非对称大底盘双塔连体结构的动力特性和地震响应分析          下载免费PDF全文

郭涛  宋娟  姚激  魏业清 《地震工程学报》2009,31(3):254-258,264

依据现行抗震设计规范,运用三维有限元软件ANSYS对某25层大底盘非对称双塔连体结构进行了时程法地震反应分析,得到结构的自振特性和地震响应,并与未设连体的双塔结构的结果进行了比较.结果表明增设连体后双塔的扭转振型更加丰富,且运动和变形得到了统一和协调.  相似文献   

蒙城地震台地电阻率各向异性参量研究     

曾献军  陈俊  张娟  薛志名  于林民  汪继林  刘红飞  李雪华  周琼 《地震地磁观测与研究》2009,30(3):21-26

地电阻率各向异性参量计算方法是由钱复业,赵玉林等研究出来的方法。我们试用该方法编制相应的计算机程序,对蒙城地震台1978～2008年地电阻率的数据进行处理;并结合震例进行对比分析,发现对于震中距300km内的中强震,与地电阻率各向异性参数的趋势性变化存在密切的关系;地电阻率各向异性参量特征可以反映孕震区地下介质的孕震信息,对未来地震的预测将起到一定作用。  相似文献   

小波变换在关中井水位资料分析中的应用   总被引：2，自引：0，他引：2  

邢西淳  毛娟  邵辉成  张世民 《高原地震》2009,21(4):1-8

利用小波变换和多尺度分析原理,对周至井、三原井7年的水位日均值序列进行了分析,将周至井、三原井水位资料中的不同周期成分进行了有效分离,小波变换分解结果能够更直观和显著地反映地震活动,特别是印尼8．7级、汶川8．0级特大地震及其中强余震异常显示明显。对甘东南地区的5级以上地震也有较明显的前兆反映,表明小渡分析在处理和分析水位资料方面是一种有效的方法。  相似文献   

Geochemistry,chronology and stratigraphy of Neogene tuffs of the Central Andean region     

Christa Placzek  Jay Quade  Jason A. Rech  P.J. Patchett  Carlos Pérez de Arce 《Quaternary Geochronology》2009,4(1):22-36

Tuff layers are vital stratigraphic tools that allow correlations to be made between widely dispersed exposures. Despite their widespread occurrence in the central Andes, tuffs from both natural exposures and sedimentary cores extracted from the region's extensive salars (salt pans) are relatively unstudied. Here we lay the foundation for a tephrostratigraphic framework in the central Andes (14–28°S) by chemically and morphologically characterizing ash shards, and in some cases dating 36 Neogene distal tuffs. These tuffs occur in lacustrine and alluvial deposits from the southern Bolivian Altiplano and adjacent Atacama Desert. All tuffs are calc-akaline rhyolites, consistent with their setting in the Central Andean Volcanic Zone. Five of the older tuffs were ⁴⁰Ar/³⁹Ar dated and yield an age range of 6.63–0.75 Ma. Organic material associated with tuffs deposited into paleolake sediments, paleowetland deposits, or urine-encrusted rodent middens provide constraints on the age of several Late Pleistocene and Holocene tuffs.These tuffs provide key stratigraphic markers and ages for lake cycles and archeological sites on the Bolivian Altiplano and for assessing rates of surficial processes and archeology in both the Atacama and Altiplano. While modern climate, and consequently questions about geomorphic processes and climate change, differs in the hyperarid Atacama and the semi-arid Altiplano, the most extensive air-fall tuffs covered both regions, placing the Atacama and the Bolivian Altiplano in the same tephrostratigraphic province. For example, the Escara B tuff (～1.85 Ma), can be securely identified in both the Altiplano and Atacama. On the Altiplano, dates from the Escara B and E tuffs securely establish the age of the Escara Formation—representing the oldest expansive lake documented on the Bolivian Altiplano. By contrast, the presence of the Escara B tuff below ～6 m of alluvial sediment at the Blanco Encalado site in the Atacama desert yields information about sedimentation rates in this hyperarid region. Indeed, most tuffs from the Atacama Desert are older than 600,000 years, even though they occur within fluvial terraces immediately adjacent to the alluvial fans that are still active. Most of these geomorphic surfaces in the Atacama also possess well-developed saline soils that, when combined with the radiometric ages of the distal tuffs, suggest slow rates of geomorphic change and exceptional landscape stability for this area during the Quaternary.In contrast, younger tuffs are more abundant in the more recent lake records of the Altiplano. The Chita tuff was deposited at ～15,650 cal yr B.P., during the regressive phase of the region's deepest late Quaternary lake cycle—the “Tauca lake cycle”—which spanned 18.1–14.1 cal yr B.P. Two Holocene tuffs, the Sajsi tuff and the Cruzani Cocha tuff, are widespread. The Sajsi tuff was deposited just before 1700 cal yr B.P., whereas the Cruzani Cocha tuff appears to be mid-Holocene in age and shows some chemical affinities to a Holocene tuff (202B) deposited between 4420 and 5460 cal yr B.P. in a urine-encased rodent midden in the Atacama Desert.  相似文献   

