喀斯特高原盆地聚落空间演变——以贵州省红枫湖水系盆地为例   总被引：3，自引：0，他引：3  

周晓芳  周永章  欧阳军 《地域研究与开发》2012,31(3):145-150

贵州是我国喀斯特分布最广的地区,喀斯特高原盆地是贵州主要的人口聚集地。充分认识高原盆地聚落的空间分布及其演化态势,对区域城镇规划、社会主义新农村建设及可持续发展有重要意义。以红枫湖水系盆地为例,基于GIS技术及相关软件,主要利用景观格局指数、Moran’s I系数以及居民点数据与等高线数据的空间叠置及转换技术,从水平和垂直两个维度对案例地区聚落空间分布的变化进行研究。研究表明:喀斯特高原盆地聚落的空间分布和演变具有强烈的喀斯特地域基因,在喀斯特地貌的限制下聚落总体分布分散;近年来聚落规模不断增加,在局部有一定小规模集聚并随地形限制而表现出不同的集聚形式和集聚程度;而随着数量的增多和规模的增大,聚落形态更为复杂且景观趋于破碎,空间分布更加复杂;喀斯特地貌的垂直空间特点在决定聚落的垂直分布及演变规律的同时也加剧了聚落空间分布的复杂性。  相似文献   

Evaluating the sensitivity of wetlands to climate change with remote sensing techniques   总被引：1，自引：0，他引：1       下载免费PDF全文

Zutao Ouyang  Richard Becker  Wade Shaver  Jiquan Chen 《水文研究》2014,28(4):1703-1712

Wetlands are valuable ecosystems that provide many valuable services, yet many of these important ecosystems are at risk because of current trends in climate change. The Prairie Pothole Region (PPR) in the upper‐midwest of the United States and south‐central Canada, characterized by glacially sculpted landscapes and abundant wetlands, is one such vulnerable region. According to regional/global climate model predictions, drought occurrence will increase in the PPR region through the 21st century and thus will probably cause the amount of water in wetlands to decline. Water surface area (WSA) of Kidder County, ND, from 1984–2011 was measured by classifying TM/ETM+(Landsat Thematic Mapper / Enhanced Thematic Mapper Plus) images through the modified normalized difference water index. We then developed a linear model based on the WSA of these wetlands and historical climate data and used this to determine the wetland sensitivity to climate change and predict future wetlands WSA in the PPR. Our model based on Palmer drought severity index (PDSI) of the current year (PDSI_{t ? 0}) and of the previous two years (PDSI_{t ? 2}) can explain 79% of the annual wetland WSA variance, suggesting a high sensitivity of wetlands to drought/climate change. We also predicted the PPR wetlands WSA in the 21st century under A1B scenario (a mid‐carbon emission scenario) using simulated PDSI based on Intergovernmental Panel on Climate Change AR4 22‐model ensemble climate. According to our prediction, the WSA of the PPR wetlands will decrease to less than half of the baseline WSA (defined as the mean wetlands WSA of the 2000s) by the mid of the 21st century, and to less than one‐third by the 2080s, and will then slightly increase in the 2090s. This considerable future wetland loss caused only by climate change provides important implication to future wetland management and climate adaptation policy. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Seismic inversion with generalized Radon transform based on local second-order approximation of scattered field in acoustic media          下载免费PDF全文

Wei Ouyang  Weijian Mao  Xuelei Li  Wuqun Li 《地震科学（英文版）》2014,27(4):433-439

Sound velocity inversion problem based on scattering theory is formulated in terms of a nonlinear integral equation associated with scattered field. Because of its nonlinearity, in practice, linearization algorisms (Born/single scattering approximation) are widely used to obtain an approximate inversion solution. However, the linearized strategy is not congruent with seismic wave propagation mechanics in strong perturbation (heterogeneous) medium. In order to partially dispense with the weak perturbation assumption of the Born approximation, we present a new approach from the following two steps: firstly, to handle the forward scattering by taking into account the second-order Born approximation, which is related to generalized Radon transform (GRT) about quadratic scattering potential; then to derive a nonlinear quadratic inversion formula by resorting to inverse GRT. In our formulation, there is a significant quadratic term regarding scattering potential, and it can provide an amplitude correction for inversion results beyond standard linear inversion. The numerical experiments demonstrate that the linear single scattering inversion is only good in amplitude for relative velocity perturbation ( \( \delta_{c}/c_{0} \) ) of background media up to 10 %, and its inversion errors are unacceptable for the perturbation beyond 10 %. In contrast, the quadratic inversion can give more accurate amplitude-preserved recovery for the perturbation up to 40 %. Our inversion scheme is able to manage double scattering effects by estimating a transmission factor from an integral over a small area, and therefore, only a small portion of computational time is added to the original linear migration/inversion process.  相似文献   

