A method for producing digital probabilistic seismic landslide hazard maps

The 1994 Northridge, California, earthquake is the first earthquake for which we have all of the data sets needed to conduct a rigorous regional analysis of seismic slope instability. These data sets include: (1) a comprehensive inventory of triggered landslides, (2) about 200 strong-motion records of the mainshock, (3) 1:24 000-scale geologic mapping of the region, (4) extensive data on engineering properties of geologic units, and (5) high-resolution digital elevation models of the topography. All of these data sets have been digitized and rasterized at 10 m grid spacing using ARC/INFO GIS software on a UNIX computer. Combining these data sets in a dynamic model based on Newmark's permanent-deformation (sliding-block) analysis yields estimates of coseismic landslide displacement in each grid cell from the Northridge earthquake. The modeled displacements are then compared with the digital inventory of landslides triggered by the Northridge earthquake to construct a probability curve relating predicted displacement to probability of failure. This probability function can be applied to predict and map the spatial variability in failure probability in any ground-shaking conditions of interest. We anticipate that this mapping procedure will be used to construct seismic landslide hazard maps that will assist in emergency preparedness planning and in making rational decisions regarding development and construction in areas susceptible to seismic slope failure.     

Seismic hazard analysis for the Philippines

Two sample probabilistic hazard maps for the Philippine Region are compiled. In these are shown various levels of expected horizontal ground acceleration for some given annual probability of exceedence, namely, for 0.1% a.p.e. and for 0.01% a.p.e. Such hazard maps are needed by structural engineers for compiling seismic zoning maps. The hazard maps are derived from source-zone or seismogenic maps, which, in turn, are compiled from seismographic, geologic, and geotectonic data. Much weight is put on geotectonic data rather than on seismographic data. The former lends support to extrapolating to much longer periods of exposure time or longer periods of recurrence.     

Interpretation of probability of landsliding triggered by rainfall

This paper is a contribution to an important aspect of the systematic and quantitative assessment of landslide hazard and risk. The focus is on site-specific and detailed assessment for rainfall-triggered landslides and, in particular, on the estimation and interpretation of the temporal probability of landsliding. Historical rainfall data over a 109-year period were analysed with particular reference to a site along the Unanderra and Moss Vale Railway Line in the State of New South Wales, Australia. It is shown that the recurrence interval of landsliding and hence annual probability of occurrence is subject to significant uncertainty and that it cannot be regarded as a constant. Accordingly landslide hazard varies spatially as well as being a function of time. For the example case study considered in this paper the annual probability of landslide occurrence was estimated to be in the range 0.026–0.172. However, the mean annual probability of landslide reactivation was estimated to be in the range 0.037–0.078. Utilisation of methods for probability assessment proposed in this paper will contribute to more realistic assessment of hazard and risk and, therefore, to more efficient risk management.     

Stochastic Modeling of Progressive Failure in Heterogeneous Soil Slope

Accurate and efficient simulation of the slope stability, certainly gives the reliable approach for the hazard preparedness. However, inherent difficulties associated with the slope failure make the situation very difficult. First, the computation of fracture path based on the strict mathematical formalism is cumbersome especially for the progressive failure phenomenon. Second, due to the lack of reliable knowledge on material properties, stochastic simulation is necessary. Stochastic modeling together with the progressive failure phenomenon is apparently difficult task. In this paper, heterogeneous slope is simulated considering the progressive failure phenomenon using the modified finite element method introducing the fracture along the edge of the meshes thus incorporating the time evolution of the fracture surface. This is achieved by restructuring the tessellation in every fracture stage. Unlike remeshing this technique only increases the number of total nodes while number of meshes remaining same, which is simple and natural. Further, in this research, effect of uncertainty in the material properties upon the uncertainty in the response of soil slope has been evaluated, hence giving the reliable probabilistic estimation of the factor of safety, failure surface and deformation of the slope. Thus the simulation based on the more reliable understanding of the material properties and the efficient numerical procedure for the progressive failure phenomenon can give the reliable result of the simulation for the heterogeneous soil slope thus enabling the more accurate way for hazard preparedness.     

