳陷叶城凹陷以二叠系为主力烃源岩,前人多按单一的海相或湖相烃源岩笼统分析,未考虑二叠系烃源岩不同组段及其沉积环境和沉积相带的差异。本文通过对叶城凹陷二叠系开展野外地质调查,结合该区钻井资料,首次将烃源岩分析精细到组,结果显示,叶城小区和和田小区二叠系分别以棋盘组和普司格组上段为主力烃源岩,但两者在分布和地化指标上有较大差异。其中棋盘组以浅海陆棚相为主,分布于凹陷西部的和什拉甫-莫莫克地区,烃源岩平均厚度大于100 m,总有机碳质量分数平均1.06%,类型为Ⅱ型,处于高-过成熟阶段。普司格组上段以湖相为主,分布于凹陷东部的普萨-杜瓦地区,烃源岩平均厚度大于200 m,总有机碳质量分数平均0.97%,类型为Ⅱ型和Ⅲ型之间,处于生油高峰阶段。二叠系这两套烃源岩具有较好的生烃能力,相比之下普司格组上段湖相烃源岩生烃潜力明显好于棋盘组浅海陆棚相。通过正构烷烃碳同位素比值和生物标志化合物分析,普司格组上段烃源岩为柯东1井原油的油源。结合储盖条件综合分析,叶城凹陷以甫沙-克里阳地区为油气勘探最有利区。     

Susceptibility mapping of gully erosion using GIS-based statistical bivariate models: a case study from Ali Al-Gharbi District,Maysan Governorate,southern Iraq

This work aims to evaluate the predictive capability of three bivariate statistical models, namely information value, frequency ratio, and evidential belief functions, in gully erosion susceptibility mapping in northeastern Maysan Governorate (Ali Al-Gharbi District) in southern Iraq. The gully inventory map, consisting of 21 gullies of different sizes, was prepared based on the interpretation of remotely sensed data supported by field survey. The gully inventory data (polygon format) were randomly partitioned into two sets: 14 gullies for build and training the bivariate model, and the remaining 7 gullies for validating purposes. Twelve gully influential factors were selected based on data availability and the literature review. The selected factors were related to lithology, geomorphology, soil, land cover, and topography (primary and secondary) settings. Analysis of factor importance using information gain ratio proved that out of 12 gully influential factors, eight were of more importance in developing gullies (the average merit was greater than zero). The most important factors and the training gully inventory map were used to generate three gully erosion susceptibility maps based on the three bivariate models used. For validation, the area under the operating characteristics curves for both success and prediction rates was used. The results indicated that the highest prediction rate of 82.9% was achieved using the information value technique. All the bivariate models had prediction rates greater than 80%, and thus they were regarded as very good estimators. The final conclusion was that the bivariate models offer advanced techniques for mapping gully erosion susceptibility.     

四川雷波碉楼沟泥石流特征及防治对策

碉楼沟泥石流沟为西苏角河左岸的一级支流,位于四川省雷波县西侧,流域面积0.85km~2,主沟长度1.6km,纵比降504.4‰。碉楼沟流域属构造侵蚀高中山地貌,呈叶状,支沟众多,主沟较少暴发泥石流。2015年5月7日碉楼沟暴发山洪灾害,造成8人死亡和严重财产损失,并对下游马颈子场镇居民的生命财产安全构成了威胁。在地质勘查的基础上,分析泥石流基本特征、形成条件,计算泥石流的重度、流速、一次泥石流总量等动力学参数。结合碉楼沟泥石流的特征和场镇社会、经济可持续发展的需要,提出防治方案,对该类泥石流沟谷的调查和防治具有一定实际意义。     

A GIS-based approach for gully erosion susceptibility modelling using bivariate statistics methods in the Ourika watershed,Morocco

