Landslides triggered by the 2016 Mj 7.3 Kumamoto,Japan, earthquake

The aim of this study is to establish a detailed and complete inventory of the landslides triggered by the Mj 7.3 (Mw 7.0) Kumamoto, Japan, earthquake sequence of 15 April 2016 (16 April in JST). Based on high-resolution (0.5–2 m) optical satellite images, we delineated 3,467 individual landslides triggered by the earthquake, occupying an area of about 6.9 km². Then they were validated by aerial photographs with very high-resolution (better than 0.5 m) and oblique field photos. Of them, 3,460 landslides are distributed in an elliptical area about 6000 km², with a NE-SW directed 120-km-long long axis and a 60-km-long NW-SE trending short axis. Most of the landslides are shallow, disrupted falls and slides, with a few flow-type slides and rock and soil avalanches. The analysis of correlation between the landslides and several control factors shows the areas of elevation 1000–1200 m, stratum of Q₃-Hvf, seismic intensity VIII and VIII+, and peak ground acceleration (PGA) 0.4–0.6 g register the highest landslide abundance. This study also discussed the relationship between the spatial pattern of the landslides and the seismotectonic structure featured by a strike-slip fault with a normal component and the volcanism in the study area.     

Destructive near-fault strong ground motion from the 2016 Kumamoto prefecture,Japan, M7.3 earthquake

The sequence of the 2016 Kumamoto, Japan, earthquake, which included an initial M6.5 foreshock on April 14, followed by a larger M7.3 mainshock on April 16, and subsequently occurred high aftershock activity, caused significant damage in Kumamoto and neighboring regions. The near-field strong motion record by strong motion network (K-NET and KiK-net) and the intensity meter network demonstrated clearly the characteristics of the strong ground motion developed by the shallow (H = 12 km), inland earthquake comprising short-time duration (<15–20 s) but large (>1G) ground accelerations. The velocity response spectra of the near-fault motion at Mashiki and Nishihara showed large levels (>300–550 cm/s) in the short-period range (T = 1–2 s), several times larger than that of the near-field record of the destructive 1995 Kobe earthquake (M7.3) and that of the 2004 Mid-Niigata earthquake (M6.8). This period corresponds to the collapse vulnerability of Japanese wooden-frame houses, and is the major cause of severe damage during the Kumamoto earthquake. The response spectra also showed extremely large levels (>240–340 cm/s) in the long-period (T > 3 s) band, which is potentially disastrous for high-rise buildings, large oil storage tanks, etc. to have longer resonant period. Such long-period motion was, for the most parts, developed by the static displacement of the fault movement rather than by the seismic waves radiating from the source fault. Thus, the extreme near-fault long-period motion was hazardous only close to the fault but it attenuated very rapidly away from the fault.     

A new approach to analysis of landslide slope stability

This paper is based on data from engineering-geological research on the landslide slopes of the Moscow River valley from the site of a proposed bridge crossing reconstruction. A method for delineating the slippage surface is suggested, which allows a more reliable evaluation of landslide stability and pressure for planning and decision-making purposes during the reconstruction of the bridge crossing, and an appropriate mitigation strategy.     

滑坡稳定性计算和滑坡稳定性量化评分方法的适用性对比研究——以湖南衡东某风电场公路切坡为例

拟以湖南衡东某风电场公路切坡为例,对比分析了公路切坡稳定性评价常用的两种分析方法,即滑坡稳定性计算和滑坡稳定性量化评分,以具体的工程项目为案例,依据公路切坡引发滑坡的地质环境条件,应用两种方法对该切坡可能形成的滑坡进行了对比分析。研究表明:对于勘查程度较高的大型滑坡稳定性评价,采用滑坡稳定性定量计算方法,结论较为准确;对于勘查程度较低的中小型滑坡稳定性评价,采用滑坡稳定性量化评分法,可减少工作量,结论较为准确;对于为大型且地质环境条件复杂,建议用两种方法相互论证,结论可信度高。     

