秦岭以南地区降水量变化及其灾害效应研究   总被引：4，自引：1，他引：3  

刘引鸽  葛永刚  周旗 《干旱区地理》2008,31(1):50-55

近年来气候变化诱发的灾害效应损失严重。利用秦岭以南地区1951-2001年28个站逐月降水资料,计算了降水量的线性趋势值及降水距平变化,分析了降水量的时间和空间演变特征。受地形影响,秦岭南北与东西降水量变化差异较大,西部大于东部,南坡多于北坡,季节性降水过程差异也很明显;年平均最大降水量为1 254.6 mm,出现在镇巴,最少降水量为690.7 mm,出现在丹凤;50年来降水量变化呈减少趋势,平均递减率为56.5 mm/10 a。分析表明,降水突变是触发其它灾害的主要因素。由强降水及连阴雨诱发的干旱、洪涝及地质灾害效应损失严重,在降雨强度达200 mm/d以上的区域成为泥石流、滑坡灾害,水土流失的多发区,主要分布在秦岭以南多暴雨中心的米仓山、大巴山、佛坪、商南及洛南一带。降水诱发的灾害效应与人类活动也密切相关,这些研究为未来防灾减灾和环境治理提供了依据。  相似文献   

塔里木河下游不同生活型植被对地表的防护效果   总被引：2，自引：1，他引：1  

程皓  李霞  马兰菊  刘刚 《干旱区地理》2008,31(3):373-378

在干旱区植被生态建设过程中,需要进行决策并经常引起争论的问题是,究竟应该选择哪种生活型植被才能获得最大的防护效果.为比较不同生活型植被对地表防护效果的差异,本文选取塔里木河下游6种常见乔灌草植被,以降低风速百分比的平均值作为植被对地表防护效果的评价指标,对不同生活型植被对地表防护效果进行定量比较.结果表明:上述6种植被防风性能大小次序依次为:花花柴>罗布麻>骆驼刺>柽柳>盐穗木>胡杨.花花柴对地表防护效果最好,降低地表风速百分比的平均值达44.00%,胡杨对地表防护效果最差,降低地表风速百分比平均值13.21%.就乔、灌、草不同生活型植被而言,防护效果大小次序为:多年生草本>灌木>乔木.因此,从生态防护效应角度来说,在干旱区植被生态建设中,应坚持灌、草先行的原则,乔木植被只能在水分条件较优越的地区适度发展.只有这样才能充分利用有限的水资源, 取得最佳的生态防护效应.  相似文献   

西南丘陵区土地整理的预期景观效应分析——以重庆市江北区五宝镇大树村为例     

冯应斌  杨庆媛  田永中  吴文戬 《云南地理环境研究》2008,20(2):55-58

在GIS技术的支持下,选取了不同坡度早地的斑面积占项目区实施块总面积、斑块平均面积、斑块平均周长、斑块个数、斑块平均密度、斑块总面积的比例等指标分析了土地整理前后斑块的变化;运用廊道长度、宽度、密度、连通性、环度、各类型廊道长度占项目区廊道总长度的比例等指标分析了整理前后廊道的变化特征。研究结果表明：土地整理后,斑块的平均面积、平均周长增大,斑块个数减少和斑块平均密度变小,形状更加规范化;耕地景观破碎度降低,廊道布局更加合理;各类型廊道结构更加完善,功能更加齐全,各类型廊道的连通性和环度明显提高。  相似文献   

基于数值模拟的三峡库区典型堆积层滑坡变形预测方法     

晏鄂川  朱大鹏  宋琨  林云钿 《吉林大学学报(地球科学版)》2012,42(2):422-429

目前对堆积层滑坡的变形预测大多基于数学模型或方法,忽略了引起滑坡位移显著变化的动力外因及滑坡自身的地质特征,因此,预报准确度和可信度较低。以三峡库区典型堆积层滑坡--鹤峰场镇滑坡为例,通过4组主要控制因素科学组合构建了滑坡的基本地质模型;以此为基础,重点考虑引起滑坡发生变形的库水作用动力因素,建立滑坡的数值-力学模型。通过实际监测点的变形监测结果与数值-力学模型中模型监测点的变形进行拟合分析,获取了实际时间与数值-力学模型中时步的等效关系;基于时间-时步等效关系及三峡水库设计水位调度曲线,得到了不同时步水位的波动特征;通过时步的外延,并在相应的时步段对数值-力学模型施加等效时间的库水作用,预测了滑坡在未来库水位变动条件下的变形。该预测方法既考虑了滑坡的工程地质模型又考虑了地下水作用效应,克服了纯数学方法预测的不足。  相似文献   

花岗岩低温热力效应参数及强度规律研究     

李云鹏  王芝银 《岩土力学》2012,33(2):321-326

长期处于变低温环境中的岩石热力学效应主要表现为材料的力学特性参数、热力系数和饱和冻结状态孔隙冰胀系数等随温度改变而发生变化,这种变化对岩体的变形及强度特性均有显著影响。根据变物性参数的非线性热弹性理论,建立了考虑热力系数和冰胀力系数的本构方程,给出了单轴压缩条件下热力效应系数随温度变化的分析格式和确定方法;借助于花岗岩不同低温干燥和饱和冻结状态的单轴压缩试验资料,获得了花岗岩低温热力效应与温度的关系,并探讨了其对花岗岩抗压强度的影响特性。分析表明,在变低温环境下花岗岩热力系数和冰胀力系数均随相对温差的增大而逐渐减小,热力系数降低速率小于冰胀系数降低速率,在同一温差下热力系数大于冰胀系数;热应力和冰胀应力与温度改变量呈非线性增长关系;花岗岩抗压强度在两种状态下均呈增大趋势,但主要以热应力为主,热力系数引起的试样轴向应力增量总是大于冰胀力引起的轴向应力增量。所给方法及研究成果可用于长期处于变低温状态下材料的力学性能研究及其工程应用。  相似文献   

