Landslide hazard zonation mapping and comparative analysis of hazard zonation maps

Landslide hazard zonation mapping at regional level of a large area provides a broad trend of landslide potential zones. A macro level landslide hazard zonation for a small area may provide a better insight into the landslide hazards. The main objective of the present work was to carry out macro landslide hazard zonation mapping on 1：50,000 scale in an area where regional level zonation mapping was conducted earlier. In the previous work the regional landslide hazard zonation maps of Srinagar- Rudraprayag area of Garhwal Himalaya in the state of Uttarakhand were prepared using subjective and objective approaches. In the present work the landslide hazard zonation mapping at macro level was carried out in a small area using a Landslide Hazard Evaluation Factor rating scheme. The hazard zonation map produced by using this technique classifies the area into relative hazard classes in which the high hazard zones well correspond with high frequency of landslides. The results of this map when compared with the regional zonation maps prepared earlier show that application of the present technique identified more details of the hazard zones, which are broadly shown in the earlier zonation maps.     

Landslide hazard zonation mapping in ghat road section of Kolli hills,India

Landslides are the most common natural disaster in hilly terrain which causes changes in landscape and damage to life and property. The main objective of the present study was to carry out landslide hazard zonation mapping on 1：50,000 scale along ghat road section of Kolli hills using a Landslide Hazard Evaluation Factor（LHEF） rating scheme. The landslide hazard zonation map has been prepared by overlaying the terrain evaluation maps with facet map of the study area. The terrain evaluation maps include lithology, structure, slope morphometry, relative relief, land use and land cover and hydrogeological condition. The LHEF rating scheme and the Total Estimated Hazard（TEHD） were calculated as per the Bureau of Indian Standard（BIS） guidelines（IS： 14496（Part-2） 1998） for the purpose of preparation of Landslide Hazard Zonation（LHZ） map in mountainous terrains. The correction due to triggering factors such as seismicity, rainfall and anthropogenic activities were also incorporated with Total Estimated Hazard to get final corrected TEHD. The landslide hazard zonation map was classified as the high, moderate and low hazard zones along the ghat road section based on corrected TEHD.     

暴雨过程中不同尺度运动性质演化的比较

通过设计合适的滤波器,对2001年9月18-20日华西暴雨过程中气象探测资料进行滤波处理,提取大、中尺度运动信息.在此基础上,通过对不同尺度运动信息的诊断分析,研究暴雨过程的不同阶段大、中尺度大气运动非平衡性质的演化及其对暴雨的影响,结果表明:在暴雨发生的不同阶段,大、中尺度运动的非平衡性质变化是不一样的,中尺度非平衡强迫对暴雨落区有重要影响.     

Large scale mass movements triggered by the Kashmir earthquake 2005, Pakistan

The SPOT image analysis in Muzaffarabad Azad Kashmir,northwest Himalayas,Pakistan reveals that the Kashmir earthquake 2005 triggered a number of coseismic mass movements along the hanging wall block of the Muzaffarabad Fault.The Neelidandi and Langarpura rock falls have been identified as two major reactivated mass movements with an estimated volume of 3.1 × 106m3and 5.76 × 106m3,respectively.The Neelidandi and Langarpura mass movements were initiated during earthquake in the direction of northwest-southeast extension and northeastsouthwest directed thrusting,respectively.The Neelidandi rock fall occurred in sheared cherty dolomites and limestones of the Cambrian Muzaffarabad Formation,whereas the Langarpura rock fall occurred in alternating clays,shales,claystones,siltstones and sandstones of the Miocene Murree Formation.These rock units along the fault are highly fractured and jointed.The geotechnical maps and geological longitudinal profiles show the relationship between the geometrical characteristics and mechanism of these mass movements.Their characteristics were analyzed according to the role of topographic,seismic,geological and tectonic factors.The steep topography,sheared rocks,lithology,coseismic uplift and strong ground shaking of the hanging wall block along Muzaffarabad Fault facilitated the gravity collapse of these mass movements.     