Gully erosion is an important environmental issue with severe impacts. This study aimed to characterize gully erosion susceptibility and assess the capability of information value (InfVal) and frequency ratio (FR) models for its spatial prediction in Ourika watershed of the High Atlas region of Morocco. These two bivariate statistical methods have been used for gully erosion susceptibility mapping by comparing each data layer of causative factor to the existing gully distribution. Weights to the gully causative factors are assigned based on gully density. Gullies have been mapped through field surveys and Google earth high-resolution images. Lithofacies, land use, slope gradient, length-slope, aspect, stream power index, topographical wetness index and plan curvature were considered predisposing factors to gullying. The digitized gullies were randomly split into two parts. Sixty-five percent (65%) of the mapped gullies were randomly selected as training set to build gully susceptibility models, while the remaining 35% cases were used as validation set for the models’ validation. The results showed that barren and sparse vegetation lands and slope gradient above 50% were very susceptible to gully erosion. The ROC curve was used for testing the accuracy of the mentioned models. The analysis confirms that the FR model (AUC 80.61%) shows a better accuracy than InfVal model (AUC 52.07%). The performance of the gully erosion susceptibility map constructed by FR model is greater than that of the map produced by InfVal model. The findings proved that GIS-based bivariate statistical methods such as frequency ratio model could be successfully applied in gully susceptibility mapping in Morocco mountainous regions and in other similar environments. The produced susceptibility map represents a useful tool for sustainable planning, conservation and protection of land from gully processes.     

北京市密云县前火石岭泥石流沟形成条件及特征分析

北京地区现有泥石流沟856条,分布在北京北部燕山山脉和西部太行山脉一带,受地形地貌、地质条件、降雨条件以及人类活动影响较明显,总体以暴雨沟谷型泥石流为主。密云县前火石岭泥石流沟是燕山山脉一带典型的一条泥石流沟,文章在地质调查和勘查的基础上,从地质条件、地形地貌、降雨条件、人类活动等方面,综合分析前火石岭泥石流沟的形成条件及特征,同时对泥石流沟的发育情况进行深入剖析,按10年一遇暴雨强度的设计标准,在泥石流沟上游、中游、沟口3个断面计算泥石流运动特征参数,得出该泥石流沟为低易发-中等易发稀性水石流,目前处于发展阶段的停歇期,区域高强度集中降水为泥石流灾害的激发因素,泥石流的峰值流量等运动参数沿沟逐渐增大。分析结果对该泥石流沟的治理方案制定具有重要意义,对燕山山脉一带泥石流沟的防治具有借鉴作用。     

青海省格拉沟形成演化机制及其主要工程地质问题

格拉沟位于青海省内陆滩地，其形成演化反映了西北地区典型的水土流失过程。文章在收集大量野外资料的基础上，研究了格拉沟的形成演化机制，并对该沟道主要工程地质问题进行了探讨。分析认为，格拉沟形成演化是该地区特殊的内因外因共同作用的结果，基于此对其发育演化阶段进行了划分与预测。该沟主要工程地质问题为边坡稳定性、渗透稳定性、河流侵蚀等。其中边坡稳定性主要包括天然岸坡整体稳定性及崩塌、坠溜、滑塌等；渗透稳定性主要包括潜蚀与管涌；河流下切与溯源侵蚀则成为岸坡失稳破坏的重要诱发因素。探讨格拉沟形成演化机制及其主要工程地质问题，对于研究西北地区水土流失机理及其产生的环境问题具有一定的借鉴作用。     

北川县通口水电工程区岩溶发育特征探讨

研究区岩溶形态有溶沟、溶槽、溶斗、落水洞、溶蚀洼地以及大量的溶洞;影响岩溶发育主要因素有地层岩性、地质构造以及地貌。坝址区岩溶具有分带性特点;河床地带有利于岩溶的发育,坝址右岸和左岸岩溶发育存在差异。     

