Factors Controlling Seismic Susceptibility of the Sele Valley Slopes: The Case of the 1980 Irpinia Earthquake Re-Examined

Most of the documented slope failures triggered by the 1980 Irpinia earthquake (M_s 6.9) occurred in the upper Sele valley epicentral area (southern Italy). The early investigations revealed some puzzling characteristics of the slope failure distribution, i.e., (i) the higher landslide concentration on the valley slopes located farther away from the earthquake fault; (ii) the predominance of re-activations over first-time movements. The analyses of factors controlling the landslide concentrations indicates that the differences in hydrological setting and in slope were the two main causal factors whereas the seismic shaking, according to the radiation pattern modelling, could have been characterised by a relatively low rate of decrease across the valley. The aspect of the slopes did not play a significant role. The differences in groundwater conditions between the western and eastern valley sides were probably enhanced by the earthquake. In addition to the probable pore-water pressure rise, the seismic shaking caused large increases in the flow of springs draining the western aquifer, and this made the adjacent flysch slopes more prone to landsliding. Data from the available literature suggest that the effects of earthquake-induced groundwater release on seismic landslide distribution is especially important for normal-fault events. The Sele valley case also indicates that the slope of the pre-existing landslides is an important factor controlling their susceptibility to seismic re-activations.     

Origin and palaeo‐environments of calcareous sediments in the Moshaweng dry valley,southeast Botswana

Quaternary sedimentation in the Moshaweng dry valley of southeastern Botswana is evaluated on the basis of geomorphological evolution and sedimentological analyses. Stratigraphic evidence reveals an upper surface (1095 m) containing abundant sil‐calcrete, an intermediate surface (1085 m) in which sil‐calcrete underlies nodular calcrete and lower (1075 m) surface in which sil‐calcrete and nodular calcrete are interbedded. This subdivision is reflected in the geochemical composition of the sediments which show an overall trend of decreasing SiO₂ content (and increasing CaCO₃ content) with depth from the highest to the lowest surface levels. The calcretes and sil‐calcretes represent modifications of pre‐existing detrital Kalahari Group sand and basal Kalahari pebbles which thinned over a Karoo bedrock high. Modification took place during wet periods when abundant Ca⁺⁺‐rich groundwater flowed along the structurally aligned valley system. With the onset of drier conditions, water table fluctuations led to the precipitation of nodular calcretes in the phreatic layer to a depth of about 20 m. A major geochemical change resulted in the preferential silicification of the nodular calcrete deposits. Conditions for silica mobilization may be related to drying‐induced salinity and in situ geochemical differentiation brought about by pebble dissociation towards the top of the sediment pile. As calcretization and valley formation progressed to lower levels, silica release took place on a diminishing scale. Thermoluminescence dating infers a mid‐Pleistocene age for sil‐calcrete formation suggesting that valley evolution and original calcrete precipitation are much older. Late stage dissolution of CaCO₃ from pre‐existing surface calcretes or sil‐calcretes led to the formation of pedogenic case‐hardened deposits during a time of reduced flow through the Moshaweng system possibly during the upper or late Pleistocene. Copyright © 2002 John Wiley & Sons, Ltd.     

东亚夏季风强弱年物理量的逐候变化及其对松嫩流域降水的影响

用施能定义的东亚夏季风指数,分别找出典型夏季风强弱年1961和1980年,分析水平风速、假相当位温、高度等的逐候变化特征与盛夏季节松嫩流域逐候降水量的关系。分析表明:东亚夏季风强弱对松嫩流域盛夏降水量有显著影响。在强夏季风年,较大的南风、较高的假相当位温、较深的东亚大槽使降水持续偏多。同时还发现,无论夏季风强弱,假相当位温高值总是与多降水相联系。     

云南干热河谷特色农业开发

云南是一个山原省份，河谷盆地是农业发展的最适宜地区，由于部份河谷盆地存在干热气候，坡在退化，生态环境恶化等自然障碍，以及受农业基础设施薄弱的制约，使得传统农业明显欠发达；同时干热河谷地区又具有光热与土地等自然资源优势条件，适宜发展特色作农业和反季节农业。在农业产业结构调整优化的发展形势下，需要开展区域特色农业建设以实现农业开发效益的提高和农业生态环境的改善，提出具体的分区开发方向和相关产业化措施。     