Landslide mapping and analysis along the China-Pakistan Karakoram Highway based on SBAS-InSAR detection in 2017

The Karakoram Highway(KKH), a part of the China–Pakistan Economic Corridor(CPEC), is a major highway connecting northern Pakistan to China. The inventorying and analysis of landslides along KKH are challenging because of poor accessibility, vast study area, limited availability of ground-based datasets, and the complexity of landslide processes in the region. In order to preserve life, property, and infrastructure, and to enable the uninterrupted and efficient operation of the KKH, it is essential to strengthen measures for the prevention and control of geological disasters. In the present study, SBASInSAR(Small Baseline Subsets-Interferometric Synthetic Aperture Radar) was used to process 150 scenes of Sentinel 1-A images in the year 2017 along the Karakoram Highway. A total of 762 landslides, including 57 complex landslides, 126 rock falls, 167 debris slides, and 412 unstable slopes, ranging in size between 0.0017 and 10.63 km2 were identified. Moreover, this study also gains an inventory of 40 active glacier movements in this region. Landslide categorization, displacements characteristics, spatial distribution, and their relationship with various contributing factors have been successfully investigated along the entire KKH using image interpretation and frequency-area statistics. The criteria adopted for landslides categorization is presented in the study. The results showed that the 2-D ground deformation derived in Hunza valley echoes well with the general regional landslides characteristics. The spatial distribution analysis revealed that there are clumped distributions of landslides in the Gaizi, Tashkurgan, and Khunjerab in China, as well as in Hunza valley, and north of Chilas city in Pakistan. Statistical results indicated that these landslides mainly occur on south-facing slopes with a slope angle of 20°– 45° and elevation relief of 550 – 2,100 m. Landslide development is also related to low vegetation cover and weathering effects in mountain gullies. Overall, our study provides scientific data support and theoretical references for prevention, control, and mitigation of geological disasters in the Karakoram region.     

Landslide susceptibility assessment of the region affected by the 25 April 2015 Gorkha earthquake of Nepal

Nepal was hit by a 7.8 magnitude earthquake on 25^th April, 2015. The main shock and many large aftershocks generated a large number of coseismic landslips in central Nepal. We have developed a landslide susceptibility map of the affected region based on the coseismic landslides collected from remotely sensed data and fieldwork, using bivariate statistical model with different landslide causative factors. From the investigation, it is observed that most of the coseismic landslides are independent of previous landslides. Out of 3,716 mapped landslides, we used 80% of them to develop a susceptibility map and the remaining 20% were taken for validating the model. A total of 11 different landslide-influencing parameters were considered. These include slope gradient, slope aspect, plan curvature, elevation, relative relief, Peak Ground Acceleration (PGA), distance from epicenters of the mainshock and major aftershocks, lithology, distance of the landslide from the fault, fold, and drainage line. The success rate of 87.66% and the prediction rate of 86.87% indicate that the model is in good agreement between the developed susceptibility map and the existing landslides data. PGA, lithology, slope angle and elevation have played a major role in triggering the coseismic mass movements. This susceptibility map can be used for relocating the people in the affected regions as well as for future land development.     

Landslide susceptibility mapping using Genetic Algorithm for the Rule Set Production (GARP) model

Investigation on landslide phenomenon is necessary for understanding and delineating the landslide prone and safer places for different land use practices. On this basis, a new model known as genetic algorithm for the rule set production was applied in order to assess its efficacy to obtain a better result and a more precise landslide susceptibility map in Klijanerestagh area of Iran. This study considered twelve landslide conditioning factors (LCF) like altitude, slope, aspect, plan curvature, profile curvature, topographic wetness index (TWI), distance from rivers, faults, and roads, land use/cover, and lithology. For modeling purpose, the Genetic Algorithm for the Rule Set Production (GARP) algorithm was applied in order to produce the landslide susceptibility map. Finally, to evaluate the efficacy of the GARP model, receiver operating characteristics curve as well as the Kappa index were employed. Based on these indices, the GARP model predicted the probability of future landslide incidences with the area under the receiver operating characteristics curve (AUC-ROC) values of 0.932, and 0.907 for training and validating datasets, respectively. In addition, Kappa values for the training and validating datasets were computed as 0.775, and 0.716, respectively. Thus, it can be concluded that the GARP algorithm can be a new but effective method for generating landslide susceptibility maps (LSMs). Furthermore, higher contribution of the lithology, distance from roads, and distance from faults was observed, while lower contribution was attributed to soil, profile curvature, and TWI factors. The introduced methodology in this paper can be suggested for other areas with similar topographical and hydrogeological characteristics for land use planning and reducing the landslide damages.     

