Development and application of Shannon’s entropy integrated information value model for landslide susceptibility assessment and zonation in Sikkim Himalayas in India

Natural Hazards - The state of Sikkim in India has many steep slopes and has been susceptible to landslides. Since 1968 there have been innumerable losses of lives and properties due to landslides....     

Landslides and neotectonic activities in the Main Boundary Thrust (MBT) zone: Southeastern Kumaun,Uttarakhand

Main Boundary Thrust (MBT) zone is constituted of some of the landslide prone areas in southeastern part of Kumaun Sub-Himalaya. Role of landslides as natural hazard and hill slope modifying agent is well documented from various part of Himalayan region and southern hills of Kumaun particularly in the MBT zone, which are susceptible to various type of mass movement. The rocks making up the slopes has been put to a number of brittle deformation phases during the movement along the MBT, and are traversed by number of joint sets. In the open slope these intersecting joint sets forms wedges and are the most favorable site for initiation of rockfalls and other types of landslides. Landslides are taking place primarily due to high angle slopes, formation of structural wedges along the free steep slopes, sheared nature of the rocks due to proximity to the MBT and neotectonic activities along the MBT and other transverse faults. Wedge failure is a common type of landslides in rock slopes characterized by multiple joints and acts as sliding planes for the failed blocks. Field observations and wedge failure analysis indicates most of the landslides taking place in MBT zone of Kumaun Sub-Himalaya are joint controlled. Safety Factor analysis suggests MBT zone of Kumaun Sub-Himalayan region is prone to landslides and related mass movements. This zone is also neotectonically active as indicated by various geomorphic signatures such as structurally controlled drainage pattern, offsetting of fan by MBT and formation of number of small lakes.     

厦门市崩塌滑坡灾害的发育特征及防治建议

区内工程地质灾害主要为崩塌、滑坡和不稳定斜坡,灾害的形成与发展受自然因素和人类经济活动的影响。基于调查资料,系统分析区内地质灾害类型及发育规律。最后针对灾害发育特征提出相应的防治措施和建议。     

Macroseismic field observations of 18 September 2011 Sikkim earthquake

A shallow-focus damaging earthquake of magnitude 6.9?Mw struck the Sikkim Himalaya, north-east India, on 18 September 2011 at 12:40:48 UTC (06:10:48PM IST). The epicentre was located north-west of Chungthang on Indo-Nepal border of Sikkim Himalaya. The earthquake was widely felt in northern India and caused widespread damage to poorly built and framed structures in Sikkim region, northern Bihar, eastern Nepal, southern Bhutan and part of Tibet adjoining Sikkim Himalaya. A lot of secondary effects in the form of landslides, rockfalls and landslide lake outburst flood were caused due to strong shaking effect of the earthquake. Maximum intensity IX according to the European Macroseismic Scale-98 was observed in the meizoseismal zone surrounding Chungthang village. Asymmetrical distribution and heterogeneous damage pattern demonstrate intensity attenuation characteristics of the region. Although the regional tectonic framework of Sikkim region indicates compressional thrust tectonics regime, according to CMT fault-plane solution this earthquake involved predominantly strike-slip motion on a steep fault. Unlike Nepal and north-west Himalaya where microseismicity and large earthquakes indicate thrust mechanism, this Sikkim earthquake suggests that strike-slip principal component may imply transcurrent deformation.     

Modeling and risk assessment of landslides using fuzzy logic. Application on the slopes of the Algerian Tell (Algeria)

Natural risk regains the notion of exposure to natural disaster or dangers of any natural hazard. Its management consists in the assessment and the anticipation of risks, as well as to the setting up of an alert system. From natural risk, we mentioned one bound to landslides in natural slopes that are difficult to surround and approach. Nevertheless, the assessment of landslides risk is the object of several works of research and many models, based on the multicriteria analysis, have been established. It should be noted that based on multicriteria approach, we evaluated, in a previous work, the landslide risk using the weighted sum model. The results reveal that the use of qualitative parameters influenced the classification of slope. This led us to adopt fuzzy logic approaches for assessment. This work examines the contribution of fuzzy sets theory to modeling and assessment of landslides risk in natural slopes. It brought to use this approach that permits the survey of these imprecision in adopting a Mamdani model. The method has been applied on slopes, situated in four areas of the Algerian Tell, where each is characterized by the different natural conditions. The result, put in evidence, summarizes modeling and risk assessment of landslides in an optimal classification of slopes according to the degree of instability risk. It allows decision makers to put in strategies for possible work of these slopes.     