陕西咸阳人工林地土壤干层研究   总被引：20，自引：4，他引：16  

赵景波  杜娟  周旗  岳应利 《地理科学》2005,25(3):322-328

根据咸阳庞西村苹果林地、梧桐林地和草地土壤含水量测定,研究了0~6m土壤含水量的变化和土壤干层特点与分布。结果显示, 咸阳人工林地从表层向下含水量呈现由高到低再到低的变化;10龄苹果林地2~4m深处土壤含水量平均为8.3%,12龄梧桐林2~4m深处土壤含水量平均为8.6%,均发育了明显的土壤干层;4龄苹果林下土层有干化显示,但无干层发育;草地土层含水量明显较苹果林地高,无土壤干化的显示。研究表明,土壤干层形成的具体原因一是降水量少决定的薄膜水带埋藏深度小,二是薄膜水的运移速度缓慢和含水量低。为保持人工林基本正常的生长和土壤水的正常运移,应避免严重的土壤干层出现。咸阳附近土壤干层的出现表明土壤干层在黄土高原广泛分布,该区的植被恢复首先应以疏林或森林草原为主,待土壤水分改善后再考虑恢复森林植被。  相似文献   

南疆盆地沙尘气溶胶光学特性及我国沙尘天气强度划分标准的研究   总被引：13，自引：13，他引：0  

李霞  胡秀清  崔彩霞  李娟 《中国沙漠》2005,25(4):488-495

依据气溶胶光学厚度测量原理,利用布设于塔里木盆地腹地塔中和盆地西南边缘和田气象站的2部CE318自动跟踪太阳光度计于2002年6月至2003年11月期间的探测结果,结合地面气象实测资料,分析了南疆盆地大气气溶胶的光学特性。同时结合我国已有的沙尘气溶胶光学特性的研究成果,初步提出了依据气溶胶光学厚度判断沙尘天气强度的标准。结果表明:塔中、和田气溶胶光学厚度随波长的增大多呈现减小趋势,塔中个别季节有些例外;2站气溶胶光学厚度的日变化基本保持对称的抛物线形,在春、夏季尤为明显;Angstrom浑浊度系数β的拟合曲线显示β随能见度增大而减小,波长指数α随能见度的变化趋势说明弱沙尘天气下,大气中主要弥漫着小粒径的气溶胶颗粒,而强沙尘天气则以大粒径为主;沙尘气溶胶光学厚度随晴空、浮尘、扬沙、沙尘暴依次增加;沙尘天气发生时,气溶胶光学厚度的临界值基本为晴空值的两倍,沙漠地区气溶胶光学厚度≥1.1206,北京≥0.3174。而发生沙尘暴的阈值则有很大不同,沙漠区气溶胶光学厚度至少 > 3.0,北京由于大气污染等因素,其判断沙尘暴发生的阈值为1.9982。另外笔者认为AOD与水平能见度之比值能够较全面地考虑水平和垂直两个方向的要素变化,衡量沙尘天气强度更具有合理意义,值得更深一步的探讨。  相似文献   