Landslide hazard and community-based risk reduction effort in Karanganyar and the surrounding area, central Java, Indonesia

Karanganyar and the surrounding area are situated in a dynamic volcanic arc region, where landslide frequently occurs during the rainy season. The rain-induced landslide disasters have been resulting in 65 fatalities and a substantial socioeconomical loss in last December 2007. Again, in early February 2009, 6 more people died, hundreds of people temporary evacuated and tens of houses damaged due to the rain-induced landslide. Accordingly, inter-disciplinary approach for geological, geotechnical and social investigations were undertaken with the goal for improving community resilience in the landslide vulnerable villages. Landslide hazard mapping and community-based landslide mitigation were conducted to reduce the risk of landslides. The hazard mapping was carried out based on the susceptibility assessment with respect to the conditions of slope inclination, types and engineering properties of lithology/soil as well as the types of landuse. All of those parameters were analyzed by applying weighing and scoring system which were calculated by semi qualitative approach (Analytical Hierarchical Process). It was found that the weathered andesitic-steep slope (steeper than 30o) was identified as the highest susceptible slope for rapid landslide, whilst the gentle colluvial slope with inter-stratification of tuffaceous clay-silt was found to be the susceptible slope for creeping. Finally, a programme for landslide risk reduction and control were developed with special emphasize on community-based landslide mitigation and early warning system. It should be highlighted that the social approach needs to be properly addressed in order to guarantee the effectiveness of landslide risk reduction.     

Co-seismic landslide inventory and susceptibility mapping in the 2008 Wenchuan earthquake disaster area, China

The Ms 8.0 May 12,2008 Wenchuan earthquake triggered tens of thousands of landslides.The widespread landslides have caused serious casualties and property losses,and posed a great threat to post-earthquake reconstruction.A spatial database,inventoried 43,842 landslides with a total area of 632 km 2,was developed by interpretation of multi-resolution remote sensing images.The landslides can be classified into three categories:swallow,disrupted slides and falls;deep-seated slides and falls,and rock avalanches.The correlation between landslides distribution and the influencing parameters including distance from co-seismic fault,lithology,slope gradient,elevation,peak ground acceleration(PGA) and distance from drainage were analyzed.The distance from co-seismic fault was the most significant parameter followed by slope gradient and PGA was the least significant one.A logistic regression model combined with bivariate statistical analysis(BSA) was adopted for landslide susceptibility mapping.The study area was classified into five categories of landslide susceptibility:very low,low,medium,high and very high.92.0% of the study area belongs to low and very low categories with corresponding 9.0% of the total inventoried landslides.Medium susceptible zones make up 4.2% of the area with 17.7% of the total landslides.The rest of the area was classified into high and very high categories,which makes up 3.9% of the area with corresponding 73.3% of the total landslides.Although the susceptibility map can reveal the likelihood of future landslides and debris flows,and it is helpful for the rebuilding process and future zoning issues.     

INTERDECADAL SEA LEVEL VARIATION AT THE JAPANESE COAST AND LARGE SCALE CLIMATE STATE

Thirty years of monthly mean anomalies of sea level(SL) at 15 Japanese coastal stations, sea sur-face temperature (SST) and sea level pressure (SLP) in or over the northern Pacific were analyzed bycanonical correlation analysis (CCA) to study the relationship between the interdecadal SL variationand large scale climate state. Given two time-varying fields this technique identifies the pair ofspacial patterns with optimally correlated time series.The results show that there are two important air-sea interactive processes in the extratropicalPacific region for the variation of the SL at the Japanese coast on interdecadal scale. One is theocean heating or cooling of the atmosphere over the Kuroshio extension region, which results in ahuge SLP anomalous vortex with planetary spacial scale big enough to change the global climate. An-other is the large Kuroshio meander phenomenon controlled by the large-scale wind-stress curls oneyear earlier in the adjacent region of the Hawaiian Islands. The first process im     

