Geological characteristics of landslides triggered by the 2016 Kumamoto earthquake in Mt. Aso volcano,Japan

On 16 April 2016, a M_w 7.0 earthquake occurred in Kumamoto city, Japan. The main shock induced two large landslides, namely the Aso Bridge landslide and the Aso Volcanological Laboratory landslide. Their topographical and geological conditions and motion features were investigated by using an unmanned aerial vehicle (UAV) and portable dynamic cone penetration tests (PPTs). The Aso Bridge landslide lies between elevations of 385 m and 725 m, with a total estimated volume of about 1,980,000 m³. The main body is composed of cohesive soil with lapilli and block. The Aso Volcanological Laboratory landslide lies on a slope between 483 m to 582 m, and the total volume is about 81,000 m³, with an average thickness of 4.5 m. The main body is composed of Kusasenrigahama volcanic pumice tephra beds. The material compositions and deposits of both landslides have low cohesion and easily induced shear failure for the two landslides. The sliding distance of the Aso Bridge landslide was long, the sliding direction almost unchanged from the scarp to the toe, and the sliding speed was rapid. The sliding distance of the Aso Volcanological Laboratory landslide, however, was short, the sliding direction changed from the N-direction at the scarp to the NW-direction at the toe, and the sliding speed was slow.

     

The genetic mechanism of a translational landslide

Translational landslides are common in China, particularly in the interbedded mudstone sandstone sequence of the Three Gorges reservoir area and the Sichuan basin. The paper discusses the genetic mechanism and limit equilibrium criterion for single and multi-translational landslides based on physical model tests and numerical analysis. It focuses particularly on the generation of hydrostatic pressure and uplift pressure under intense rainfall conditions and the corresponding deformation and failure processes. A model was constructed based on the actual conditions at the 17 million m³ Fengdian Kualiangdzi landslide and the 25 million m³ Tiantai village landslide. It revealed a clear relationship between the critical water head value and the dip angle of the sliding plane.      

Spatial distribution and failure mechanism of water-induced landslides in the reservoir areas of Southwest China

Water-induced landslides in hydropower reservoirs pose a great threat to both project operation and human life. This paper examines three large reservoirs in Sichuan Province, China. Field surveys, site monitoring data analyses and numerical simulations are used to analyze the spatial distribution and failure mechanisms of water-induced landslides in reservoir areas. First, the general rules of landslide development in the reservoir area are summarized. The first rule is that most of the landslides have rear edge elevations of 100–500 m above the normal water level of the reservoir, with volumes in the range of 10⁶–10⁷ m³. When the volume exceeds a certain amount, the number of sites at which the landscape can withstand landslides is greatly reduced. Landslide hazards mainly occur in the middle section of the reservoir and less in the annex of the dam site and the latter half of the reservoir area. The second rule is that sedimentary rocks such as sandstone are more prone to landslide hazards than other lithologies. Then, the failure mechanism of changes in the water level that reduces the stability of the slope composed of different geomaterials is analyzed by a proposed slope stability framework that considers displacement and is discussed with the monitoring results. Permeability is an essential parameter for understanding the diametrically opposed deformation behavior of landslides experiencing filling-drawdown cycles during operation. This study seeks to provide inspiration to subsequent researchers, as well as guidance to technicians, on landslide prevention and control in reservoir areas.     

A method for quick assessment of earthquake-triggered landslide hazards: a case study of the Mw6.1 2014 Ludian,China earthquake

Rapid assessment of the distribution of earthquake-triggered landslides is an important component of effective disaster mitigation. The effort should be based on both seismic landslide susceptibility and the ground shaking intensity, which is usually measured by peak ground acceleration (PGA). In this paper, we address this issue by analyzing data from the Mw6.1 2014 Ludian, China earthquake. The Newmark method of rigid-block modeling was applied to calculate the critical acceleration of slopes in the study area, which serve as measurement of slope stability under seismic load. The assessment of earthquake-triggered landslide hazard was conducted by comparing these critical accelerations with the distribution of known PGA values. The study area was classified into zones of five levels of landslide hazard: high, moderate high, moderate, light, and very light. Comparison shows that the resulting landslide hazard zones agree with the actual distribution of earthquake-triggered landslides. Nearly 70% of landslides are located in areas of high and moderately high hazard, which occupy only 17% of the study region. This paper demonstrates that using PGA, combined with the analysis of seismic landslide susceptibility, allows a reliable assessment of earthquake-triggered landslides hazards. This easy-operation mapping method is expected to be helpful in emergency preparedness planning, as well as in seismic landslide hazard zoning.