考虑非达西流的弱透水层固结计算   总被引：13，自引：1，他引：12  

谢海澜  武强  赵增敏  金晓丽  李娟 《岩土力学》2007,28(5):1061-1065

由于成岩作用的影响,深部弱透水层中的黏性土较为坚硬、致密,在这种黏土层中的孔隙渗流规律有偏离达西定律的现象,而在现有的地面沉降研究中,对深部弱透水层的固结变形计算始终沿用以达西定律为基础的固结方程进行,这显然是与实际情况不相符的。鉴于此,以孔隙渗流为非达西流为基础,对太沙基一维固结方程进行了重新推导,并采用半解析法对非达西流-太沙基一维固结方程进行了求解。分别采用达西流-太沙基固结方程和非达西流-太沙基固结方程对同一固结问题进行了计算,结果表明,考虑非达西流后土层达到某一固结度所需的固结时间较之不考虑非达西流时明显增加了,而且固结时间增长的趋势与实测的增长趋势较为一致。  相似文献   

汕头市土地利用空间格局的景观生态学分析   总被引：5，自引：0，他引：5  

王娟  陈绍愿  林建平 《热带地理》2006,26(3):223-228

根据不同利用类型土地生态效应的异同,对汕头市2003年1∶1万比例尺土地更新调查数据的土地分类系统进行调整,将全部土地景观划分为耕地、林地、园地、草地、居民点及工矿、交通、裸土地和水域等8类.在GIS的支持下,提取各类型土地景观斑块的数目、面积和周长等信息,据此对斑块景观的数量、面积和形状等特征,以及区域景观的多样性、均匀度和优势度,集中性和区际意义等进行分析,从而总结出全市范围及六区一县土地利用空间格局的景观生态学特征.  相似文献   

Improving the Elevation Accuracy of Digital Elevation Models: A Comparison of Some Error Detection Procedures   总被引：1，自引：1，他引：0  

Carlos López 《Transactions in GIS》2000,4(1):43-64

The widespread availability of powerful desktop computers, easy‐to‐use software tools and geographic datasets have raised the quality problem of input data to be a crucial one. Even though accuracy has been a concern in every serious application, there are no general tools for its improvement. Some particular ones exist, however, and some results are presented here for a particular case of quantitative raster data: Digital Elevation Models (DEM). Two procedures designed to detect anomalous values (also named gross errors, outliers or blunders) in DEMs, but valid also for other quantitative raster datasets, were tested. A DEM with elevations varying from 181 to 1044 m derived from SPOT data has been used as a contaminated sample, while a manually derived DEM obtained from aerial photogrammetry was regarded as the ground truth to allow a direct performance comparison for the methods with real errors. It is assumed that a “better” value can be measured or obtained through some methodology once an outlier location is suggested. The options are different depending upon the user (DEM producers might go to the original data and make another reading, while end users might use interpolation). Both choices were considered in this experiment. Preliminary results show that for the available dataset, the accuracy might be improved to some extent with very little effort. Effort is defined here as the percentage of points suggested by the methodology in relation with its total number: thus 100 per cent effort implies that all points have been checked. The method proposed by López (1997) gave poor results, because it has been designed for errors with low spatial autocorrelation (which is not the case here). A modified version was then designed and compared with the method proposed by Felicísimo (1994). The three procedures can be applied both for error detection during DEM generation and by end users, and they might be of use for other quantitative raster data. The choice of the best methodology is different depending on the effort involved. The conclusions have been derived for a photogrammetrically obtained DEM; other production procedures might lead to different results.  相似文献   

CO2-rich thermomineral groundwater in the Betic Cordilleras, southeastern Spain: Genesis and tectonic implications     

J. C. Cerón  M. Martín-Vallejo  L. García-Rossell 《Hydrogeology Journal》2000,8(2):209-217

The CO₂-rich thermal groundwater in the Betic Cordilleras in Spain has been studied with regard to the geological and hydrogeological setting, physical and chemical characteristics, and ¹³C-isotope content. The study area is about 60 km northeast of Almería city, in southeastern Spain. The thermomineral waters are plentiful and are related to regional geothermal anomalies. Temperatures of 20 −41°C, high bicarbonate concentrations (183–1824 mg/L), and high amounts of PCO₂ (<1.1 bar) characterize the groundwater. CO₂ spatial variations are related to proximity to the Carboneras, Palomares, and Guadalentín fault systems, which may be the surface representation of the zone of crustal thinning and magmatism. δ ¹³C values probably indicate a deep source for the CO₂, either the mantle or perhaps carbonate rocks in the metamorphic substratum. The high amount of CO₂ in the groundwater causes problems in wells and severely restricts water usage. The hydrothermal features of this area are probably related to neotectonic activity. Received, September 1998/Revised, June 1999, September 1999/Accepted, December 1999  相似文献