Seismic damage of mountain tunnels during the 5.12 Wenchuan earthquake

A number of mountain tunnels suffered significant damage to various extent during the 2008 Wenchuan earthquake in China. Damage ranging from small to heavy cracking was observed both at the portal and inside the tunnels, while some sections close to the faults completely collapsed. A summary of qualitative data collected from reports and papers is presented regarding the behavior of the 55 mountain tunnels near the epicenter during the earthquake. Based on the seismic investigation and data collection of mountain tunnels, the tunnel damage is classified into six most common damage models involving cracking, spalling, shear failure, dislocation, pavement uplift and collapse. Detailed study and discussion are then carried out on the damage models. In order to examine the influencing factors of the damage magnitude of the mountain tunnels, the correlations between epicentral distance, earthquake intensity, overburden depth, geological condition and damage levels are analyzed. The relationships between earthquake parameters and different damage models are developed and discussed. Also, suggestions are provided to improve the seismic resistance of mountain tunnels.     

Slope Instability on Pyroclastic Deposits： Landslide Distribution and Risk Mapping in Zacapoaxtla, Sierra Norte De Puebla, Mexico

Introduction The impact produced by landsliding in diverse regions of the world has given rise to the development and implementation of different methods, techniques and tools to understand the mechanisms of movements involved, as well as to create maps o…     

Landslide susceptibility: a statistically-based assessment on a depositional pyroclastic ramp

This study aimed to produce a high-quality landslide susceptibility map for Teziutlán municipality, a landslide-prone region in Mexico, which is characterised by a depositional pyroclastic ramp. The heterogeneous quality of available topographic information(i.e. higher resolution digital elevation model only for a sub-region) encouraged to confront modelling results based on two different study area delineations and two raster resolutions. Input data was based on the larger modelling region L15(163 km2) and smaller S(70 km2; located inside L15) with an associated raster cell size of 15 m(region L15 and S15) and 5 m(region S5). The resulting three data sets(L15, S15 and S5) were included into three differently flexible modelling techniques(Generalized Linear Model-GLM, General Additive Model-GAM, Support Vector Machine-SVM) to produce nine landslide susceptibility models. Preceding variable selection was performed heuristically and supported by an exploratory data analysis. The final models were based on the explanatory variables slope angle, slope aspect, lithology, relative slope position, elevation, convergence index, distance to streams, distance to springs and topographic wetness index. The ability of the models to classify independent test data was elaborated using a k-fold cross validation procedure and the AUROC(Area Under the Receiver Operating Characteristic) metric. In general, all produced landslide susceptibility maps depicted the hillslopes of the ravines, which cut the pyroclastic ramp, as prone to landsliding. The modelling results showed that predictive performances(i.e. AUROC values) slightly increased with an increasing flexibility of the applied modelling technique. Thus, SVM performed best, while the GAM outperformed the GLM. This tendency was most distinctive when modelling with the largest landslide sample size(i.e. data set L15; n = 662 landslides). Non-linear classifiers(GAMs, SVMs) performed slightly better when trained on the basis of lower raster resolution(data set S15) compared to the 5 m counterparts(data set S5). Highest predictive performance was obtained for the model based on data set L15 and the SVM classifier(median AUROC: 0.82). However, SVMs also indicated the highest degree of model overfitting. This study indicates that the decision to delineate a study area, the selection of a raster resolution as well as the chosen classification technique can affect varying aspects of subsequent modelling results. The results do not support the assumption that a higher raster resolution(i.e. a more detailed digital representation of the terrain) inevitably leads to better performing or geomorphically more plausible landslide susceptibility maps.     

Seismic response of the Lengzhuguan slope during Kangding Ms5.8 earthquake

In order to investigate the role of the amplification of peak ground acceleration(PGA) in seismic landslide formation mechanisms and study how earthquake waves interact with rock structures, a few strong-motion seismometers are installed at various locations on both sides of the Lengzhuguan gully. Five strong-motion seismometers were triggered at different depths in a tunnel at the same altitude during the Kangding Ms 5.8 earthquake on November 25 th, 2014. The data reveal that the horizontal peak acceleration(PGA_H) at each site decreased with increasing site depths. The PGAH at the deepest monitoring site(99 m from the tunnel entrance) was approximately half that of the outermost site. The amplitude of the acceleration response spectrum was also attenuated from the entrance inwards, the dynamic magnification factor(β) of the standard acceleration spectrum was less than 3.5, and rate of change was the same as that for the amplitude acceleration response. The Fourier spectra of each monitoring site also decreased from the outside inwards, and the components of the Fourier spectra were more complex at the surface.     