云南新平2002-08-14特大滑坡泥石流灾害及防治对策

云南新平2002—08—14发生了超过百年一遇的特大滑坡泥石流灾害。这次灾害点多、面广，几乎同时暴发。通过对灾害的实地考察，分析了灾害发生的地质、气象、地貌等方面原因。崩塌滑坡灾害沿哀牢山东坡的高山与中低山交接处分布，而泥石流灾害则沿戛洒江和现刀河的支流沟口分布，这一区域处于红河大断裂范围内。灾害主要是特大暴雨激发所致。针对本区的社会条件和自然条件，提出了防灾、减灾对策，具体分为近期措施和远期措施。     

Debris flows in Glacier National Park, Montana: geomorphology and hazards

Debris flows are one of the many active slope-forming processes within Glacier National Park, Montana. Most debris flow landforms exhibit classic morphology with a distinct failure scarp, incised channel, channel levees, and toe deposits that often develop a lobate form. The Precambrian metasediments that dominate Glacier National Park's geology weather into angular clasts that range in size from platy gravels to boulders. Classic debris flows occur in areas where the topographic expression provides a debris source from cliff faces and an accumulation of regolith, often in the form of talus slopes. Many of these debris flows have long runout zones and can travel many hundreds of meters. Often they cross hiking trails or roads, including the main east–west highway, Going-to-the-Sun Road. Debris flows impacting the road have resulted in several near fatalities, and hikers have been forced to cross active debris flows to reach safe ground. The magnitude of debris flows varies between high magnitude channel incising events and low magnitude channel filling and/or reworking events. The frequency of debris flow events is irregular and appears to be controlled by the hydrology of triggering storms and antecedent moisture conditions, not by the debris supply. As a result, debris flow magnitude is not a function of frequency, but is more closely related to the characteristics of antecedent conditions and individual storms.     

泥石流防灾优先性研究

防灾优先性是减灾决策的组成部分，阐述了防灾优先性与减灾先性的关系及其在灾害评价中的地位和作用，提出了适合我国国情的泥石流防灾优先性评价模式和计算公式，并应用于四川阿坝州。研究成果可为各级政府和灾害管理部门制定泥石流减灾规划和防治政策提供科学基础和决策依据，亦可为其灾害类型的防灾优先性评价提供参考模式。     

对气象致灾因子危险度诊断方法的探讨

气象灾害损失与风险大小取决于气象致灾因子危险性、承灾体脆弱性、自然与人为防控在孕灾环境中时空配置格局及交互作用.但对于一定区域与时段而言,后两个因素相对稳定,气象致灾因子多变,其不同时空分布格局很大程度上决定了灾害的地域性及时间变化特征.对致灾因子危险性予以准确诊断是客观评估气象灾害损失与风险大小的基本前提.为此,文中提出了气象致灾因子危险度定义及点面相结合的诊断模型:(1)将危险度定义为事件致灾因子量值与风险阈值场中各级风险水平阈值之间的接近程度;(2)采用随机变量概率分布模型估计各地各种特定概率下的气象事件致灾因子量级,构建气象致灾因子风险阈值场;(3)联合空间相似和距离参量构建危险度诊断模型,以刻划事件致灾因子与各级风险阈值分布形态相似性及数值差异大小,据此计算事件致灾因子与风险阈值场中各级风险阈值的接近程度,以接近度最大为原则确定某过程致灾因子总体危险性水平等级.然后以上海地区风致灾因子危险性诊断为例,计算了上海各地不同风险水平下年最大风速阈值以及各地各级年最大风速的风险水平,构建了上海地区年最大风速的风险阈值场,结果表明:上海沿海地区的南汇、崇明、金山等地为年最大风速高值区,也是一定风险水平下的最大风速高值区,同时又是8级以上强风频发区及高危险区;相对地,本市较内陆的区域,则是年最大风速低值区,也是一定风险水平下的最大风速低值区,同时又是8级以上强风稀遇区及低危险区;一定重现期下最大风速阈值地区分布也有类似规律.最后,应用该模型对影响上海地区热带气旋及其他天气过程共30余个例作出风危险度诊断,结果表明,以1977年9月11日的7708号热带气旋风危险度最高,总体上与风险水平为8年一遇的年最大风速阈值最为接近;1986年8月27日8615号热带气旋与1983年6月3日其他天气过程个例风危险度为第2,总体接近于7年一遇年最大风速阈值;8114号与9711号热带气旋风危险度则与4年一遇年最大风速阈值最为接近;7413号、7503号、7909号、8506号热带气旋的风危险度接近3年一遇年最大风速阈值;而0509号热带气旋"麦莎"、0515号热带气旋"卡努"风危险度总体上接近于2年一遇的年最大风速阈值.其他热带气旋影响个例,其风危险度多数与重现期约2年一遇的年最大风速阈值接近.实际应用结果表明,所提出的这一点面结合的危险度的诊断方法,能较客观定量地评定气象致灾因子的危险性程度.     