     

GIS-based landslide hazard zonation: a case study from the Parwanoo area,Lesser and Outer Himalaya,H.P., India

GIS-based landslide hazard zonation has been carried out for a tectonically active region of the Himalayas, which is under pressure for rapid economic development. Thematic layers of slope, fault, geology, land use, flow accumulation, drainage and roads were prepared based on topographic maps, satellite imagery, published geological maps and ground truth. Five classes of landslide hazard were identified; 24% of the total area falls into the Very high or High hazard zones where 54% of the observed landslides were recorded.      

A coupled slope cutting—a prolonged rainfall-induced loess landslide: a 17 October 2011 case study

Continuous and heavy precipitation in the early September 2011 triggered several landslides in Xi’ an, Shaanxi province, China. A particularly relevant example is the Bailu tableland landslide occurrence on 17 September 17 2011, which was responsible for 32 casualties. This was selected as a case study for investigating the trigger factors, formation process, and hazard characteristics of the landslides of this type. The results showed that: (1) The Bailu landslide possessed a relative height = 90 m and width = 170 m, respectively, an average initiation thickness was 10 m, a sliding direction and distance of 55° and 150 m, respectively, a total volume of 15 × 10⁴ m³, and an average deposit thickness of 12 m; (2)The main trigger factors were excessive slope cutting with a heavy and long duration of rainfall; (3) The landslide was a typical example of its type, based on the trigger factors since the formation process of the landslide is generally as follows: cutting leads to gravitational and stress field redistribution, initiating the appearance of cracks, which then enlarge after the continuous infiltration of rainwater. This results in the formation of additional cracks, and finally, slope failure; a nd (4) Based on our analyses of this landslide and previous events, we proposed equations to determine the critical precipitation threshold and the potential risk distance. This study provided an important reference for understanding and studying the mechanisms of this type of landslide, as well as guidelines for future disaster prevention and mitigation in this region.     

Mapping the susceptibility of rainfall and earthquake triggered landslides along China–Nepal highways

The 2015 Gorkha earthquake (Mw?=?7.8) caused significant earthquake triggered landslides (ETL) in a landscape that is heavily intervened by rainfall triggered landslides (RTL). China’s Belt and Road Initiative plan to boost South-Asian regional trade and mobility through two key highway corridors, i.e. 1) Longmu–Rasuwa–Kathmandu (LRK) and 2) Nyalam–Tatopani–Kathmandu (NTK) route, that dissect the Himalayas through this geologically unstable region. To understand the spatial characteristics and susceptibility of these ETL and RTL, we delineate the landslides by means of time variant satellite imageries, assess their spatial distribution and model their susceptibilities along the highway slopes. We use a coupled frequency ratio (FR) – analytical hierarchy process (AHP) model by considering nine landslide determinants, e.g. geomorphic type (slope, aspect, curvature, elevation), hydrologic type (erosive potential of gullies, i.e. stream power index and distance to streams), normalized difference vegetation index, lithology and civil structure type (i.e. distance to roads). The results demonstrate that elevation and slope predominantly control both these landslide occurrences. The model predicts locations of ETL with higher accuracy than RTL. On comparison, NTK was safer with 133.5 km² of high RTL or ETL (or both) landslide susceptible areas, whereas LRK has 216.04 km². For mapping the extent of these landslides, we constricted it to the slope units of highways to reduce the computational effort, but this technique successfully achieved an acceptable threefold average model prediction rate of 82.75% in ETL and 77.9% in RTL. These landslide susceptibility maps and route comparisons would provide guidance towards further planning, monitoring, and implementing landslide risk mitigation measures for the governments.