Integrated rockfall hazard and risk assessment along highways: An example for Jiuzhaigou area after the 2017 Ms 7.0 Jiuzhaigou earthquake,China

This work addresses the integrated assessment of rockfall(including landslides) hazards and risk for S301, Z120, and Z128 highways, which are important transportation corridors to the world heritage site Jiuzhai Valley National Park in Sichuan, China. The highways are severely threatened by rockfalls or landslide events after the 2017 Ms 7.0 Jiuzhaigou earthquake. Field survey(September 14-18 th, 2017, May 15-20 th, 2018, and September 9-17 th, 2018), unmanned aerial vehicle(UAV), and satellite image identified high-relief rockfalls and road construction rockfalls or landslides along the highway. Rockfall hazard is qualitatively evaluated using block count, velocity, and flying height through a 3D rockfall simulation at local and regional scales. Rockfall risk is quantitatively assessed with rockfall event probability, propagation probability, spatial probability, and vulnerability for different block volume classes. Approximately 21.5%, 20.5%, and 5.3% of the road mileage was found to be subject to an unacceptable(UA) risk class for vehicles along S301, Z120, and Z128 highways, respectively. Approximately 20.1% and 3.3% of the road mileage belong to the UA risk class for tourists along Z120 and Z128 highways, respectively. Results highlighted that high-relief rockfall events were intensively located at K50 to K55(Guanmenzi to Ganheba) and K70 to K72(Jiudaoguai to Shangsizhai Village) road mileages along S301 highway and KZ18 to KZ22(Five Flower Lake to Arrow Bamboo Lake) road mileages, KZ30(Swan Lake to Virgin Forests), and KY10.5 kilometers in Jiuzhai Valley. Rockfalls in these locations were classified under the UA risk class and medium to very high hazard index. Road construction rockfalls were located at K67(Jiuzhai Paradise) and K75–K76 kilometers along S301 highway and KZ12 to KZ14(Rhino Lake to Nuorilang Waterfall), KZ16.5 to KZ17.5(Golden Bell Lake), KY5(Lower Seasonal Lake), and KY14(Upper Seasonal Lake) kilometers along Z120 and Z128 highway in Jiuzhai Valley. Rockfalls in these areas were within a reasonable practicable risk to UA risk class and very low to medium hazard index. Finally, defensive measures, including flexible nets, concrete walls, and artificial tunnels, could be selected appropriately on the basis of the rockfall hazard index and risk class. This study revealed the integration between qualitative rockfall hazard assessment and quantitative rockfall risk assessment, which is crucial in studying rockfall prevention and mitigation.     

Landslide susceptibility mapping using an integrated model of information value method and logistic regression in the Bailongjiang watershed,Gansu Province,China

Bailongjiang watershed in southern Gansu province, China, is one of the most landslide-prone regions in China, characterized by very high frequency of landslide occurrence. In order to predict the landslide occurrence, a comprehensive map of landslide susceptibility is required which may be significantly helpful in reducing loss of property and human life. In this study, an integrated model of information value method and logistic regression is proposed by using their merits at maximum and overcoming their weaknesses, which may enhance precision and accuracy of landslide susceptibility assessment. A detailed and reliable landslide inventory with 1587 landslides was prepared and randomly divided into two groups, (i) training dataset and (ii) testing dataset. Eight distinct landslide conditioning factors including lithology, slope gradient, aspect, elevation, distance to drainages, distance to faults, distance to roads and vegetation coverage were selected for landslide susceptibility mapping. The produced landslide susceptibility maps were validated by the success rate and prediction rate curves. The validation results show that the success rate and the prediction rate of the integrated model are 81.7 % and 84.6 %, respectively, which indicate that the proposed integrated method is reliable to produce an accurate landslide susceptibility map and the results may be used for landslides management and mitigation.     