History of landslide susceptibility and a chorology of landslide-prone areas in the Western Ghats of Kerala,India

Kerala is the third most densely populated state in India. It is a narrow strip of land, of which 47% is occupied by the most prominent orographic feature of peninsular India, The Western Ghats mountain chain. The highlands of Kerala experience several types of landslides, of which debris flows are the most common. They are called “Urul Pottal” in the local vernacular. The west-facing Western Ghats scarps that runs the entire extent of the mountain system is the most prone physiographic unit for landslides. The highlands of the region experience an annual average rainfall as high as 500 cm through the South-West, North-East and Pre-Monsoon showers. A survey of ancient documents and early news papers indicates a reduced rate of slope instability in the past. The processes leading to landslides were accelerated by anthropogenic disturbances such as deforestation since the early 18th century, terracing and obstruction of ephemeral streams and cultivation of crops lacking capability to add root cohesion in steep slopes. The events have become more destructive given the increasing vulnerability of population and property. Majority of mass movements have occurred in hill slopes >20° along the Western Ghats scarps, the only exception being the coastal cliffs. Studies conducted in the state indicates that prolonged and intense rainfall or more particularly a combination of the two and the resultant pore pressure variations are the most important trigger of landslides. The initiation zone of most of the landslides was typical hollows generally having degraded natural vegetation. A survey of post-landslide investigation and news paper reports enabled the identification of 29 major landslide events in the state. All except one of the 14 districts in the state are prone to landslides. Wayanad and Kozhikode districts are prone to deep seated landslides, while Idukki and Kottayam are prone to shallow landslides.     

Understanding rainfall-landslide relationships in man-modified environments: a case-history from Caramanico Terme, Italy

 The expansion of Caramanico Terme in this century has led to the urbanization of marginally stable valley slopes, and this has coincided with the apparent acceleration of landslide processes. Recent landslides on man-modified slopes were caused, but not necessarily triggered, by heavy precipitation (antecedent moisture was a more critical factor than the amount of storm rainfall). Because no important landslides on natural slopes in the same period were reported in the Caramanico area, a clear distinction must be made between natural settings and those modified by man when determining rainfall thresholds for predictive purposes. In recently urbanized mountainous environments, the thresholds used to assess landslide hazards should not be weighted too heavily on old historical records of precipitation and associated mass movements. Instead, more weight ought to be given to the period following the occurrence of any major anthropogenic and natural (e.g. high-magnitude earthquake) modification of slope setting. Received: 19 October 1996 · Accepted: 25 June 1997     

The landslides in the Three Gorges Reservoir Region,China and the effects of water storage and rain on their stability

According to the statistics, there were about 1,736 landslides with the total volume of 1.339 × 10¹¹ m³ in the 100 km² area of upper reaches of the Yangtze River, in which about 94% of landslides are triggered by rain and water storage. Thus, based investigation of the results of the landslides in this region, this paper completed a systematic study on the effects of rainfall and water storage on the landslides in the region and found that the distribution of landslides over time and space are well correlated with the precipitation distribution in this region; landslides are also strictly controlled by the stratum, geological structure, river valley form, shore type, etc. Meanwhile, the pattern of water table variation of the three gorges reservoir will do have very serious impacts on the stability of the slopes in this region. All research results show that water storage and rainfall are the two important inducing factors that can cause a lot of large-scale landslides. Therefore, some effective control measures for water storage and rainfall should be taken so as to minimize the impacts of water on the stability of the slopes in the Three Gorges Reservoir Region of Yangtze River, China.     