拟建哈—佳铁路工程地震安评抗断参数研究——以依兰-伊通断裂为例   总被引：1，自引：1，他引：0  

余中元  韦庆海  王丽梅  马艳丽  张立忱  欧阳兆国 《震灾防御技术》2014,9(1):53-63

在对依兰-伊通断裂通河段晚第四纪活动参数获取的基础上,对该断裂的几何学特征和晚第四纪活动特征及有关拟建铁路地震安全的设防参数进行了探讨.研究结果表明,依兰-伊通断裂通河段总体走向N30-40°E,由3条断层组成,中支最新活动时代为全新世.该断裂未来发生7级地震时的水平位移量可能达2.2m左右,垂直位错量约为1.1m左右.该断裂全新世以来的活动性质表现为右旋走滑为主,兼具逆冲活动.根据探槽结果和野外地震地质调查得出断裂垂直位错约（1.0±0.2）m,右旋位错量约为（2.7±0.1）m,（1730-30）aB.P.以来的垂直滑动速率和水平滑动速率分别约为（0.57±0.11）mrn/a和（1.57±0.06）mm/a.未来100年内若遭遇地震,其最大水平位错量约2.87m,垂直位错值为1.04m.断层影响带宽度约为8m.该研究结果为拟建哈—佳铁路工程可能遭受的断层影响和抗震设防提供了一定的数据基础,也为地震安评中线状工程的抗断评价问题提供了一定的参考.  相似文献   

RZB型深井宽频带地形变综合观测系统的垂向应变测量单元     

陈征  欧阳祖熙  李宏  李涛  吴立恒  范国胜  张钧 《震灾防御技术》2014,9(1):126-132

目前钻孔应变观测一般为水平应变,使用无限岩石平板中的钻孔应力集中模型,可反演出水平应力场分布及变化.如果在此基础上加上垂向应力测量,就可反演出三维应力场分布.本文介绍的RZB型深井宽频带地形变综合观测系统的垂向应变测量单元,外钢筒为波纹管结构,并通过螺旋刻丝、热处理等技术,其垂向等效弹性模量比耦合水泥低一个数量级,同时垂向应变钢筒的水平向等效弹性模量高于垂向弹性模量一个数量级.垂向应变探头的力学结构可以被形象地看成是一个螺旋柱形弹簧,其轴向极易产生弹性形变,而水平向的硬度却得到了极大的加强,因此可在竖井中较为准确地测量轴向应变.  相似文献   

发展钻孔应变观测的战略构想   总被引：13，自引：2，他引：11  

邱泽华  谢富仁  苏恺之  欧阳祖熙 《国际地震动态》2004,(1):7-14

钻孔应变观测正在成为一种与测震和GPS相提并论的地壳形变观测。曾经处于领先地位的我国钻孔应力一应变观测的发展需要回顾历史,面对现实,借鉴国外,放眼长远。建立比测基地、实验场和完善国家前兆监测网,三位一体,应该成为发展我国钻孔应变观测的基本方针。  相似文献   

郯庐断裂中段新生代右行走滑位移   总被引：2，自引：0，他引：2  

黄超  余朝华  张桂林  傅良同  袁志云  范兴燕 《吉林大学学报(地球科学版)》2013,43(3):820-832

依据走滑拉分盆地中盆地沉降（或抬升）速率与边界断层走滑速率之间的数值关系,通过对夹在郯庐断裂中段两分支断层间的潍北凹陷沉积埋藏史的恢复,间接求取郯庐断裂中段新生代右行走滑位移。潍北凹陷内不同构造位置4口井的埋藏史恢复结果表明：凹陷新生代经历了古近纪早、中期的快速沉降,古近纪末-新近纪初的抬升剥蚀和中新世以来的缓慢沉降3个阶段;各阶段的平均沉降速率分别为0.142 9、-0.072 8、0.032 5 km/Ma。通过对太平洋板块与欧亚板块间俯冲速率和方向变化的分析推断,中新世中期（39.5 Ma）太平洋板块由北西向俯冲转而变成正西向俯冲所产生的西南向应力分量是导致新生代郯庐断裂开始右行走滑的主要因素,且走滑活动持续至今。根据走滑活动发生和持续的时间,结合各个时期内潍北凹陷的沉降和抬升速率,计算出郯庐断裂中段新生代右行走滑位移量为15 km左右。  相似文献   