Application of ultrasonic CT method in nondestructive detection of interior defects in large scale concrete structural member of bridge

The ultrasonic computed tomography (USCT) method is derived from the basic principles of X-ray section scanning. This method records the arriving times of ultrasonic wave between the probes and the sources to calculate the elastic wave velocity values in the section using the arrival times. Through analyzed the distribution of elastic wave velocity in aim area, the information of the strength and the homogeneity of the investigated zone could be got indirectly. The authors introduced the operational principle of USCT and a practical case of using this method to detect the interior defects in large scale concrete structural member. Compared with other exploration methods, this method is more efficient and accurate.     

Application of ultrasonic CT method in nondestructive detection of interior defects in large scale concrete structural member of bridge

The ultrasonic computed tomography （USCT） method is derived from the basic principles of X-ray section scanning. This method records the arriving times of ultrasonic wave between the probes and the sources to ealculate the elastic wave velocity values in the section using the arrival times. Through analyzed the distribution Of elastic wave velocity in aim area, the information of the strength and the homogeneity of the investigated zone could be got indirectly. The authors introduced the operational principle of USCT and a practical case of using this method to detect the interior defects in large scale concrete structural member. Compared with other exploration methods, this method is more efficient and accurate.     

On the winter circulation of the northern South China Sea and its relation to the large scale oceanic current

The nonwind-driven mechanism of the winter circulation in the northern South China Sea is discussed. Linked by the Bashi Strait to the Pacific Ocean, the northern South Cnina Sea is treated as a part of the Pacific western boundary where the circulation variation (except the very thin surface layer) is closely related to that of the ocean interior and the effect of local wind might be neglected (at least for some seasons). Based on the assumption that the thick and strong westward current which flows in through the Bashi Strait can effectively prevent water exchange between the northern and southern South China Seas, the model sea only includes the northern part. Barotropic numerical experiments show that part of this westward current is deflected by the continental slope and forms the slope area NE current—the South China Sea Warm Current. Besides, the topographical flow fed by the extension of the western boundary current and the anticyclonic eddy born near the eastern boundary are also fundamental components of the South China Sea Warm Current. The reflection of the incident Rossby waves by the continental slope is found to be of significance in the intensification of the South China Sea Warm Current. Contribution No. 1362 from Institute of Oceanology, Academia     

Seismic response of cracking features in Jubao Mountain during the aftershocks of Jiuzhaigou Ms7.0 earthquake

Jiuzhaigou is a world-heritage site located in the plateau area of Northwest Sichuan Province,China. Serious slope failures in the epicentral area were triggered by the Ms7.0 Jiuzhaigou earthquake occurred on August 8, 2017. The source areas of the hazards are usually concentrated near ridge crests,revealing the possible occurrence of ground motion amplification phenomena. To explore the role of the amplification of ground motions in the formation of earthquake-triggered slope failures, two seismometers were installed, on the next day after the main shock, at the bottom of the slope of Jubao Mountain near the seismogenic fault. The two monitoring sites are located at elevations of 1414 m(J1) and 1551 m(J2, the top of the mountain). Five aftershocks were recorded by the monitoringinstruments. We compared the mean levels of the peak ground acceleration(PGA) observed at different locations, and investigated the directional variations in the shaking energy by analyzing the polar diagrams of the Arias intensity(Ia). Then, in order to identify the directional resonance phenomenon and their frequencies and amplification coefficients, we examined the horizontal-to-vertical spectral ratio(HVSR) and the standard spectral ratio(SSR). Polar diagrams of the Arias intensity(Ia) indicated that the site response of Jubao Mountain showed a pronounced directivity(in the EW direction) with shaking maxima near the hill top oriented orthogonally to the elongation of the relief. We observed an obvious resonance phenomenon at site J2 at relatively low frequencies(2.5-9 Hz) and very weak spectral amplifications at site J1 at high frequencies(5-15 Hz), which suggested that the predominant frequency of monitoring site J2 was obviously attenuated and that the difference in the spectra was related to the influences of the local-scalesite conditions of the whole mountain. The results of spectral ratio analyses(HVSR and SSR) showed that the direction of resonance was concentrated around an EW orientation, and the amplification factors near the hill top were larger than 2. It suggests that geologic factors also play a significant role in the anisotropic amplifications affecting the tops of slopes besides the topographic effects.