Kinematics and 3-D internal deformation of granular slopes: Analogue models and natural landslides

This study uses results from a series of analogue models, and field observations, scanned data and sections of natural landslides to investigate the kinematics and internal deformation during the failure of an unstable slope. The models simulate collapse of granular slopes and focus on the spatial and temporal distribution of their internal structures. Using a series of systematically designed models, we have studied the effect of friction and deformability of the runout base on internal deformation within a granular slope. The results of these different models show that the collapse of granular slopes resulted in different-generation extensional faults at the back of the slope, and contractional structures (overturned folds, sheath folds and thrusts) at the toe of the slope. The failure surfaces and the volume of the failure mass changed both spatially and temporally. Younger failure surfaces formed in the back of the older ones by incorporating additional new material from the head of the slope. Our model results also show that the nature of the runout base has a significant influence on the runout distance, topography and internal deformation of a granular slope. Model results are compared with natural landslides where local profiles were dug in order to decipher the internal structures of the failure mass. The natural cases show similar structural distribution at the head and toe of the failure mass. As in model results, our field observations indicate the presence of at least two generations of failure surfaces where the older ones are steeper.     

Rainfall-triggered large landslides on 15 December 2005 in Van Canh District, Binh Dinh Province, Vietnam

Landslides are one of the most dangerous hazards in Vietnam. Most landslides occur at excavated slopes, and natural slope failures are rare in the country. However, the volume of natural slope failures can be very significant and can badly affect large areas. After a long period of heavy rainfall in the fourth quarter of 2005 in Van Canh district, a series of landslides with volumes of 20,000–195,000 m³ occurred on 15 December 2005. The travel distances for the landslides reached over 300–400 m, and the landslides caused some remarkable loud booming noises. The failures took place on natural slopes with unfavorable geological settings and slope angles of 28–31°. The rainfall in the fourth quarter of 2005 is estimated to have a return period of 100 years and was the main triggering factor. Because of the large affected area and low population density, resettling people from the dangerous landslide-prone residential areas to safer sites was the most appropriate solution. In order to do so, a map of landslide susceptibility was produced that took into account slope angle, distance to faults, and slope aspect. The map includes four levels from low to very high susceptibility to landslides.     

Landslide characterization using active and passive seismic imaging techniques: a case study from Kerala,India

The unusually intense precipitations of the 2018 monsoon triggered numerous landslides in the Western Ghats region, southwest of India. Although the landslides caused no casualties, significant damage to property and infrastructure was observed. We present, as a case study, the results of active and passive seismic prospecting at two of those landslides with the goal of characterizing them, in a first application of shallow seismic exploration to landslides in the region. Our deployments included both sites perturbed by the landslides and unperturbed slopes adjacent to them with the purpose of identifying possible structural differences between slopes that underwent landsliding from slopes that were not affected. We analyze seismic sections obtained using the multi-channel analysis of surface waves technique and compare the results with seismic noise analyzed using seismic interferometry. We show that different analyses give similar results. The lateral variations observed in the shear-wave velocity distribution below the different profiles are well correlated with dominant frequency determined from seismic noise horizontal-to-vertical spectral ratios. Our measurements were taken after the landslides occurred. In hindsight, our results suggest that soil thickness played a major role in the triggering of landslides.

     

湖北省清江流域滑坡分布规律与减灾对策研究

清江流域是湖北省滑坡高易发区,滑坡灾害频发,造成了较大的经济损失,危害大。该区地质环境复杂,地貌形态以中山为主,河谷深切,岸坡陡峭,构造发育,新构造运动表现为大面积间歇性上升运动; 区内共发育滑坡2843处,其中滑坡2275处,崩塌型滑坡568处,滑坡以小型为主,主要分布在人类工程活动比较频繁的地带。通过统计分析,清江流域滑坡的空间分布规律主要受控于地质环境条件和动力因素,动力因素包括自然动力因素和人为动力因素,前者以降雨为主,后者以切坡为主且日趋发展; 滑坡变形的时间规律主要表现为同发性、滞后性和不稳定的周期性; 滑坡的自身活动规律主要表现为继承性、隐蔽性、突发性和差异性; 针对性地提出了监测预警、搬迁避让、工程治理和地质环境保护等滑坡减灾对策。     