雅鲁藏布江下游色东普沟高位地质灾害发育特征遥感解译

色东普沟位于雅鲁藏布江下游左岸、加拉白垒峰下方,受温度、降水和地震的因素影响,曾多次发生高位地质灾害并造成雅鲁藏布江堵塞。通过实地调查,结合Landsat等多源、多期遥感影像以及InSAR雷达数据,对色东普沟高位地质灾害发育特征进行分析,并对现存变形体进行解译和分析,得到以下结论:色东普沟发育多处冰川、崩塌、滑坡和冰湖灾害;色东普沟自2001年起20年间,发生高位地质灾害堵塞雅鲁藏布江干流事件共5次;沟内上部极高山区现存确定变形体3处和疑似变形体2处;针对发生于2018年的两次色东普高位地质灾害,认为其物源来自于一处高位岩崩区和三处高位冰崩区。研究结果为色东普高位地质灾害的进一步研究提供了初步数据,并为类似地质灾害的研究提供了有效的科学思路。     

都江堰市龙池镇麻柳沟泥石流特征及形成条件分析

通过对都江堰市龙池镇麻柳沟泥石流灾害现场调查,分析了泥石流的特征及形成条件,并对沟道内松散固体物质储量进行了计算,分析了危险区范围。结果表明:麻柳沟流域的地形特征为泥石流形成提供了有利的地形条件,"5.12"汶川地震和"4.20"芦山地震为泥石流的形成提供了丰富的物源条件,多次强降雨为泥石流的启动提供了充足的水源条件。通过计算得出,麻柳沟沟道内的松散固体物质储量约为29.21×104 m3,其中形成区13.19×104 m3,流通区3.27×104 m3,堆积区12.75×104 m3,泥石流最大危险范围为0.247 1km2。     

Effects of gully erosion and gully filling on soil depth and crop production in the black soil region, northeast China

Gully erosion is a very serious problem in the black soil region of northeast China. Gully filling is often adopted for controlling gully erosion by local farmers and thus causes more serious soil erosion. In this study an ephemeral gully (EG, 74 m) and a classical gully (CG, 52 m) connected at the gully’s headcut were selected as the study site. Two comparisons were made to explore the effects of gully erosion and the subsequent gully filling on soil depth and soybean yield: (1) soil depth between 81 sample points in the study site and 11 reference points along the same slope with the gully; (2) soybean yield between 81 sample points in the study site and 30 baseline locations near the study site. The results indicated that gully erosion caused the reduction of soil depth and soybean yield. Although filling gullies with soil from adjacent areas seemed to be an expedient way to remediate the gullies, it resulted in substantial soybean yield reduction. Gully erosion reduced the soil depth and soybean yield in 74.4 and 83.9 % of the study site, respectively. The soybean yield reduction ratio was 34.5 % for the whole study site and 2.6 % for the black soil region. Soil depth was the most important soil property indicator to reduce yield. Every 1 cm decrease in soil depth in the areas adjacent to gullies due to infilling activities resulted in a 2 % decrease in yield. More significant was the deposition of sediment from gully erosion, which completely eliminated soybean yield. Currently, effective soil and water conservation measures are not known and adopted by local farmers extensively. In the future, once some measures for preventing soil erosion, in particular gully erosion, were proved effective, these technologies should be disseminated among local farmers.     

Geomorphology and GIS analysis for mapping gully erosion susceptibility in the Turbolo stream catchment (Northern Calabria, Italy)

This work summarizes the results of a geomorphological and bivariate statistical approach to gully erosion susceptibility mapping in the Turbolo stream catchment (northern Calabria, Italy). An inventory map of gully erosion landforms of the area has been obtained by detailed field survey and air photograph interpretation. Lithology, land use, slope, aspect, plan curvature, stream power index, topographical wetness index and length-slope factor were assumed as gully erosion predisposing factors. In order to estimate and validate gully erosion susceptibility, the mapped gully areas were divided in two groups using a random partitions strategy. One group (training set) was used to prepare the susceptibility map, using a bivariate statistical analysis (Information Value method) in GIS environment, while the second group (validation set) to validate the susceptibility map, using the success and prediction rate curves. The validation results showed satisfactory agreement between the susceptibility map and the existing data on gully areas locations; therefore, over 88% of the gullies of the validation set are correctly classified falling in high and very high susceptibility areas. The susceptibility map, produced using a methodology that is easy to apply and to update, represents a useful tool for sustainable planning, conservation and protection of land from gully processes. Therefore, this methodology can be used to assess gully erosion susceptibility in other areas of Calabria, as well as in other regions, especially in the Mediterranean area, that have similar morphoclimatic features and sensitivity to concentrated erosion.     