金沙江干热河谷土地荒漠化评价的植被指标分析

土地荒漠化是在人和自然因素的综合作用下，地表环境退化的总过程，其实质是土地减弱或丧失生长绿色植物的能力。因此，植被因子是评价土地荒漠化的关键因子。植被盖度和生物量能很好地反映土地是否荒漠化和荒漠化的强弱程度，但靠常规方法要获得这两项指标非常困难。以元谋老城乡为试验区，对土地荒漠化与植被盖度和生物量的关系、利用遥感技术获取的植被指数与植被盖度和生物量的关系进行了分析研究。试验研究表明，植被指数与盖度和生物量具有很高的相关性，是对二者的综合反映；植被指数为土地荒漠化评价提供了定量依据。     

流域水土资源信息系统的构建

该文分析基于GIS、RS和地学模型集成的流域水土资源信息系统的开发背景、目标 ,结合实际系统的开发 ,提出了系统开发的思路和技术路线 ,并探讨系统开发的方向和实际应用的可能性。     

西藏帕隆藏布河谷崩塌滑坡、泥石流的分布规律

西藏帕隆藏布河谷崩塌滑坡、泥石流灾害严重。崩塌滑坡、泥石流的分布 ,因谷坡坡向的水热条件差异而导致坡向差异 ,因地貌发育和形态的沿程分异显现沿程差异 ,因其促发条件的差异又显现灾种差异。采用有序样品最优分割和方差分析等定量方法 ,揭示了崩塌滑坡、泥石流的差异性分布规律 :全河段可分为上游峡谷泥石流密集段 ,中游宽谷泥石流及崩塌滑坡较密集段 ,和下游、拉月曲峡谷崩塌滑坡、泥石流极密集段 ;北岸崩塌滑坡和泥石流比南岸数量多、规模大 ;崩塌滑坡有向下游增大增多之趋势。进而对道路平面选线原则提出了建议。     

A procedure for landslide susceptibility zonation by the conditional analysis method

Numerous methods have been proposed for landslide probability zonation of the landscape by means of a Geographic Information System (GIS). Among the multivariate methods, i.e. those methods which simultaneously take into account all the factors contributing to instability, the Conditional Analysis method applied to a subdivision of the territory into Unique Condition Units is particularly straightforward from a conceptual point of view and particularly suited to the use of a GIS. In fact, working on the principle that future landslides are more likely to occur under those conditions which led to past instability, landslide susceptibility is defined by computing the landslide density in correspondence with different combinations of instability factors. The conceptual simplicity of this method, however, does not necessarily imply that it is simple to implement, especially as it requires rather complex operations and a high number of GIS commands. Moreover, there is the possibility that, in order to achieve satisfactory results, the procedure has to be repeated a few times changing the factors or modifying the class subdivision. To solve this problem, we created a shell program which, by combining the shell commands, the GIS Geographical Research Analysis Support System (GRASS) commands and the gawk language commands, carries out the whole procedure automatically. This makes the construction of a Landslide Susceptibility Map easy and fast for large areas too, and even when a high spatial resolution is adopted, as shown by application of the procedure to the Parma River basin, in the Italian Northern Apennines.     

基于GIS的梁北煤矿底板突水危险性评价

我国有60％的煤矿不同程度地受到底板岩溶承压水的威胁,尤其是奥陶系和寒武系灰岩含水层水量大、水压高,已经发生多次重大突水事故。底板突水的控制因素很多,主要有矿山压力、含水层水压、隔水层阻水能力、原始导高、构造复杂程度等,本文以梁北煤矿突水为例,在分析矿井突水因素基础上,综合选取上述因素作为评价指标并定量化,利用ArcGIS平台,构建了底板突水危险性多因素评价模型。评价结果表明,该矿在现有疏水降压条件下,从2008年8月,矿井东部采区11111,11151,21031工作面由中等危险区转为安全区,疏水降压取得显著效果。研究表明,GIS可在矿井防治水工作中发挥重要作用。     

泸定县孙家沟泥石流成因及防治对策探讨

泸定县孙家沟位于泸定县城后山,是一条典型的泥石流沟,对泸定县城居民、交通及房屋等造成严重威胁。通过实地考察,分析了孙家沟泥石流的成因,并提出了防治对策建议。