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Many of the numerical techniques used for seismic zonation studies treat one-dimensional structural models and/or the incidence of plane polarized body waves. These techniques are often not adequate for laterally heterogeneous structures and for sources that are not located beneath the site of interest. In such cases a more rigorous treatment of the combined effects of the source, the path and the site response is needed. This can be accomplished with a hybrid approach combining modal summation and the finite-difference technique. To demonstrate the differences between these techniques, the ground motion in the city of Benevento (Italy) is modelled. We first compare the results obtained with one-and two-dimensional structural models for vertical incidence of plane polarized body waves. These results are then compared with those obtained with the hybrid approach for two-dimensional structural models.The comparisons have allowed us to find important differences in the response obtained with the different modelling techniques. For the same site, these differences consist of strong variations in amplitude and in the shape of the spectral amplifications. For a seismic source which is not located beneath the site, vertical incidence of waves significantly overestimates the local hazard in a laterally homogeneous structure. For a laterally heterogeneous area, we can conclude that one-dimensional modelling fails to estimate the seismic hazard, whereas for a seismic source which is not located beneath the site of interest, two-dimensional modelling with vertical incidence of plane polarized body waves may not allow reliable estimates to be made of the frequency bands at which amplifications occur. The results obtained for two-dimensional structural models are used for a zonation of the city of Benevento. 相似文献
124.
康古尔金矿地球化学分带模式及其预测标志 总被引:2,自引:1,他引:2
康古尔金矿受火山运动及韧性剪切作用双重控制;成矿母岩为中—酸性火山岩;矿化与黄铁绢英岩化、绿泥石化、硅化关系密切;指示元素组合类型,主要成矿元素Au和多金属为选择分布的两期成矿产物;矿床地球化学分带明显,但主要成矿元素相关性不明显,所建立的矿床剥蚀深度数学模式,对于矿脉勘探评价和寻找深部肓矿体具有一定的指导意义。 相似文献
125.
F. Gutiérrez-Santolalla M. Gutiérrez-Elorza C. Marín G. Desir C. Maldonado 《Environmental Geology》2005,48(3):360-369
A highly active collapse sinkhole field in the evaporitic mantled karst of the Ebro river valley is studied (NE Spain). The subsidence is controlled by a NW-SE trending joint system and accelerated by the discharge of waste water from a nearby industrial state. The morphometry, spatial distribution and temporal evolution of the sinkholes have been analysed. The volume of the sinkholes yields a minimum estimate of average lowering of the surface by collapse subsidence of 46 cm. The clustering of the sinkholes and the tendency to form elongated uvalas and linear belts, in a NW–SE direction have a predictive utility and allow the establishment of criteria for a hazard zonation. With the precipitation record supplied by a pluviograph and periodic cartographic and photographic surveys the influence of heavy rainfall events on the triggering of collapses has been studied. 相似文献
126.
An approach for GIS-based statistical landslide susceptibility zonation—with a case study in the Himalayas 总被引:14,自引:1,他引:14
Ashis K. Saha Ravi P. Gupta Irene Sarkar Manoj K. Arora Elmar Csaplovics 《Landslides》2005,2(1):61-69
Landslide susceptibility zonation (LSZ) is necessary for disaster management and planning development activities in mountainous regions. A number of methods, viz. landslide distribution, qualitative, statistical and distribution-free analyses have been used for the LSZ studies and they are again briefly reviewed here. In this work, two methods, the Information Value (InfoVal) and the Landslide Nominal Susceptibility Factor (LNSF) methods that are based on bivariate statistical analysis have been applied for LSZ mapping in a part of the Himalayas. Relevant thematic maps representing various factors (e.g., slope, aspect, relative relief, lithology, buffer zones along thrusts, faults and lineaments, drainage density and landcover) that are related to landslide activity, have been generated using remote sensing and GIS techniques. The LSZ derived from the LNSF method, has been compared with that produced from the InfoVal method and the result shows a more realistic LSZ map from the LNSF method which appears to conform to the heterogeneity of the terrain. 相似文献
127.
