Mapping areas of potential slope failures in cohesive soils using a shadow-casting algorithm – A case study from SW Sweden

When performing landslide susceptibility mapping of rotational slides in fine grained soils, slope algorithms found in common GIS software have two major shortcomings. Firstly, these types of terrain algorithms only consider the slope angle at the surface. Secondly, the algorithm is local by its design i.e. it only considers neighbouring pixels. Due to the behaviour of a retrogressive rotational landslide, it would be more preferable to consider slope information as a predetermined cross-section angle from the base of the slope. This paper presents a new method using shadow casting algorithms for preliminary landslide susceptibility mapping in cohesive soils. A case study from western Sweden is also presented.     

斜坡地震稳定性研究的若干问题

地震滑坡是由于地震的触发作用而导致接近或恰好处于临界状态的坡体发生提前滑动的地质事件。2022年9月5日,四川省甘孜藏族自治州泸定县发生6.8级地震,诱发了大量滑坡,造成严重的人员伤亡和财产损失。本文采用野外调查和遥感解译相结合的方法对泸定地震极震区内的地震滑坡进行解译,并基于ArcGIS地理信息系统平台分析了高程、坡度、坡向、曲率、地层岩性、与断层距离、地震峰值加速度、与水系距离和与道路距离等9个因子与地震滑坡的空间分布规律。通过引入受试者工作特征曲线(ROC)来改进层次分析法(AHP),克服了AHP方法采用专家打分确定影响因子权重的主观性,并采用改进的AHP方法对泸定地震滑坡易发性进行了评估。结果表明,泸定地震在极震区内共诱发5008处滑坡,总面积达17.28 km²。高程、与水系距离和与道路距离是诱发泸定地震滑坡的主控因素。地震滑坡的极高易发区和高易发区面积约占研究区总面积的26%,主要分布在大渡河河谷两岸。采用ROC曲线下面积(AUC)对评估结果进行检验,AUC值为0.8505,表明评估模型具有较高的准确性。本研究可为地震滑坡易发性评估方法的改进提供参考,并为泸定地震灾后重建规划提供科学支撑。

     

青海湖南岸黑马河黄土剖面碳酸盐含量与记录的古气候变化

在青海湖南岸黑马河2.2 m厚的黄土剖面中,以5 cm的间隔采样,进行了碳酸盐、碳酸盐中Sr含量以及磁化率的测定,通过对比分析研究了12.7 ka以来青海湖湖区古气候的变化,结果表明碳酸盐、碳酸盐中Sr含量、磁化率等基本较真实的记录了该区自12.7 kaBP以来经历的多次暖湿—干冷古气候变化过程。     

中国大陆科学钻探（CCSD）主孔100-2000m区间磁化率的变异特征及其地质意义

对中国大陆科学钻探主孔100—2000m区间岩心样品磁化率与钻孔原位测井磁化率进行系统时比研究。结果表明,控制岩石磁化率的主要因素是岩性和退变质作用,其中蛇纹石化石榴石橄榄岩的磁化率最大,样品平均磁化率为86．277×10-3SI,正片麻岩,退变质榴辉岩,榴辉岩,副片麻岩次之,角闪岩的磁化率最小,样品平均磁化率为1．698×10-3SI。不同退变质程度榴辉岩的磁化率特征具有明显的差异:中-强程度退变质榴辉岩由于退变质过程所产生的磁铁矿和钛铁矿-钛磁铁矿,其磁化率最大;随着退变质作用的进一步加剧,这些磁铁矿和钛铁矿-钛磁铁矿被完全分解,导致完全退变质榴辉岩的磁化率最小;新鲜榴辉岩的磁化率介于两者之间。在该深度区间,约70％岩心样品磁化率与测井磁化率的比值小于4．0,其中以<2．0为主,相同岩性岩石(如榴辉岩,退变质榴辉岩和副片麻岩)磁化率的比值随深度变化较小。岩心样品磁化率和测井磁化率之间的欧氏距离位于3．0-6．4范围,且随深度变化不明显,如在100～600m和1500～2000m两个深度范围的欧氏距离分别为3．0-5．2和3．2～5．3,表现出相似的变化特征,显示了在此区间深度范围内,地层压力对磁化率的基本没有影响。     

GIS-based weights-of-evidence modelling of rainfall-induced landslides in small catchments for landslide susceptibility mapping