永吉高速公路黑潭坪边坡三维稳定性研究

通过对永吉高速公路黑潭坪边坡的野外调查,详细地了解了研究区工程地质条件,探讨了边坡变形破坏机理,结合室内试验和计算反演获取岩土体强度参数,在此基础上建立三维地质模型,运用FLAC3D数值分析软件采用强度折减法对不同工况下的坡体稳定性进行详细分析并提出治理建议。研究表明:(1)边坡变形破坏是内外因素综合作用的结果,岩土体性质不良是边坡变形破坏的内在因素,坡脚便道开挖和地表水下渗是边坡变形破坏的诱导因素;(2)强度折减法应用于边坡三位稳定性分析具有较好的适用性;(3)数值模拟显示采用削坡结合锚固的综合治理措施具有明显的效果。     

Geomorphology and landslide susceptibility assessment using GIS and bivariate statistics: a case study in southern Italy

In this article, the results of a study aimed to assess the landslide susceptibility in the Calaggio Torrent basin (Campanian Apennines, southern Italy) are presented. The landslide susceptibility has been assessed using two bivariate-statistics-based methods in a GIS environment. In the first method, widely used in the existing literature, weighting values (Wi) have been calculated for each class of the selected causal factors (lithology, land-use, slope angle and aspect) taking into account the landslide density (detachment zones + landslide body) within each class. In the second method, which is a modification of the first method, only the landslide detachment zone (LDZ) density has been taken into account to calculate the weighting values. This latter method is probably characterized by a major geomorphological coherence. In fact, differently from the landslide bodies, LDZ must necessarily occur in geoenvironmental classes prone to failure. Thus, the calculated Wi seem to be more reliable in estimating the propensity of a given class to generate failure. The thematic maps have been reclassified on the basis of the calculated Wi and then overlaid, with the purpose to produce landslide susceptibility maps. The used methods converge both in indicating that most part of the study area is characterized by a high–very high landslide susceptibility and in the location and extent of the low-susceptible areas. However, an increase of both the high–very high and moderate–high susceptible areas occurs in using the second method. Both the produced susceptibility maps have been compared with the geomorphological map, highlighting an excellent coherence which is higher using method-2. In both methods, the percentage of each susceptibility class affected by landslides increases with the degree of susceptibility, as expected. However, the percentage at issue in the lowest susceptibility class obtained using method-2, even if low, is higher than that obtained using method-1. This suggests that method-2, notwithstanding its major geomorphological coherence, probably still needs further refinements.     

Statistical evaluation of the effect of earthquake with other related factors on landslide susceptibility: using the watershed area of Shihmen reservoir in Taiwan as a case study

Landslide susceptibility evaluation is one of the most important issues in watershed management. After an earthquake, the landslide susceptibility decreases functionally with increases in the distance from the epicenter. Under the same rainfall intensity, landslides are more likely to occur in an area where earthquakes occur more frequently. However, the questions of how much an earthquake should be weighted and how to evaluate the effects of an earthquake still need to be studied. To understand how earthquakes affect rainfall-triggered landslides, the horizontal peak ground acceleration (PGA) data from the Central Weather Bureau Seismic Network is used as the earthquake factor and combined with other factors to determine the weight of earthquakes in landslide susceptibility using logistic regression. The results indicate that the ability of landslide prediction is better when considering the earthquake factor. This study also proved that although there are no co-seismic landslides (after earthquakes) in the study area, the earthquake factor is still required to increase the model accuracy. PGA has been described as a usable factor. In areas with frequent earthquakes and high geological activity, when using historical data to evaluate landslide susceptibility, the earthquake factor should be taken into consideration to prevent errors.     

Modelling of 2016 Kumamoto earthquake by integrating site effect in semi-empirical technique

Natural Hazards - The 2016 Kumamoto earthquake (MJMA7.3) struck central area of Kyushu Island, Japan. The presence of near surface low velocity layer greatly amplified the ground motions and caused...     

基于地震传播过程的滑坡动力稳定性分析

当进行滑坡地震稳定性分析时,一般对滑体取某一固定的加速度,这忽略了地震波的传播过程。滑坡在地震中破坏的根本原因是地震波在岩土体中传播时,在滑体和滑床间形成了加速度差。推导了加速度差的计算公式,以青海省玉树机场路3号滑坡为原型,以玉树机场强震观测台的实测加速度时程为动力输入,采用传递系数法计算滑坡动力稳定系数时程曲线。结果表明,天然状态滑坡的稳定系数为1.269,最小动力稳定性系数为0.962,最小平均稳定系数为1.069。滑坡的整体稳定性较好,不会形成整体失稳,但会有局部变形,与震后实测现象一致。     

Neural networks and landslide susceptibility: a case study of the urban area of Potenza

