On the Importance of Geolithological Features for the Estimate of the Site Response: The Case of Catania Metropolitan Area (Italy)     

G. Lombardo  H. Langer  S. Gresta  R. Rigano  C. Monaco  G. De Guidi 《Natural Hazards》2006,38(3):339-354

The evaluation of seismic site response in the urban area of Catania was tackled by selecting test areas having peculiar lithological and structural features, potentially favourable to large local amplifications of ground motion. The two selected areas are located in the historical downtown and in the northern part of Catania where the presence of a fault is evident. Site response was evaluated using spectral ratio technique taking the horizontal- to-vertical component ratio of ambient noise. Inferences from microtremor measurements are compared with results from synthetic accelerograms and response spectra computed at all drillings available for this area. Such method is particularly suitable in urban areas where the nature of the outcropping geological units is masked by city growth and anthropic intervention on the surface geology. The microtremor H/V spectral ratios evaluated at soft sites located within the downtown profile tend to be smaller than that usually reported in the literature for such soils. A tendency for amplifications to peaks near 2 Hz is observed only in some sites located on recent alluvial deposits. Evidences for amplifications of site effects (frequency range 4–8 Hz) were observed in the sampling sites located on the fault, with a rapid decrease of spectral amplitude just a few tenths of metres away from the discontinuity. Numerical simulations evidenced the importance of geolithological features at depth levels even greater than 20–30 m. Besides this, the results strongly confirm the importance of the subsurface geological conditions, in the estimate of seismic hazard at urban scale.  相似文献   

Poverty, vulnerability and the impact of flooding in the Limpopo Province, South Africa   总被引：1，自引：0，他引：1  

Masingita Khandlhela  Julian May 《Natural Hazards》2006,39(2):275-287

The article evaluates household vulnerability after the 2000 flood in two poor communities of the Limpopo Province, South Africa. The study analyses the forms of vulnerability which disasters such as floods present. Using data gathered from a survey of households, the study presents the impacts, coping and adapting strategies of households after the 2000 flood. The article argues that beyond the concern over socio-economic circumstances as the major determinant of household vulnerability, the management of the disaster can serve to perpetuate vulnerability.  相似文献   

Effect of a submerged bay-mouth breakwater on tsunami behavior analyzed by 2D/3D hybrid model simulation     

Koji Fujima 《Natural Hazards》2006,39(2):179-193

The hybrid numerical model had been developed to simulate a complicated 3D flow around structures generated by tsunami. In the model, the conventional 2D model is adopted for the wide region far from structures and the 3D non-hydrostatic pressure model is used in the limited region adjacent to structures. The applicability of the model is shown by comparisons of the numerical results with the experimental results of the laboratory model tests and the numerical analysis results of the conventional whole 2D simulation. In addition, the effect of a submerged structure at the opening of a breakwater is discussed from the numerical simulations by the hybrid model. The submerged structure improves the stability of the rubble mound and reduces the tsunami inflow into the bay, while it increases the water surface velocity around the opening of the breakwater. The increase of surface velocity causes the increases of impulsive forces by collision with drafts and so on.  相似文献   

大渡河上游不同地带居民对环境退化的响应   总被引：6，自引：2，他引：6  

阎建忠  张镱锂  朱会义  摆万奇  郑度 《地理学报》2006,61(2):146-156

青藏高原的环境退化引起了极大的关注,但农牧民如何认识和响应环境退化,还缺乏实证研究.采用参与性农村评估法,对大渡河上游不同地带典型村（位于河谷区的丹扎木村、中山区的克尔马村和山原区的日科村）的农牧民进行调查和对比分析.研究表明：①大渡河上游不同地带的居民对环境退化具有不同的响应过程.河谷区通过劳动力向二、三产业转移,缓解了人口压力,采取积极的措施来应对自然灾害和森林退化;中山区以劳动力向二、三产业转移和发展畜牧业来缓解人口压力,没有采取积极的措施应对环境退化：山原区的劳动力不能转移到二、三产业,只能通过增加牲畜数量来解决生计,牧民仅采取一些积极的措施来应对草料不足的问题和雪灾等自然灾害.在大渡河上游,最脆弱的区域是中山区和山原区,而不是人口压力大的河谷区.②生计方式是影响居民响应人口压力和环境退化的关键因素.基于居民的生计方式来解释和解决生态脆弱区的人口压力和环境退化问题,将是一个新的方向.③劳动力向二、三产业转移有利于居民改善生计.降低教育收费和进行基础设施建设,将加快劳动力向二、三产业转移.  相似文献   

三角洲前缘岸滩对河流来沙减少响应的敏感性探讨——以长江口门区崇明岛向海侧岸滩为例   总被引：2，自引：2，他引：2  

杨世伦  李明  张文祥 《地理与地理信息科学》2006,22(6):62-65

利用ArcGIS对1977—2004年不同时段的长江口崇明岛向海侧水下地形测量资料进行处理,并结合该区的潮滩历史遥感图片、现场高程测量以及同期大通站输沙率资料,探讨三角洲前缘岸滩冲淤演变对河流来沙减少响应的敏感性。结果表明:研究区岸滩的淤涨速率总体上在年代以上时间尺度随着长江来沙减少而下降,但由于局部滩—槽演变和海洋动力条件的影响,某些年代内和某些部位可能出现相反的趋势,使岸滩演变对河流来沙减少的响应变得复杂化。在此基础上预测今后几十年研究区的冲淤趋势。  相似文献   