Landslide susceptibility mapping is a vital tool for disaster management and planning development activities in mountainous terrains of tropical and subtropical environments. In this paper, the weights-of-evidence modelling was applied, within a geographical information system (GIS), to derive landslide susceptibility map of two small catchments of Shikoku, Japan. The objective of this paper is to evaluate the importance of weights-of-evidence modelling in the generation of landslide susceptibility maps in relatively small catchments having an area less than 4 sq km. For the study area in Moriyuki and Monnyu catchments, northeast Shikoku Island in west Japan, a data set was generated at scale 1:5,000. Relevant thematic maps representing various factors (e.g. slope, aspect, relief, flow accumulation, soil depth, soil type, land use and distance to road) that are related to landslide activity were generated using field data and GIS techniques. Both catchments have homogeneous geology and only consist of Cretaceous granitic rock. Thus, bedrock geology was not considered in data layering during GIS analysis. Success rates were also estimated to evaluate the accuracy of landslide susceptibility maps and the weights-of-evidence modelling was found useful in landslide susceptibility mapping of small catchments.     

河南西南部典型白垩纪剖面的岩石磁组构特征及其构造意义

对河南西南部西峡盆地阳城-丹水上白垩统岩石磁学、磁组构的研究表明,该陆相沉积地层磁性矿物以及特征剩磁载体以赤铁矿为主,并含少量磁铁矿,且磁铁矿与赤铁矿相对含量比例随剖面由老到新显示出逐渐增加的趋势。岩石磁组构主要受顺磁性矿物以及反铁磁性矿物的控制。全剖面磁化率椭球结果显示在原生沉积组构基础上叠加了最早期阶段的弱变形组构;同时,全剖面以及各岩石地层单元磁化率椭球体主轴方向的变化揭示了两个不同方向及大小的构造挤压作用导致磁化率最大轴从NNW-SSE向转至NW-SE向,后又到NNW-SSE向的变化模式,一方面是由于华南、华北板块NE-SW向的构造挤压导致;另一方面是由两板块构造挤压而引起的桐柏-大别造山带上地壳物质相对下地壳发生东向构造逃逸和挤出过程中与东部块体物质间发生的挤压作用引起,这两种不同的挤压应力作用在盆地发展的不同阶段各占主要地位。     

青藏高原西北缘晚新生代沉积岩古流向的磁化率各向异性确定及其构造意义

古流向的确定是重建沉积物来源及沉积过程的有效方法,而磁化率各向异性作为古流向恢复的可靠信息载体在室内沉积实验和具体工作中已得到认可.本文对青藏高原西北缘柯克亚剖面晚新生代地层鸟恰群、阿图什组和西域组80块样品开展了磁组构研究,磁面理与磁线理图、磁化率各向异性度与磁化率椭球体形状因子图直观地说明研究对象均具有磁面理较磁线理发育的特点,代表了原生沉积组构特征.柯克亚剖面乌恰群、阿图什组和西域组的磁化率各向异性测量则恢复了三个时期的古流向.古流向在不同时期的变迁显示了重要的青藏高原西北缘的隆升信息.乌恰群与阿图什组、阿图什组与西域组之间的古流向的改变反映出西昆仑山北缘具有西早东晚的构造隆升过程.     

滑坡风险评价的理论与方法研究

作为防灾减灾的重要措施之一,滑坡风险评价已经成为近年来国际上滑坡研究的热点,并形成了较为完备的滑坡风险管理体系。国内的滑坡风险研究则起步较晚,滑坡风险评价的关键支撑技术体系尚未建立。本文对滑坡风险评价中的关键理论和方法进行梳理,阐述了国际滑坡风险评价的理论框架和技术流程,介绍了国内外滑坡易发性、危险性和风险评价的最新进展,评述了滑坡易发性评价、扩展范围预测、频率分析以及承灾体易损性评价的主要方法,阐明了现阶段滑坡风险评价的重点领域和前沿科学问题,并对滑坡灾害的风险评价提出了三点展望。     

The use of the anisotropy of magnetic remanence in the resolution of the anisotropy of magnetic susceptibility into its ferromagnetic and paramagnetic components

The anisotropy of magnetic susceptibility (AMS) is often controlled by both ferromagnetic (sensu lato) and paramagnetic minerals. The anisotropy of magnetic remanence (AMR) is solely controlled by ferromagnetic minerals. Jelínek (Trav. Geophys. 37 (1993)) introduced a tensor derived from the isothermal AMR whose normalized form equals the normalized susceptibility tensor provided that the ferromagnetic fraction is represented by multi-domain magnetite. The present paper shows the close correlation between these tensors for a collection of strongly magnetic specimens containing multi-domain magnetite. In addition, acceptable correlation between the tensors was also found for a collection of specimens containing single-domain magnetite. A new method is developed for the AMS resolution into ferromagnetic and paramagnetic components using the AMR. Some examples are presented of this resolution in mafic microgranular enclaves in granodiorite and in gneisses of the KTB borehole.