Rock mass classification and assessment of stability of critical slopes on national highway-22 in Himachal Pradesh

Rock slopes require geo-engineering evaluation to assess the instability of critical slopes leading to landslides particularly in Himalayan terrain where rocks are highly jointed, fractured and weathering prone. Interplay of discontinuities in the rocks coupled with other parameters is one of the prime causes of failure of slopes. Engineering rock mass classification, such as, rock mass rating (RMR) and slope mass rating (SMR) along with geological strength index (GSI) have widely been used for stability assessment of rock slopes above tunnel portals, and these classifications are employed here for assessment of stability of slopes of critical nature along Rampur-Powari highway in Himachal Pradesh. In the present study, out of 154 numbers of slopes, a total of 29 have been selected for assessment of their criticality by employing RMR, SMR and GSI.     

Structural and geomorphological aspects of the Kat landslides (Tokat—Turkey) and susceptibility mapping by means of GIS

Kat County, which is located in a slope of hilly region and constructed in the side of a mountain along the North Anatolian Fault Zone, is frequently subject to landslides. The slides occur during periods of heavy rainfall, and these events cause destruction to property, roads, agricultural lands and buildings. In the last few decades, a lot of houses and buildings have been damaged and destroyed. Settlement areas have remained evacuated for a long time. The slope instabilities in the study area are a complex landslide extending from north to south containing a lot of landslides. Field investigations, interpretation of aerial photography, analyses of geological data and laboratory tests suggest that some factors have acted together on the slopes to cause the sliding. In the wet season, the slopes became saturated. As the saturation of the earth material on the slope causesa rise in water pressure, the shear strength (resisting forces) decreases and the weight (driving forces) increases; thus, the net effect was to lower the safety factor. Previous failures have affected the rock mass, leading to the presence of already sheared surfaces at residual strengths. The relation between the joint planes and the instability of the slope in the study area was discussed and it was found that the potential slope instabilities are mainly in the directions of NW–SE, NE–SW and N–S. The landslide susceptibility map obtained by using the geographical information system showed that a large area is susceptible and prone to landslides in the northern part of the study area.An erratum to this article can be found at     

Large landslides triggered by caldera collapse events in Tenerife,Canary Islands

Landsliding is a significant process on volcanic edifices, with individual events exceeding several cubic kilometres in volume. The causes of such mass movements and their relationship with volcanic activity are still poorly understood. Landslide events are an important factor in the evolution of volcanic islands such as Tenerife, where vertical and lateral collapses have occurred repeatedly. Subaerial and submarine processes related to landslide events strongly influence the morphology of the island. On Tenerife there are three very big valleys, Güimar, La Orotava and Icod, that have been created by large landslide events with ages ranging from Upper Pliocene to Middle Pleistocene. The landslides affect the northern flanks of the island and the slopes of a large central volcanic edifice, the Las Canadas volcano, which is truncated by the Las Canadas caldera, a multicyclic collapse depression, formed between 1.02 and 0.17 Ma. We have focused our studies on the potential for caldera collapse events to trigger large scale landslides. The available geological and morphological information has been incorporated into numerical models, which simulate the destabilising effects of a caldera collapse episode. The results of the numerical modelling indicate that processes associated with caldera collapse events can overcome the stabilising forces on the volcano flank and trigger landslides. We propose that caldera collapse events may have triggered large landslides on the slopes of the Las Canadas volcano.     

Analysis of the 2003 Varunawat Landslide,Uttarkashi, India using Earth Observation data

Mass movements such as landslides in mountainous terrains are natural degradation processes and one of the most important landscape-building factors. Varunawat Parbat overlooking Uttarkashi town witnessed a series of landslides on 23 September 2003 and the debris slides and rock falls continued for 2 weeks. This landslide complex was triggered due to the incessant rainfall prior to the event, and its occurrence led to the blockage of the pilgrim route to Gangotri (source of the Ganges river) and evacuation of thousands of people to safer places. Though there was no loss of lives due to timely evacuation, heavy losses to the property were reported. High-resolution stereoscopic earth observation data were acquired after the incidence to study the landslide in detail with emphasis on the cause of the landslide and mode of failure. Areas along the road and below the Varunawat foothill region are mapped for landslide risk. It was found that the foothill region of the Varunawat Parbat was highly disturbed by man-made activities and houses are dangerously located below steep slopes. The potential zones for landslides along with the existing active and old landslides are mapped. These areas are critical and their treatment with priority is required in order to minimise further landslide occurrences.     