四川泸定县冷碛镇黑沟泥石流发育特征与危害初探

泸定冷碛镇黑沟流域内发育土层滑坡及土体蠕动变形体20处,为黑沟泥石流的主要松散物源;土层滑坡和土体蠕动变形体规模小,滑速慢,滑体结构松散,滑入溪沟易被洪流卷走,不会形成滑坡堰塞湖和溃决型泥石流。近60年来黑沟发生的最大一次泥石流,经计算泥石流流速为3．47m／s,峰值流量为122．79m^3／s,为大型泥石流,对沟谷两侧财产造成了巨大危害。     

齐姆根-桑株河地区石炭-二叠纪地层划分及对比

齐姆根-桑株河地区石炭-二叠系分布广泛,层位齐全,化石丰富.据实测剖面及系统采集的类及腕足、牙形石、孢粉等化石较准确地厘定了石炭-二叠系各地层单元界线和岩石组合特征,自下而上划分出卡拉巴西塔克组、克里塔克组、和什拉甫组、卡拉乌依组、阿孜干组、塔哈奇组和克孜里奇曼组、棋盘组、普司格组、达里约尔组、杜瓦组,其中下石炭统仅分布于莫莫克以西.早二叠世中晚期-晚二叠世早期新藏公路以东普司格组属河流-湖泊-冲积扇相沉积,莫莫克-齐姆根地区棋盘组,达里约尔组以浅海相与河流三角洲相交互沉积及湖泊-河流相沉积为特征,晚二叠世晚期仅于新藏公路以东沉积冲积扇-扇三角洲相的杜瓦组.     

滨浅海泥流沟谷识别标志、类型及沉积模式——以莺歌海盆地东方1-1气田为例

在滨浅海沉积环境中有一类特殊的重力流水道沉积,名为泥流沟谷（mud flow gully）。泥流沟谷以泥岩充填为主,呈正韵律,厚度中等,往往切割其下部的砂体。在垂向上表现为泥流沟谷之下多为临滨或滨外的砂坝与滩砂,其上多为滨外泥沉积。泥流沟谷主要形成于滨浅海地形转折之处,由于构造事件的影响,导致塑性的尚未固结成岩的泥质沉积产生滑动,形成一种形态上类似下切河道的沟谷,在地形平缓之处,这些泥流又发生汇聚形成前端连片分布的特征。按泥流冲沟切割砂体的规模,可细分为“深”、“中”、“浅”三种类型,其中“深沟谷”表现为“深而宽”的特征,发育在地形坡折带,下切程度强;而“浅沟谷”呈现“浅而窄”的特点,发育在地形上游平缓带,下切程度弱;“中沟谷”下切深度介于“深”、“浅”两种沟谷之间,下切程度中等。泥流沟谷是储集砂体的侧向渗流屏障,浅沟谷往往分布在砂体中心部位,深沟谷分布在砂体边缘,中沟谷处于二者之间。受泥流沟谷的影响,砂坝砂体呈孤立状分布,同时由于夹层的影响使得砂体横向及垂向连续性与连通性变差。     

Soil erosion on a sub-tropical coastal dune complex,Transkei, Southern Africa

A fossil dune complex on the east coast of southern Africa is presently undergoing extensive accelerated erosion, with concomitant dune reactivation and degradation, unconfined erosion (sheetwash and wind deflation) and extensive development of V-shaped, ravine-type gully forms on hillslopes composed of thick sequences of Quaternary (Berea Formation?) dune sands. The sands comprise a thick, reddened, ferralitic sand carapace overlying white, poorly cemented quartzitic sands. Soil erosion has resulted from degradation of the red dune sand cover. Despite the cohesionless nature of the host materials, gully forms developed on dune sands are typologically similar to those developed in regolith or soft bedrock. This demonstrates that gully forms are influenced by the degree of homogeneity, rather than the absolute strength, of the host material subject to erosion. Factors which have contributed to erosion are discussed.