For those working in the field of landslide prevention, the estimation of hazard levels and the consequent production of thematic maps are principal objectives. They are achieved through careful analytical studies of the characteristics of landslide prone areas, thus, providing useful information regarding possible future phenomena. Such maps represent a fundamental step in the drawing up of adequate measures of landslide hazard mitigation. However, for a complete estimation of landslide hazard, meant as the degree of probability that a landslide occurs in a given area, within a given space of time, detailed and uniformly distributed data regarding their incidence and causes are required. This information, while obtainable through laborious historical research, is usually partial, incomplete and uneven, and hence, unsatisfactory for zoning on a regional scale. In order to carry this out effectively, the utilization of spatial estimation of the relative levels of landslide hazard in the various areas was considered opportune. These areas were classified according to their levels of proneness to landslide activity without taking recurrence periods into account. Various techniques were developed in order to obtain upheaval numerical estimates. The method used in this study, which was applied in the area of Potenza, is based on techniques derived from artificial intelligence (Artificial Neural Network—ANN). This method requires the definition of appropriate thematic layers, which parameterize the area under study. These are recognized by means of specific analyses in a functional relationship to the event itself. The parameters adopted are: slope gradient, slope aspect, topographical index, topographical shape, elevation, land use and lithology.     

Microtremor survey and stability analysis of a soil-rock mixture landslide: a case study in Baidian town,China

Soil-rock mixtures (S-RM) are widely distributed in mountainous regions, and there are different genetic types and scales of S-RM slopes. The stability of these slopes is very important for slope safety during the construction and operation of engineering projects. Since the mechanical properties of an S-RM are mainly dominated by its random component, accurately investigating the structure of an S-RM slope is the fundamental basis for evaluating the mechanism of a landslide. In this paper, in situ direct shear tests are used to obtain the “soil” strength parameters of the S-RM, the microtremor survey method (MSM) is introduced to detect the S-RM slope and the numerical method of FEM is utilised to simulate the failure characteristics and stability of the S-RM slope. Based on the MSM, the strata structure and proportions of solitary rock blocks in the S-RM slope are investigated, and three possible models of the S-RM slope are established. By using the strength reduction method in numerical simulations, the potential failure surface and stability of a slope of homogeneous soil and that with solitary rock blocks are discussed. The study results show that the MSM is an effective method to estimate the proportion of rock blocks in the S-RM slope. The presence of solitary rock blocks makes the slope potential slide surface complicated. The factor of safety of the S-RM slope is higher than that of the homogeneous soil slope, the rock blocks at the toe of the slope are favourable for slope stability and the rock blocks near the surface of the slope squeeze the lower soil and improve the safety factor of the slope.     

Accuracy assessment of InSAR derived input maps for landslide susceptibility analysis: a case study from the Swiss Alps

In recent years SAR interferometry has become a widely used technique for measuring altitude and displacement of the surface of the earth. Both these capabilities are highly relevant for landslide susceptibility studies. Although there are many problems that make the use of SAR interferometry less suitable for landslide inventory mapping, it’s use in landslide monitoring and in the generation of input maps for landslide susceptibility assessment looks very promising. The present work attempts to evaluate the usefulness and limitations of this technique based on a case study in the Swiss Alps. Input maps were generated from ERS repeat pass data using SAR interferometry. A land cover map has been generated by image classification of multi-temporal SAR intensity images. An InSAR DEM was generated and a number of maps were derived from it, such as slope-, aspect, altitude- and slope form classes. These maps were used to generate landslide and rockfall susceptibility maps, which give fairly well acceptable results. However, a comparison of the InSAR DEM with the conventional Swisstopo DEM, indicated significant errors in the absolute height and slope angles derived from InSAR, especially along the ridges and in the valleys. These errors are caused by low coherence mostly due to layover and shadow effects. Visual comparison of stereo images created from hillshading maps and corresponding DEMs demonstrate that a considerable amount of topographic details have been lost in the InSAR-derived DEM. It is concluded that InSAR derived input maps are not ideal for landslide susceptibility assessment, but could be used if more accurate data is lacking.     