Landscape pattern evolution processes of alpine wetlands and their driving factors in the Zoige Plateau of China   总被引：5，自引：2，他引：3  

BAI Jun-hong  LU Qiong-qiong  WANG Jun-jing  ZHAO Qing-qing  OUYANG Hua  DENG Wei  LI Ai-nong 《山地科学学报》2013,10(1):54-67

Zoige Plateau wetlands are located in the northeastern corner of the Qinghai-Tibet Plateau.The landscape pattern evolution processes in the Zoige Plateau and their driving factors were identified by analyzing the dynamic changes in landscape modification and conversion and their dynamic rates of alpine wetlands over the past four decades.The results showed that the landscape conversion between wetlands and non-wetlands mainly occurred during the period from 1966 to 1986.The marsh wetland area converted from lake and river wetlands was larger because of swamping compared to other wetland landscapes.Meanwhile,the larger area of marsh wetlands was also converted to lake wetlands more than other types of wetlands.The modification processes mainly occurred among natural wetland landscapes in the first three periods.Obvious conversions were observed between wetland and nonwetland landscapes(i.e.,forestland,grassland,and other landscapes) in the Zoige Plateau.These natural wetland landscapes such as river,lake and marsh wetlands showed a net loss over the past four decades,whereas artificial wetland landscapes(i.e.,paddy field and reservoir and pond wetlands) showed a net decrease.The annual dynamic rate of the whole wetland landscape was 0.72%,in which the annual dynamic rate of river wetlands was the highest,followed by lake wetlands,while marsh wetlands had the lowest dynamic rate.The integrated landscape dynamic rate showed a decreasing trend in the first three periods.The changes in wetland landscape patterns were comprehensively controlled by natural factors and human activities,especially human activities play an important role in changing wetland landscape patterns.  相似文献   

A generalized limit equilibrium method for the solution of active earth pressure on a retaining wall     

Chao-jun Ouyang  Qiang Xu  Si-ming He  Yu Luo  Yong Wu 《山地科学学报》2013,10(6):1018-1027

In this paper, a generalized limit equilibrium method of solving the active earth pressure problem behind a retaining wall is proposed. Differing from other limit equilibrium methods, an arbitrary slip surface shape without any assumptions of pre-defined shapes is needed in the current framework, which is verified to find the most probable failure slip surface. Based on the current computational framework, numerical comparisons with experiment, discrete element method and other methods are carried out. In addition, the influences of the inclination of the wall, the soil cohesion, the angle of the internal friction of the soil, the slope inclination of the backfill soil on the critical pressure coefficient of the soil, the point of application of the resultant earth pressure and the shape of the slip surface are also carefully investigated. The results demonstrate that limit equilibrium solution from predefined slip plane assumption, including Coulomb solution, is a special case of current computational framework. It is well illustrated that the current method is feasible to evaluate the characteristics of earth pressure problem.  相似文献   

华北地区地震环境噪声特征研究   总被引：13，自引：4，他引：9       下载免费PDF全文

吴建平  欧阳飚  王未来  姚志祥  袁松涌 《地震学报》2012,34(6):818-829

利用华北流动地震台阵观测的垂直分向连续波形数据, 通过计算功率谱密度和相应的概率密度函数, 对华北地区地震环境噪声特征进行了分析研究. 结果表明, 东部平原和沉积盆地2 Hz以上的高频环境噪声水平与全球新高噪声模型（NHNM）相近, 周期3——18 s的平均噪声水平低于NHNM和新低噪声模型（NLNM）的平均值; 山区及西部高原的高频噪声水平明显低于NHNM, 周期1——18 s的噪声水平大多明显低于NHNM和NLNM的平均值; 不同区域18 s以上周期的噪声水平差异相对较小. 流动地震台阵部分台站的环境噪声存在明显的昼夜变化, 个别台站噪声水平明显高于周边台站, 表明这些台站受人类活动干扰较大. 不同台站的噪声水平分析表明, 将台站布设在摆坑内, 能在一定程度上降低高频和低频段的噪声水平. 台站环境噪声特征的研究结果可为流动地震台阵观测数据质量的定量评估, 观测期间的台站优化调整等提供重要依据.   相似文献