     

Reliability of landslide isopleth maps

  Following very heavy rainfall on 19/20 July 1983, 109 landslides occurred in the east of Findikli, Rize, north-east Turkey. The movements took place in completely weathered andesitic, dacitic and granitic rocks as well as slope debris. They extended over an area of approximately 25 km². The paper discusses the contour (isopleth) map prepared using data from the 1983 landslides and discusses its value for landslide hazard zoning. It is concluded that on the basis of 12 years of field evidence, a contour map derived from a precise inventory map can be a useful tool. Received: 28 November 1998 · Accepted: 15 May 1999     

Volcanic mountain area disaster caused by the Iwate–Miyagi Nairiku Earthquake of 2008, Japan

We conducted an investigation of the geotechnical damage caused by an earthquake that struck on June 14, 2008. The earthquake was of magnitude 7.2 and hit a volcanic mountain area in Northern Japan. During the earthquake, the largest strong motion ever, over 4G, was recorded at the ground surface in the source region. As a result of the earthquake, a landslide of 1.5 million m³ was generated near the top of the mountain and became a mud flow, traveling about 10 km downstream. The geomorphic characteristics of the mud flow are reported in this paper. Another huge landslide was generated upstream near the Aratosawa Dam. It was about 1 km in length, about 700 m in width and had a sliding mass volume of about 67 million m³, which slipped about 320 m. The geological features, the time series of the slide and the cause of the slide are also discussed. In addition, more than 50 landslide dams, formed due to the collapsed soil and rock, appeared after the earthquake. In this paper, the geotechnical properties of all the damage are introduced.     

Landslide hazard zonation of the Khorshrostam area, Iran

 Landslide hazard zonation is a method to evaluate the risk where there is the potential for landslides. The factors contributing to the hazard in an area can usually be identified, results of the investigations frequently being presented as a landslide hazard zonation map indicating zones of similar risk of the occurrence of a landslide. Korshrostam is one of the areas most susceptible to landslides in Iran with more than 13% of its surface being affected by landslide activity. The effects include damage or disturbance to villages, farmlands and roads as well as the exacerbation of erosion of the land surface and consequently an increase in the rate of sedimentation in the water flowing into the reservoir of the Manjil dam. The method of landslide zonation used in this study was based on a simple grid unit. A number of factors contributing to the likelihood of landsliding were considered, including lithology, slope, tectonic activity, land use and groundwater. For each grid unit, the incidence of landsliding and an assessment of the likely contributory factors were recorded in terms of a surface percentage index (SPI). A computer program was written using fuzzy sets to calculate the hazard potential index (HPI) for each unit. This was used to prepare the landslide hazard zonation map. Received: 10 June 1999 · Accepted: 16 September 1999     

Analysis of landslide stability under seismic action and subsequent rainfall: a case study on the Ganjiazhai giant landslide along the Zhaotong-Qiaojia road during the 2014 Ludian earthquake,Yunnan, China

In a strong earthquake, not only a large number of coseismic landslides are triggered, but relaxation and cracks in the rocks and soils are induced, which make these rocks and soils vulnerable to instability during subsequent rainfall; thus, strong earthquakes always have long-term effects on landslides. The geo-hazards along the Zhaotong-Qiaojia road in the 2014 Ludian earthquake (Ms 6.5) of Yunnan Province, China, were investigated, and the Ganjiazhai giant landslide was chosen as a case study. First, using the limit equilibrium analysis and Newmark method, the critical seismic intensity of the landslide before the earthquake was evaluated. Secondly, the dynamic failure process of the landslide under the measured ground motion was simulated with the discontinuous deformation analysis method. Lastly, based on stress–seepage coupling analysis and precipitation data from Ludian meteorological station, the stability of the landslide during subsequent rainfall after the earthquake was predicted. The results show that the critical seismic intensity was within degrees VIII–IX, which is consistent with the results of the earthquake damage investigation. The dynamic failure process can be divided into four stages, and four scarps formed; the potential sliding zones during the subsequent rainfall were at the first scarp and the fourth scarp, and their critical rainfall amounts were 35–40 mm and 55–60 mm, respectively. In this paper, failure process simulation and stability prediction of the landslide before, during, and after the strong earthquake are presented, which provide analysis methods for the dynamic stability of landslides in the meizoseismal area.

     

Landslide-susceptibility mapping in a semi-arid mountain environment: an example from the southern slopes of Sierra Nevada (Granada,Spain)

Landslide susceptibility is analysed in a semi-arid mountain environment, on the southern slope of Sierra Nevada. In a study area of 460 km², 252 landslides were inventoried, affecting 3.2% of the total surface area. These landslides were mainly slides and flows on phyllite, schist and marble units in the Inner Zone of the Betic Cordillera. The most relevant determining factors proved to be elevation, slope angle, slope aspect and lithology. Triggering factors include mainly short-term landslide generation during heavy rainfall, as well as sporadic earthquakes or long-term activation by land-use changes, river over-excavation, etc. Although landslide susceptibility, assessed by the GIS matrix method, is predominantly low, some 15% of the study area shows moderate to very high susceptibility, coinciding with the sites of public works in the region. The map drawn was validated by the degree-of-fit method, registering values above 83.2% for the zones of high and very high susceptibility.     