Hill slope stability analysis using two and three dimensions analysis: A comparative study

Slope instability is very common phenomenon, especially in tectonically active hills of the lesser Himalaya. The deformed, weathered and fragile rocks of the lesser Himalaya are often vulnerable under natural or anthropogenic influences. There were several cases of slope failure along highway sections in Uttarakhand Himalaya. The study was carried out along a highway section of NH-109. The factor of safety (FoS) is commonly most acceptable parameter that analyses the health of slopes. The two dimensional (2D) numerical analysis techniques are commonly used to obtain the FoS. It is observed that many times FoS obtained from 2D analysis techniques do not qualify the actual conditions and are usually lower in value as compared to ground conditions. This, in turn, increases the cost of remedial measures used for protection of slopes. This paper presents a comparative study of 2D and 3D numerical analysis based on the finite difference method (FDM) using fast Langrangian analysis of continua (FLAC) codes. The study indicates that there is no appreciable difference between FoS values obtained from 2D and 3D analysis based on the selected slope conditions. The difference ranges from 0.02 to 0.07 for analysed cases in uniform rock mass. The study also exhibits some of the important analytical observations and effects of variables on resultant FoS.     

Prediction on landslide displacement using a new combination model: a case study of Qinglong landslide in China

Prediction on landslide displacement plays an important role in landslide early warning. Many models have been proposed for this purpose. However, the accuracy of the prediction results by these models often varies under different conditions. Rational evaluation and comprehensive consideration of these results still remain a scientific challenge. A new comprehensive combination model is proposed to predict the landslides displacement. The elementary displacement prediction is made by the support vector machine model, the exponential smoothing model, and the gray model (GM)(1,1). The results of the models are comprehensively evaluated by combining the results and introducing the accuracy matrix. The optimal weight in the evaluation work is obtained. A rational prediction result can be attained based on the so-called combination model. The proposed method has been tested by the application of Qinglong landslides in Guizhou Province, China. The comparison between the prediction results and in situ measurement shows that the prediction precision of the proposed model is satisfactory. The root-mean-square error (RMSE) of the combination model can be reduced to 1.4316 (monitoring site JCK2), 1.2623 (monitoring site JCK4), 2.3758 (monitoring site JCK6), 2.2704 (monitoring site JCK8), 1.4247 (monitoring site JCK11), and 0.9449 (monitoring site JCK12), which is much lower than the RMSE of the individual models.

     

Combined methodology for three-dimensional slope stability analysis coupled with time effect: a case study in Germany

High-steep slopes in open pit mines are much more likely to collapse due to mining operations. Challenges such as data acquisition, precise numerical models and adaptable methodologies have impeded more reliable results of slope stability analysis based on the current methods. Within this context, this paper proposes a combined methodology using light detection and ranging technology to capture high-resolution slope geometry, three-dimensional geological and geotechnical modeling technologies for creating high-quality numerical simulation models and finite-element slope stability analyses combined with a new automatic strength reduction technique to analyze complex geotechnical problems. At the end, the methodology introduces a time series analysis to improve the reliability of the calculated factor of safety. A case study in the deepest open pit mine in Hambach, Germany, was conducted to test and demonstrate the effectiveness and applicability of the proposed methodology.     

气温变化对多年冻土斜坡稳定性的影响

受气温变化影响,浅层冻土滑坡失稳涉及水分的固液相态转换,是一个复杂的水热力耦合过程。为揭示气温变化对多年冻土斜坡稳定性的影响,基于冻土水热力耦合数值模型,模拟了2020—2024年青海省多年冻土区斜坡水热力演化过程。研究结果表明：水分迁移速率呈周期性变化,每年5—10月活动层融化程度高,总体积含水率变化趋势显著;夏季多年冻土上限以下的高含冰量土层融化产生厚度约15 cm的富水层,孔隙水压难以消散;4年间多年冻土上限下移10.4 cm,导致活动层和富水层的厚度增大,上覆融土下滑力增大、抗滑力减小,土体抗剪强度进一步下降;活动层土体每年产生数厘米冻胀融沉变形,抗剪强度不断劣化,坡脚处最容易形成薄弱带。     