Mapping global patterns of drought risk: An empirical framework based on sub-national estimates of hazard,exposure and vulnerability

A global map of drought risk has been elaborated at the sub-national administrative level. The motivation for this study is the observation that little research and no concerted efforts have been made at the global level to provide a consistent and equitable drought risk management framework for multiple regions, population groups and economic sectors. Drought risk is assessed for the period 2000–2014 and is based on the product of three independent determinants: hazard, exposure and vulnerability. Drought hazard is derived from a non-parametric analysis of historical precipitation deficits at the 0.5°; drought exposure is based on a non-parametric aggregation of gridded indicators of population and livestock densities, crop cover and water stress; and drought vulnerability is computed as the arithmetic composite of high level factors of social, economic and infrastructural indicators, collected at both the national and sub-national levels. The performance evaluation of the proposed models underlines their statistical robustness and emphasizes an empirical resemblance between the geographic patterns of potential drought impacts and previous results presented in the literature. Our findings support the idea that drought risk is driven by an exponential growth of regional exposure, while hazard and vulnerability exhibit a weaker relationship with the geographic distribution of risk values. Drought risk is lower for remote regions, such as tundras and tropical forests, and higher for populated areas and regions extensively exploited for crop production and livestock farming, such as South-Central Asia, Southeast of South America, Central Europe and Southeast of the United States. As climate change projections foresee an increase of drought frequency and intensity for these regions, then there is an aggravated risk for global food security and potential for civil conflict in the medium- to long-term. Since most agricultural regions show high infrastructural vulnerability to drought, then regional adaptation to climate change may begin through implementing and fostering the widespread use of irrigation and rainwater harvesting systems. In this context, reduction in drought risk may also benefit from diversifying regional economies on different sectors of activity and reducing the dependence of their GDP on agriculture.     

Why are flood and landslide victims less willing to take mitigation measures than the public?

Almost annually, natural hazards such as floods and landslides cause a great deal of financial loss and human suffering in Taiwan. In order to gain a better understanding of disaster preparedness, this paper examines several factors in relation to hazard mitigation behavior: social economic status (education, income), psychological vulnerability (sense of powerless and helpless), risk perception (perceived impact and control) and social trust. The statistical analysis reported here is based on the “2004 National Risk Perception Survey of Floods and Landslides in Taiwan”. The main findings include: (1) in comparison with general public, victims are less willing to adopt risk mitigation measures than the public, even though they perceive larger impacts, worry more about the hazard, and pay more attention to hazard information; (2) trust, risk perception and social economic status are positive predictors for mitigation intentions, whereas psychological vulnerability is a negative predictor; and (3) psychological variables are stronger predictors for mitigation intentions than that of socio-economic variables. In light of these findings, the policy implications and intervention strategy are also discussed.