Engineering geology maps: landslides and geographical information systems

IAEG Commission No. 1—Engineering Geological Maps—is developing a guide to hazard maps. Scientists from 17 countries have participated. This paper is one of a series that presents the results of that work. It provides a general review of GIS landslide mapping techniques and basic concepts of landslide mapping. Three groups of maps are considered: maps of spatial incidence of landslides, maps of spatial–temporal incidence and forecasting of landslides and maps of assessment of the consequences of landslides. With the current era of powerful microcomputers and widespread use of GIS packages, large numbers of papers on the subject are becoming available, frequently founded on different basic concepts. In order to achieve a better understanding and comparison, the concepts proposed by Varnes (Landslide hazard zonation: a review of principles and practice, 1984) and Fell (Some landslide risk zoning schemes in use in Eastern Australua and their application 1992; Landslide risk assessment and acceptable risk. Can Geotech J 31:261–272, 1994) are taken as references. It is hoped this will also add to the international usefulness of these maps as tools for landslide prevention and mitigation. Six hundred and sixty one papers and books related to the topic are included in the references, many of which are reviewed in the text. This report is being continually updated and further references can be seen on the IAEG website () under Commission No. 1.     

基于ArcGIS的四川松新黑水河地区滑坡危险性评价

以松新黑水河地区作为研究区域,基于遥感解译、野外调查统计、地质环境分析、典型滑坡研究的基础上,选取坡度、工程地质岩组、斜坡结构、断裂构造、降雨、人类工程活动等6个与滑坡发生相关的要素作为危险性评价因子。在ArcGIS空间分析模块中,采用自然断点法的数据分类方法,运用频率比——面域模型,对研究区滑坡危险性进行了评价与区划。研究结果表明:松新黑水河地区滑坡危险性分区为:高危险区、中等危险区、低危险区3个区域,所占研究区面积比例分别为32%、50%、18%。     

High-resolution lidar-based landslide hazard mapping and modeling,UCSF Parnassus Campus,San Francisco,USA

Airborne lidar (light detection and ranging) was used to create a high-resolution digital elevation model (DEM) and produce landslide hazard maps of the University of California, San Francisco Parnassus Campus. The lidar DEM consisted of nearly 2.8 million interpolated elevation values covering approximately100 ha and posted on an 0.6 m horizontal grid, from which a set of 16 maps was produced. The first subset of maps showed aspects of the topography useful for landslide mapping, an engineering geological map and a qualitative slope hazard map. The second subset consisted of physics-based probabilistic landslide hazard maps for wet static, wet seismic, and dry seismic conditions. This case history illustrates the utility of lidar-based products, supplemented by field-based geological observations and physics-based probabilistic slope stability modeling, for the evaluation of existing and potential slope stability hazards on a steep and heavily forested site.      

The 17 February 2006 rock slide-debris avalanche at Guinsaugon Philippines: a synthesis

The paper presents a synthesis of the key findings of the conference and workshop convened to consider the causes of and lessons to be learned from the disastrous rockslide-debris avalanche on 17 February 2006 in southern Leyte, Philippines. Some 1,221 people died and the barangay of Guinsagon was buried. The geology, historical seismicity, progressive disintegration of the rock mass, development of smectite layers and the continuous development and movement of shears within the Philippine Fault Zone combine in the steep rugged terrain to produce massive landslides, of which the 15 million m³ Guinsaugon event was the latest. The relevance of recent heavy rain and an almost synchronous seismic event are considered but it is concluded that the movement was the result of progressive failures and tectonic weakening while the landslide hazard was increased by the presence of rice paddy fields in the valley bottom. An anecdotal time to failure curve is presented, based on eyewitness accounts and observations of instability. Attention is drawn to the importance of both the education and training of the local people in the recognition of signs of potential movement and a reporting management system. Such simple measures could save lives and empower local communities to take some ownership of their level of landslide risk.     

