月内尺度北半球环状模水平和垂直活动特征分析

采用李建平等定义的更好表征北半球环状模变化的指数,利用NCEP/NCAR逐日再分析资料,从对流层的角度分析了北半球环状模在月内时间尺度上的相关环流的垂直和水平传播特征.结果表明,在水平方向上,温度异常在对流层,尤其是近地层,表现为由极区和高纬度地区向中低纬度地区强的南传特征,而在平流层则为由中低纬度地区向高纬度地区弱的...     

磁层顶日下点距离R0与磁暴Dst指数的相关性

利用2004—2006年ACE、WIND卫星观测的太阳风数据和相应时期反映磁暴大小的〖WTB1X〗D〖WTB1〗st指数,针对200个不同级别的磁暴事件,分析了磁层顶日下点距离〖WTB1X〗R0与磁暴D〖WTB1〗st指数的线性相关性。分析显示,在极端太阳风条件下,〖WTB1X〗D〖WTB1〗st指数时间序列比借助于Chao Model计算出的磁层顶日下点距离〖WTB1X〗R〖WTB1〗0的时间序列延迟了约3 h。经修正时间延迟后,对磁层顶日下点距离〖WTB1X〗R0与磁暴D〖WTB1〗st指数的线性相关性进行分析。结果表明:发生超级磁暴时,二者线性相关系数的均值为077;大磁暴时,线性相关系数的均值为074;中等磁暴时,线性相关系数的均值为047。此外,用最小二乘数据拟合得到了不同级别磁暴时的〖WTB1X〗R0 D〖WTB1〗st关系图。     

Can we improve the spatial predictions of seabed sediments? A case study of spatial interpolation of mud content across the southwest Australian margin

Spatially continuous data of environmental variables is often required for marine conservation and management. However, information for environmental variables is usually collected by point sampling, particularly for the marine region. Thus, methods generating such spatially continuous data by using point samples to estimate values for unknown locations become essential tools. Such methods are, however, often data- or even variable-specific and it is difficult to select an appropriate method for any given dataset. In this study, 14 methods (37 sub-methods) are compared using samples of mud content with five levels of sample density across the southwest Australian margin. Bathymetry, distance-to-coast, slope and geomorphic province were used as secondary variables. Ten-fold cross validation with relative mean absolute error (RMAE) and visual examination were used to assess the performance of these methods. A total of 1850 prediction datasets are produced and used to assess the performance of the methods and the effects of other factors considered. Considering both the accuracy and the visual examination, we found that a combined method (i.e., random forest and ordinary kriging: RKrf) is the most robust method. This method is novel, with a RMAE up to 17% less than that of the control. No threshold in sample density was detected in relation to prediction accuracy. No consistent patterns are observed between the performance of the methods and data variation. The RMAE of three most accurate methods is about 30% lower than that of the best methods in previous publications, highlighting the robustness of the methods selected in this study. The implications and limitations of this study are discussed and a number of suggestions are provided for further studies.     

Neural network estimation of duration of strong ground motion using Japanese earthquake records

The duration of strong motion has a significant influence on the severity of ground shaking. In this work, a combination of average values of four geophysical properties of site (Standard Penetration Test (SPT) blow count, primary wave velocity, shear wave velocity, and density of soil) including hypocentral distance of less than 50 km and magnitudes more than 5.0 from Japanese ground motion records were used for development of neural network model, to estimate duration of strong ground motion. Since majority of strong motion databases provide only average shear wave velocity for site characterization, an attempt has also been made to train the neural network with magnitude, hypocentral distance and average shear wave velocity as three input variables. Results obtained from this study show that the duration of strong motion is mostly dependent on average shear wave velocity rather than other geophysical properties of site.     

Influence of ground motion spatial variation,site condition and SSI on the required separation distances of bridge structures to avoid seismic pounding