Dynamic features and effects of rainfall on landslides in the Three Gorges Reservoir region, China: using the Xintan landslide and the large Huangya landslide as the examples

The study area is located in Three Gorges Reservoir region, China. Over 200 landslides have been monitored over a number of years with their behavior being compared to the effective rainfall database for the study area. Analysis of the available data indicates that the occurrences of landslides in this region are controlled by rainfall, whose intensity and rainfall processes are the most important dynamic factors in determining the stability of slopes. Therefore, the relationship between rainfall and the movement of typical landslides has been specifically analyzed for the Xintan landslides and the large Huangya landslide by using the loading/unloading response ratio parameter of rainfall. The result of this study indicates that the mutation of the loading/unloading response ratio of rainfall of the Xintan landslide and the large Huangya landslide in the Three Gorges Reservoir region, China occurred just before their destabilization, which shows that the loading/unloading response ratio of rainfall and its changing feature can be taken as a precursor for the landslides induced by rainfall.     

Controlling factors of loess landslides in western China

Based on detailed field data from recent geo-hazards surveys in the Loess Plateau region of western China, this study analyzes the key factors that control loess landslides. The evolution phase of river valleys, the geological structure of slopes and the geometry of slopes are all found to play a role in determining the occurrence, distribution and other characteristics of loess landslides. Groundwater and vegetation also contribute to their formation. A combination of human engineering activities and precipitation events are the principal triggering factors for the instability of loess slopes.     

Earthquake-induced landslides in Central America

Central America is a region of high seismic activity and the impact of destructive earthquakes is often aggravated by the triggering of landslides. Data are presented for earthquake-triggered landslides in the region and their characteristics are compared with global relationships between the area of landsliding and earthquake magnitude. We find that the areas affected by landslides are similar to other parts of the world but in certain parts of Central America, the numbers of slides are disproportionate for the size of the earthquakes. We also find that there are important differences between the characteristics of landslides in different parts of the Central American isthmus, soil falls and slides in steep slopes in volcanic soils predominate in Guatemala and El Salvador, whereas extensive translational slides in lateritic soils on large slopes are the principal hazard in Costa Rica and Panama. Methods for assessing landslide hazards, considering both rainfall and earthquakes as triggering mechanisms, developed in Costa Rica appear not to be suitable for direct application in the northern countries of the isthmus, for which modified approaches are required.     

A multi-method approach for the characterization of landslides in an intramontane basin in the Andes (Loja,Ecuador)

In the last several decades, population growth in the cities of the Andes has caused urban areas to expand into landslide-prone areas. Fatal landslides affecting urban settlements are especially frequent in cities located in the Neogene intramontane basins of the Andes. These basins have similar situations and include geographical and geological features that frequently generate ground instabilities. We studied the characteristics of the mass movements observed in these basins by carrying out a detailed analysis of four landslides that have occurred in the Loja Basin (Ecuador). This multi-method study integrated geophysical, geotechnical methods, mineralogical studies and analyses of precipitation time series. Our study characterizes the slope movements as active, slow-moving, complex earthslide earthflows. According to Differential GPS measurements, these landslides move at velocities of up to several metres per year. Electrical resistivity tomography profiles show that most of the landslides are mainly surficial. Time-series analyses of precipitation reveal that rainfall events that are not exceptionally intensive can reactivate these landslides. This characteristic and the development of these landslides on low-gradient slopes are explained using the results obtained from the geotechnical and mineralogical analyses. We find that the smectite clay minerals detected in the mobilized geological formations, combined with the tropical climate of the northern Andean region, induce the observed weak slope stability conditions. The conceptual model for the studied landslides may aid in assessing landslide-prone areas in Loja and other Neogene intramontane basins of the Andes and can help to mitigate the associated risks.