A new method for quantitative identification of potential landslide

A growing number of slope hazard and engineering case studies have shown that only one safety factor (SF) can predict landslide occurrence, but cannot identify potentially dangerous landslides, which is the major source of the most destructive landslides. To solve the problem, a safety factor of cohesion (SF_c) is proposed, and an improved slope stability analysis based on two safety factors is presented. Taking a sloping rock mass as a case study, the results showed that when SF_c was less than 1 and the ratio of the cohesive force to the sliding resistance force drops to less than 100%, the slope became a potential landslide. The study suggests a new method for quantitative identification of potential landslides and provides a more reliable safety evaluation index, thus can solve the difficulty of adjustment of potential landslides and provide a more reliable safety evaluation index for engineering.     

Earthquake-triggered landslides by the 1718 Tongwei earthquake in Gansu Province,northwest China

The 1718 great Tongwei earthquake in northwest China caused more than 300 large-scale landslides near the epicenter resulting in more than 70,000 deaths. Although previous studies agree that the earthquake-induced landslides in the area are loess-landslides, which slid along ancient terrain surfaces, there is a dearth of evidence to unravel the actual failure mechanisms of these widely-documented events. To clarify their characteristics and mechanisms, the landslides in Pan’an Town, located in Gansu Province, China were rigorously investigated. The field surveys revealed that the landslides occurred in an area comprising loess deposits of several tens of meters underlain by a basal mudstone layer. It was also revealed that instability in the area is strongly influenced by a river valley with large erosion bank slopes, as well as steep mudstone slopes, which are well developed. The majority of the landslides triggered by the Tongwei earthquake were loess-mudstone composite landslides, with the sliding surface in the deep mudstone. Three huge landslides on the northern mountain located at the river bend of Pan’an Town with a total volume of about 6.06 × 10⁸ m³ are the main mass movements during the 1718 catastrophe. In addition, by taking the typical landslide named the Weijiawan landslide as a case study, the internal structure of the earthquake-triggered landslides and their stability were studied. The new findings not only aided the unraveling of the failure mechanisms but also provided insights and knowledge on early recognition of earthquake-triggered landslides in northwest China towns, especially in the surrounding valley, which shares similar geological conditions with landslides studied in this paper.     

Evaluating landslide deposits along the Tsurukawa fault zone, Japan, using magnetic susceptibility

 This paper describes the results of in-situ measurements of magnetic susceptibility in landslide deposits along the Tsurukawa fault zone in central Japan. The measured magnetic susceptibility values range from 0.4 to 9.6×10^–3 (in SI) and correspond to the proportions of the two component materials, weathered volcanic ash and faulted rock fragments. The study shows that landslide deposits along the Tsurukawa fault zone are composed of varying proportions of weathered volcanic ash. The results contrast with some general assumptions concerning landslides along fault zones in Japan. Received: 16 April 1999 · Accepted: 10 August 1999     

Application of GIS-based statistical modeling for landslide susceptibility mapping in the city of Azazga,Northern Algeria

Landslide susceptibility mapping is a necessary tool in order to manage the landslides hazard and improve the risk mitigation. In this research, we validate and compare the landslide susceptibility maps (LSMs) produced by applying four geographic information system (GIS)-based statistical approaches including frequency ratio (FR), statistical index (SI), weights of evidence (WoE), and logistic regression (LR) for the urban area of Azazga. For this purpose, firstly, a landslide inventory map was prepared from aerial photographs and high-resolution satellite imagery interpretation, and detailed fieldwork. Seventy percent of the mapped landslides were selected for landslide susceptibility modeling, and the remaining (30%) were used for model validation. Secondly, ten landslide factors including the slope, aspect, altitude, land use, lithology, precipitation, distance to drainage, distance to faults, distance to lineaments, and distance to roads have been derived from high-resolution Alsat 2A satellite images, aerial photographs, geological map, DEM, and rainfall database. Thirdly, we established LSMs by evaluating the relationships between the detected landslide locations and the ten landslides factors using FR, SI, LR, and WoE models in GIS. Finally, the obtained LSMs of the four models have been validated using the receiver operating characteristics curves (ROCs). The validation process indicated that the FR method provided more accurate prediction (78.4%) in generating LSMs than the SI (78.1%),WoE (73.5%), and LR (72.1%) models. The results revealed also that all the used statistical models provided good accuracy in landslide susceptibility mapping.