It is commonly understood that earthquake ground excitations at multiple supports of large dimensional structures are not the same. These ground motion spatial variations may significantly influence the structural responses. Similarly, the interaction between the foundation and the surrounding soil during earthquake shaking also affects the dynamic response of the structure. Most previous studies on ground motion spatial variation effects on structural responses neglected soil–structure interaction (SSI) effect. This paper studies the combined effects of ground motion spatial variation, local site amplification and SSI on bridge responses, and estimates the required separation distances that modular expansion joints must provide to avoid seismic pounding. It is an extension of a previous study (Earthquake Engng Struct. Dyn. 2010; 39 (3):303–323), in which combined ground motion spatial variation and local site amplification effects on bridge responses were investigated. The present paper focuses on the simultaneous effect of SSI and ground motion spatial variation on structural responses. The soil surrounding the pile foundation is modelled by frequency‐dependent springs and dashpots in the horizontal and rotational directions. The peak structural responses are estimated by using the standard random vibration method. The minimum total gap between two adjacent bridge decks or between bridge deck and adjacent abutment to prevent seismic pounding is estimated. Numerical results show that SSI significantly affects the structural responses, and cannot be neglected. Copyright © 2010 John Wiley & Sons, Ltd.     

乌鲁木齐王家沟断层组地表变形特征及强变形带宽度

王家沟断层组断错了中更新世砾石台地及王家沟东岸的Ⅲ级阶地,地貌形迹非常清晰,地表变形现象主要表现为地震断层、断层陡坎和挤压鼓包等。根据不同地貌面上跨断层测量获得的一系列实测数据,得到王家沟Ⅲ级阶地上的地表陡坎高度为0.4～1.6m,最大变形带宽度为50m左右; 中更新世台地上的陡坎高度多为1.5～5.0m,最大变形带宽度为90m左右。利用探槽开挖揭露出的断层位置与地表强变形带测量剖面的叠加对比,初步确定王家沟断层组上、下盘之间变形宽度的比例为2:1左右,并由此讨论了王家沟断层组上、下盘的 "避让带"宽度问题。     

利用变形河流阶地限定帕米尔北缘木什背斜的缩短、隆升和侧向扩展

位于帕米尔前缘逆冲推覆体(Pamir Front Thrust,PFT)东端的木什滑脱背斜,是帕米尔弧形推覆构造带最前缘和最新的变形带。对地形横剖面、纵剖面和水系发育特征的分析表明,木什背斜总体上具有由西向东扩展生长的特征。在背斜核部及北翼发育数级开阔平坦的沿轴向展布的河流阶地,阶地可划分为4期。利用阶地堆积细颗粒石英光释光测年获得阶地面T2a、T3和T4的形成年龄分别为(15.8±2.40)ka、(55.1±10.3)ka、(131.4±23.9)ka。伴随背斜的生长扩展,河流阶地面发生了横向和纵向掀斜,并形成断层陡坎和褶皱陡坎。木什背斜晚第四纪的缩短和隆升主要是通过褶皱翼旋转机制进行的,估算其最小缩短速率为(1.6±0.3)mm/a,最小隆升速率为(1.9±0.3)mm/a。与此同时,沿轴向背斜发生了向东的侧向迁移和旋转。根据背斜垂直隆升与侧向扩展之间的关系,估算背斜在131～16ka期间向东的侧向迁移扩展速率较快,为 (14.6±3.6)mm/a; 自16ka至今,侧向迁移扩展速率迅速减小至(1.7±0.3)mm/a,背斜向东的迁移扩展可能已基本停止,而以侧向旋转为主。     

珠江河口对外海潮波响应的固有频率研究——采用系统控制论方法

采用受控的自回归滑动平均模型(CARMA)分别研究了珠江河口洪、枯季对外海潮波响应的固有频率。枯季采用单输入单输出模型,洪季采用双输入单输出模型,通过验证、检验表明,模型(CARMA)可用于寻求复杂网河对外海潮波响应的固有频率,方法可靠,易操作。通过频率增益响应分析,发现枯季珠江河口的固有频率以浅水分潮频段为主,对应周期介于6~10.0 h之间,枯季固有频率未出现在全日潮波对应的频段。洪季珠江河口的固有频率也以浅水分潮频段为主,珠江河口对浅水分潮的系统增益响应幅值最大。固有频率接近浅水分潮频段的站点,枯季较洪季固有频率减小,对应周期延长。     

日本血吸虫毛蚴对不同密度和距离湖北钉螺易感性的初步实验观察

为探讨日本血吸虫（Schistosoma japonicum）毛蚴对不同密度、不同距离湖北钉螺（Oncomelania hupensis）易感性,在现场环境下,采用20000条新鲜孵化出的日本血吸虫毛蚴分别感染1、2、3、5m处的湖北钉螺,每处钉螺分为5、10、50、100只／袋4个密度组,感染4h后带回实验室饲养,8...     

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