地震诱发滑坡的快速评估方法研究:以2017年MS 7.0级九寨沟地震为例

山岳地区强烈地震诱发的滑坡、崩塌等地震次生灾害在造成严重人员伤亡的同时,对社会经济的发展也构成了严重威胁。而震后滑坡分布的快速评估,尤其是滑坡重灾区的确定,则可为救援工作的科学部署和有效开展提供决策支持并减轻地震灾害的损失。2017年8月8日发生于四川省阿坝州九寨沟风景区的MS 7.0级地震诱发了大量的滑坡、崩塌灾害,造成了一定的人员伤亡和财产损失,凸显出进行震后滑坡快速评估的重要性。本文通过对九寨沟地震灾区震前、震后“北京二号”遥感影像的对比分析,解译此次地震诱发的滑坡分布概况。尽管震后影像在局部区域有云团覆盖,影响了震区滑坡解译的详尽程度,但是对于主要发生的滑坡地震高烈度地区(≥Ⅻ度),本文所用影像基本满足解译要求。本文共解译出194个面积大于700 m2的滑坡,这些滑坡主要沿地震烈度长轴方向分布,灾害体平面面积达5.6 km2,影响范围超过600 km2。通过对九寨沟地震灾区的地形、岩性及地震动加速度进行分析,本文采用Newmark刚体滑块模型对该区震后滑坡危险区域进行了预测。预测结果按照危险程度不同划分为5个级别,即高度危险、较高危险、中度危险、较低危险和低度危险。滑坡分布与评估结果呈现出较好的一致性:解译的滑坡主要分布在评估为滑坡高度危险的区域,表明本文所采用方法的有效性。本文对该方法的局限性也进行了讨论,并提出改进建议。     

Mapping method of rainfall-induced landslide hazards by infiltration and slope stability analysis

Landslides - By utilizing the Green-Ampt infiltration equation and the infinite slope stability model, a method for analyzing shallow slope failures caused by rainfall is developed. With rainfall...     

Back analysis of landslide susceptibility zonation mapping for the 2005 Kashmir earthquake: an assessment of the reliability of susceptibility zoning maps

The October 2005 earthquake triggered several thousand landslides in the Lesser Himalaya of Kashmir in northern Pakistan and India. Analyses of ASTER satellite imagery from 2001 were compared with a study undertaken in 2005; the results show the extent and nature of pre- and co-/post-seismic landsliding. Within a designated study area of ~2,250 km², the number of landslides increased from 369 in 2001 to 2,252 in October 2005. Assuming a balanced baseline landsliding frequency over the 4 years, most of the new landslides were likely triggered by the 2005 earthquake and its aftershocks. These landslides mainly happened in specific geologic formations, along faults, rivers and roads, and in shrubland/grassland and agricultural land. Preliminary results from repeat photographs from 2005 and 2006 after the snowmelt season reveal that much of the ongoing landsliding occurred along rivers and roads, and the extensive earthquake-induced fissuring. Although the susceptibility zoning success rate for 2001 was low, many of the co-/post-seismic landsliding in 2005 occurred in areas that had been defined as being potentially dangerous on the 2001 map. While most of the area in 2001 was (very) highly susceptible to future landsliding, most of the area in 2005 was only moderate to low susceptible, that is, most of the landsliding in 2005 actually occurred in the potentially dangerous areas on the 2001 map. This study supports the view that although susceptibility zoning maps represent a powerful tool in natural hazard management, caution is needed when developing and using such maps.     

地震作用下岩羊村滑坡稳定性与失稳机制研究

以云南香丽高速公路沿线的岩羊村滑坡为研究对象,开展了滑坡动力稳定性评价及失稳机制研究:进行了不同烈度地震下的滑坡稳定性分析,采用滑带弹性区体积占比的变化反映其失稳过程,结合滑坡变形破坏模式,对滑坡整体稳定性进行评价;针对极限地震工况,分别从时间和空间角度描述滑坡失稳过程;建立了同时考虑滑带弱化和硬化的滑坡尖点突变模型,揭示了滑坡失稳的触发机制。研究表明:滑坡在区域Ⅷ度地震烈度条件下基本保持稳定,在锁固段的"锁固作用"下滑坡仅发生局部破坏;滑坡发生整体失稳的临界峰值加速度为2.29 m/s²,其失稳机制为在前缘牵引、后缘拉裂作用下,滑带塑性区贯通导致的整体失稳;地震作用下滑带前缘、中部、后缘并非同步破坏,表现为累积-触发效应;利用改进尖点突变模型推导了刚度效应失稳判据,揭示了滑坡整体稳定性与滑带介质的刚度及尺寸特性密切相关。研究结果为岩羊村滑坡的防治与抗震设计提供了指导,并可为同类工程的动力稳定性评价与失稳机制分析所借鉴。