农户对禁牧政策的行为响应及其影响因素研究——以新疆策勒县为例   总被引：13，自引：4，他引：13  

马骅  吕永龙  邢颖  孙亚梅 《干旱区地理》2006,29(6):902-908

以新疆策勒县为例,对当地农牧民在封育禁牧影响下的经济行为响应及其影响因素利用对数线性模型进行定量分析,以研究不同背景条件的农牧民在进行行为选择时的规律性因素。研究表明,农户所属区域及其拥有的资本水平是农户对禁牧行为响应的显著影响因素;农户所属区域及当地的技术服务培训等政策配套水平是农户对禁牧态度的显著影响因素;农牧民畜牧生产观念的转变和草场承包责任制的落实是实施禁牧政策的先决条件。建议政府针对区域及农户的资本差异进行分类补偿;当地政府可整合利用各相关部门的项目资源和资金进行禁牧的政策前期和推广工作。  相似文献   

Surface temperature differences between minerals in crystalline rocks: Implications for granular disaggregation of granites through thermal fatigue   总被引：4，自引：0，他引：4  

Miguel Gmez-Heras  Bernard J. Smith  Rafael Fort 《Geomorphology》2006,78(3-4):236-249

Thermal expansion differences between minerals within rocks under insolation have previously been assumed to drive breakdown by means of granular disaggregation. However, there have been no definitive demonstrations of the efficacy of this weathering mechanism. Different surface temperatures between minerals should magnify thermal expansion differences, and thus subject adjacent minerals to repeated stresses that might cause breakdown through fatigue failure. This work confirms the existence of surface temperature differences between minerals in granitic rocks under simulated short-term temperature fluctuations so as to discriminate their potential for initiating granular disaggregation. The influence of colour, as a surrogate for albedo, and crystal size, as a function of thermal mass are specifically identified because of their ease of quantification. Four rock types with a range of these properties were examined, and subjected to repeated short-term temperature cycles by radiative heating and cooling under laboratory conditions. Results show that while albedo is the main control for overall and individual maximum temperatures, crystal size is the main factor controlling higher temperature differences between minerals. Thus, stones with large differences of mineral sizes can undergo magnified stresses due to thermal expansion differences.  相似文献   

A greenhouse study on root dynamics of cactus pears, Opuntia ficus-indica and O. robusta     

H.A. Snyman   《Journal of Arid Environments》2006,65(4):529-542

Over the last 10 years a great interest in spineless cactus pear was shown in the drier areas in terms of both fresh fruit and fodder production. However, there is a lack of knowledge on quantitative data on root dynamics of these plants needed to fully understand its potential under water limiting conditions. This study aimed at quantifying the effects of water stress on the growth of tap roots, side roots and rain roots of the species Opuntia ficus-indica (L.) Miller (cultivar Morado—green cladode) and O. robusta Wendl. (cultivar Monterey—blue cladode). One-year-old cladodes were planted in root boxes and pots (2002/2003 season) that were kept in the greenhouse at day/night temperatures of 25–30 °C/15–18 °C. Placing the cladodes flat on the soil, more areoles came in contact with the soil and therefore more roots developed in both species with an average of only 3.4% areole complexes not rooting. Each areole complex formed on average 3 roots. The highest daily tap root growth was 42 and 36 mm for O. ficus-indica and O. robusta, respectively. Tap root growth increased in the morning with water stress for both species but decreased in the afternoon. Side root growth increased with water stress, with that of O. robusta more per tap root than O. ficus-indica. O. robusta showed a finer root system than O. ficus-indica. The side roots grew as much as 8 and 5 mm per day for O. ficus-indica and O. robusta, respectively. Whitish rain roots developed on the established roots within the first hour after rewetting the soil and grew for only 3 days. Rain roots grew up to 7 and 5 mm within a day for O. ficus-indica and O. robusta, respectively. Considering all studied aspects of their roots systems, O. robusta appears to be better adapted to drought (less sensitive to water stress) than O. ficus-indica.  相似文献   

Strain partitioning and stress rotation at the North Anatolian fault zone from aftershock focal mechanisms of the 1999 Izmit M_w= 7.4 earthquake     

Marco Bohnhoff  Helmut Grosser  Georg Dresen 《Geophysical Journal International》2006,166(1):373-385

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Traction image method for irregular free surface boundaries in finite difference seismic wave simulation   总被引：16，自引：1，他引：16  

Wei Zhang  Xiaofei Chen 《Geophysical Journal International》2006,167(1):337-353

In this study, we propose a new numerical method, named as Traction Image method, to accurately and efficiently implement the traction-free boundary conditions in finite difference simulation in the presence of surface topography. In this algorithm, the computational domain is discretized by boundary-conforming grids, in which the irregular surface is transformed into a 'flat' surface in computational space. Thus, the artefact of staircase approximation to arbitrarily irregular surface can be avoided. Such boundary-conforming gridding is equivalent to a curvilinear coordinate system, in which the first-order partial differential velocity-stress equations are numerically updated by an optimized high-order non-staggered finite difference scheme, that is, DRP/opt MacCormack scheme. To satisfy the free surface boundary conditions, we extend the Stress Image method for planar surface to Traction Image method for arbitrarily irregular surface by antisymmetrically setting the values of normal traction on the grid points above the free surface. This Traction Image method can be efficiently implemented. To validate this new method, we perform numerical tests to several complex models by comparing our results with those computed by other independent accurate methods. Although some of the testing examples have extremely sloped topography, all tested results show an excellent agreement between our results and those from the reference solutions, confirming the validity of our method for modelling seismic waves in the heterogeneous media with arbitrary shape topography. Numerical tests also demonstrate the efficiency of this method. We find about 10 grid points per shortest wavelength is enough to maintain the global accuracy of the simulation. Although the current study is for 2-D P-SV problem, it can be easily extended to 3-D problem.  相似文献