曲靖盆地地下水固有脆弱性评价 总被引:1,自引:0,他引:1
根据地下水在不同岩类中贮存形式、运移条件的不同及水动力特征的差异,曲靖盆地地下水分为孔隙水、裂隙水及岩溶水三大类型,盆地及其周缘有6个主要水文地质单元。采用美国EPA地下水脆弱性评价方法DRASTIC,根据水文地质实际调查及已有的曲靖盆地水文、地质等资料对该盆地地下水进行固有脆弱性评价。得出曲靖盆地地下水脆弱性主要为中等、较高;并圈出了地下水易于污染的高风险区。该结果对曲靖市的土地开发利用和城市规划有借鉴意义。 相似文献
128.
Carbonation of Cl-rich scapolite boudins in Skallen, East Antarctica: evidence for changing fluid condition in the continental crust 总被引:2,自引:0,他引:2
Spectacular reaction textures in poikiloblastic scapolitite boudins, within marbles in the continental crust exposed in the Lützow–Holm Complex, East Antarctica, provide insights into the changing fluid composition and movement of fluid along grain boundaries and fractures. Petrographic and geochemical features indicate scapolite formation under contrasting fluid compositions. Core composition of scapolite poikiloblasts (ScpI) are marialitic (Cl = 0.7 apfu) whereas rims in contact with biotite or clinopyroxene are meionite rich. Fine‐grained recrystallized equigranular scapolite (ScpII) shows prominent chemical zoning, with a marialitic core and a meionitic rim (Cl = 0.36 apfu). Scapolite poikiloblasts are traversed by ScpIII reaction zones along fractures with compositional gradients. Pure CO2 fluid inclusions are observed in healed fractures in scapolite poikiloblasts. These negative crystal‐shaped fluid inclusions are moderately dense, and are believed to be coeval with ScpIII formation at temperatures >600 °C and a minimum pressure of c. 3.8 kbar. Grain‐scale LA‐ICPMS studies on trace and rare earth elements on different textural types of scaplolites and a traverse through scapolite reaction zone with compositional gradient suggest a multistage fluid evolution history. ScpI developed in the presence of an internally buffered, brine‐rich fluid derived probably from an evaporite source during prograde to peak metamorphism. Recrystallization and grain size reduction occurred in the presence of an externally sourced carbonate (CaCO3)‐bearing fluid, resulting in the leaching of Cl, K, Rb and Ba from ScpI along fractures and grain boundaries. Movement of fluids was enhanced by micro‐fracturing during the transformation of ScpI to ScpIII. Fractures in fluorapatite are altered to chlorapatite proving evidence for the pathways of escaping Cl‐bearing fluids released from ScpI. The present study thus provides evidence for the usefulness of scapolite in fingerprinting changing volatile composition and trace element contents of fluids that percolate within the continental crust. 相似文献
129.
基于GIS的北京市延庆县地质灾害易发性区域划分 总被引:3,自引:0,他引:3
随着灾害科学研究的深入,区域地质灾害已成为其重要的研究领域。文章利用遥感技术及GPS工具获取地质灾害的特征信息,在对地质灾害的成因背景分析基础上,运用GIS空间分析功能和地质灾害危险性评价、评估理论构建了地质灾害发育度模型。以北京市延庆县为实验区,采用ArcEngine&.NET进行易发性分区程序的编写,计算研究区域内单元网格的发育度值。为了克服调查数据的局限性和人为因素,在计算发育度时引入修正系数,从延庆县DEM数据中提取单元格网内的地形坡度值,根据坡度值区间确定修正系数。将发育度计算结果按照一定规律、原则聚类。进行地质灾害易发性区域划分,取得了与实际情况较为一致的结果。基于“3S”技术及灾害地质条件,采用地质灾害发育度模型,可以较好地用于区域地质灾害易发性区域的划分,并能为防灾、减灾提供重要信息。 相似文献
130.
西北地区侏罗纪地质事件及其在地层划分对比中的意义 总被引:3,自引:1,他引:2
在大量实际资料的基础上,深入研究了西北地区陆相侏罗纪地层中记录的地质事件。从煤层特征、颜色特征、岩性特征、孢粉组合特征、植物群特征和双壳动物化石特征等方面,建立了西北地区陆相侏罗纪地层划分对比的标志。并认为这些生物事件和旋回沉积层的形成都与大范围内侏罗纪古气候变化密切相关,中侏罗世晚期到晚侏罗世末存在一次最为明显的升温事件。 相似文献