Seismic motion in urban sites consisting of blocks in welded contact with a soft layer overlying a hard half-space     

Jean-Philippe Groby  Armand Wirgin 《Geophysical Journal International》2008,172(2):725-758

We address the problem of the response to a seismic wave of an urban site consisting of   N _b   blocks overlying a soft layer underlain by a hard substratum. The results of a theoretical analysis, appealing to a space–frequency mode-matching (MM) technique, are compared to those obtained by a space–time finite-element (FE) technique. The two methods are shown to give rise to the same prediction of the seismic response for   N _b = 1  , 2 and 40 blocks. The mechanism of the interaction between blocks and the ground, as well as that of the mutual interaction between blocks, are studied. It is shown, in the first part of this paper, that the presence of a small number of blocks modifies the seismic disturbance in a manner which evokes qualitatively, but not quantitatively, what was observed during the 1985 Michoacan earthquake in Mexico City. Anomalous earthquake response at a much greater level, in terms of duration, peak and cumulative amplitude of motion, is shown, by a theoretical and numerical analysis in the second part of this paper, to be induced by the presence of a large (≥10) number of identical equi-spaced blocks that are present in certain districts of many cities.  相似文献   

Analysis of three-component ambient vibration array measurements   总被引：1，自引：0，他引：1  

Donat Fäh  Gabriela Stamm  Hans-Balder Havenith 《Geophysical Journal International》2008,172(1):199-213

  相似文献   

Seismic vertical array analysis for phase decomposition     

Kunikazu Yoshida  Tsutomu Sasatani 《Geophysical Journal International》2008,174(2):707-718

We propose a vertical array analysis method that decomposes complex seismograms into body and surface wave time histories by using a velocity structure at the vertical array site. We assume that the vertical array records are the sum of vertically incident plane P and S waves, and laterally incident Love and Rayleigh waves. Each phase at the surface is related to that at a certain depth by the transfer function in the frequency domain; the transfer function is obtained by Haskell's matrix method, assuming a 1-D velocity structure. Decomposed P , S and surface waves at the surface are estimated from the vertical array records and the transfer functions by using a least-squares method in the frequency domain; their time histories are obtained by the inverse Fourier transform. We carried out numerical tests of this method based on synthetic vertical array records consisting of vertically incident plane P and S waves and laterally incident plane Love and Rayleigh waves. Perfect results of the decomposed P , S , Love and Rayleigh waves were obtained for synthetic records without noise. A test of the synthetic records in which a small amount of white noise was added yielded a reasonable result for the decomposed P , S and surface waves. We applied this method to real vertical array records from the Ashigara valley, a moderate-sized sedimentary valley. The array records from two earthquakes occurring at depths of 123 and 148 km near the array (epicentral distance of about 31 km) exhibited long-duration later phases. The analysis showed that duration of the decomposed S waves was a few seconds and that the decomposed surface waves appeared a few seconds after the direct S -wave arrival and had very long duration. This result indicated that the long-duration later phases were generated not by multireflected S waves, but by basin-induced surface waves.  相似文献   

黄河源区玛多县沙漠化成因与发展过程     

姚正毅  李晓英  董治宝 《冰川冻土》2015,37(5):1245-1256

通过分析黄河源区玛多县沙漠化的成因和过程,结果表明,玛多县沙漠化成因类型有三种,分别为固定沙丘/古沙丘活化、滑塌陡坎及风蚀斑块,其形成都与多年冻土退化相关.在固定沙丘或古沙丘分布区,冻土退化导致热融沉陷,形成沉陷坑,沉陷坑边缘形成拉裂缝或陡坎,使下伏松散沙露出.在斜坡上,冻土退化形成滑塌陡坎,使底层土壤从侧面暴露.在平坦的冲积平原,差异性冻胀和融沉导致草皮拉裂,形成积水坑洼,冻土退化导致土壤变干,土壤的底层暴露.下伏风成沉积物暴露后,遭受风蚀,形成侧向凹槽,致使上部土体坍塌,使更多的风成沉积物暴露,这些过程的不断重复,使风蚀坑、陡坎、风蚀斑块扩大相连,最终形成流动沙丘、风蚀劣地、戈壁等地貌.  相似文献   

Comparison of 1D linear,equivalent-linear,and nonlinear site response models at six KiK-net validation sites     

《Soil Dynamics and Earthquake Engineering》2015

Vertical seismometer arrays represent a unique interaction between observed and predicted ground motions, and they are especially helpful for validating and comparing site response models. In this study, we perform comprehensive linear, equivalent-linear, and nonlinear site response analyses of 191 ground motions recorded at six validation sites in the Kiban–Kyoshin network (KiK-net) of vertical seismometer arrays in Japan. These sites, which span a range of geologic conditions, are selected because they meet the basic assumptions of one-dimensional (1D) wave propagation, and are therefore ideal for validating and calibrating 1D nonlinear soil models. We employ the equivalent-linear site response program SHAKE, the nonlinear site response program DEEPSOIL, and a nonlinear site response overlay model within the general finite element program Abaqus/Explicit. Using the results from this broad range of ground motions, we quantify the uncertainties of the alternative site response models, measure the strain levels at which the models break down, and provide general recommendations for performing site response analyses. Specifically, we find that at peak shear strains from 0.01% to 0.1%, linear site response models fail to accurately predict short-period ground motions; equivalent-linear and nonlinear models offer a significant improvement at strains beyond this level, with nonlinear models exhibiting a slight improvement over equivalent-linear models at strains greater than approximately 0.05%.  相似文献