Failure modes and bearing capacity of strip footings on soft ground reinforced by floating stone columns

This study evaluates the failure modes and the bearing capacity of soft ground reinforced by a group of floating stone columns. A finite difference method was adopted to analyze the performance of reinforced ground under strip footings subjected to a vertical load. The investigation was carried out by varying the aspect ratio of the reinforced zone, the area replacement ratio, and the surface surcharge. General shear failure of the reinforced ground was investigated numerically without the surcharge. The results show the existence of an effective length of the columns for the bearing capacity factors N _c and N _γ. When certain surcharge was applied, the failure mode of the reinforced ground changed from the general shear failure to the block failure. The aspect ratio of the reinforced zone and the area replacement ratio also contributed to this failure mode transition. A counterintuitive trend of the bearing capacity factor N _q can be justified with a shift in the critical failure mode. An upper-bound limit method based on the general shear failure mode was presented, and the results agree well with those of the previous studies of reinforced ground. Equivalent properties based on the area-weighted average of the stone columns and clay parameters were used to convert the individual column model to an equivalent area model. The numerical model produced reasonable equivalent properties. Finally, a theoretical method based on the comparison of the analytical equations for different failure modes was developed for engineering design. Good agreement was found between the theoretical and numerical results for the critical failure mode and its corresponding bearing capacity factors.     

南黄海及沿岸地震活动时空动态扫描特征

从中强震成组孕育出发,研究了南黄海及沿岸地区地震活动时空动态图象扫描特征,探索了该区地震危险性预测的有关问题。结果表明,该区２０多年来４级地震活动总休上呈相对平稳状态,但在不同时段则出现不断演变迁移的４级地震局部集中区及低ｂ值区等异常区域,５～６级中强地震大都发生于异常区的边中附近;异区内４级地震累积频度往往呈非线性指数加速,中强震发生于４级地震非线性指数加速的后期或其后的异常平静期中。这种地震活     

Curvelet reconstruction of non-uniformly sampled seismic data using the linearized Bregman method

Seismic data reconstruction, as a preconditioning process, is critical to the performance of subsequent data and imaging processing tasks. Often, seismic data are sparsely and non-uniformly sampled due to limitations of economic costs and field conditions. However, most reconstruction processing algorithms are designed for the ideal case of uniformly sampled data. In this paper, we propose the non-equispaced fast discrete curvelet transform-based three-dimensional reconstruction method that can handle and interpolate non-uniformly sampled data effectively along two spatial coordinates. In the procedure, the three-dimensional seismic data sets are organized in a sequence of two-dimensional time slices along the source–receiver domain. By introducing the two-dimensional non-equispaced fast Fourier transform in the conventional fast discrete curvelet transform, we formulate an L1 sparsity regularized problem to invert for the uniformly sampled curvelet coefficients from the non-uniformly sampled data. In order to improve the inversion algorithm efficiency, we employ the linearized Bregman method to solve the L1-norm minimization problem. Once the uniform curvelet coefficients are obtained, uniformly sampled three-dimensional seismic data can be reconstructed via the conventional inverse curvelet transform. The reconstructed results using both synthetic and real data demonstrate that the proposed method can reconstruct not only non-uniformly sampled and aliased data with missing traces, but also the subset of observed data on a non-uniform grid to a specified uniform grid along two spatial coordinates. Also, the results show that the simple linearized Bregman method is superior to the complex spectral projected gradient for L1 norm method in terms of reconstruction accuracy.     

不同Legendre函数递推公式对计算球谐函数定积分的影响

针对球谐函数定积分计算中Legendre函数递推问题展开研究,分析了标准向前列推法、Belikov法、跨阶次法、X数法以及顾及麦克劳林级数展开式对球谐函数定积分计算的影响。利用Eigen6c-4地球重力场模型计算扰动引力梯度径向分量,分析不同方法之间的差异。实验表明,不考虑麦克劳林级数展开式时4种方法的相对精度在高纬度地区较差,但计算模型扰动引力径向分量的精度一致,结合麦克劳林级数式可提高高纬度地区定积分计算的相对精度,但会降低中低纬度地区定积分计算的精度,并且对高纬度地区扰动引力径向分量的影响极小,但会严重降低低纬度地区扰动引力梯度计算的精度。     

CINRAD/SA雷达冰雹探测算法效果检验及参数本地化

2004年CINRAD/SA雷达新的冰雹探测算法(HDA)代替了原来的算法,新的冰雹探测算法(HDA)估测任意尺寸的冰雹概率(POH)、直径大于等于19 mm的强冰雹概率(POSH)和最大冰雹直径预测(MEHS)。结合济南雷达探测资料对冰雹探测算法预测效果进行了检验,虽然有较高的探测准确率,但同时错误率较高,临界成功率较低,最大冰雹尺寸预测值与实况的平均差值约为14.6 mm。对2002~2005年济南雷达站的历史资料进行了统计分析,降雹单体和非降雹单体在最大反射率因子上存在较大差异,5、6、7月的降雹单体最大反射率因子平均值分别为59.7、61.86、3.9 dBz,非降雹单体最大反射率因子平均值分别为53.8、54.9、55.6 dBz。依据统计数据,对冰雹探测算法中的反射率因子等门限值调整为53 dBz后,冰雹预测仍具有较高的探测准确率,错误率和临界成功率得到了明显改善;对最大冰雹尺寸预测中的算法因子门限值调整后,预测值与实况有较好的对应关系。     

Difference between focal mechanisms of Dayao earthquake doublet sequence

Using the maximum amplitude ratios of vertical component of P and S waves recorded by a regional network, 921 focal mechanisms of Dayao earthquake doublet sequence are determined by means of synthetic seismograms of a point source of dislocation in a plane layered medium.Among them,389 focal mechanisms are in the aftershock sequence of M6.2 earthquake occurred on 21 July,2003 and the other 532 focal mechanisms are in the aftershock sequence of M6.1 earthquake occurred on 16 October,2003 in Dayao,Yunnan.The ...     

Fault plane parameters of Tancheng M8? earthquake on the basis of present-day seismological data

The great Tancheng earthquake of M8? occurred in 1668 was the largest seismic event ever recorded in history in eastern China. This study determines the fault geometry of this earthquake by inverting seismological data of present-day moderate-small earthquakes in the focal area. We relocated those earthquakes with the double-difference method and found focal mechanism solutions using gird test method. The inversion results are as follows: the strike is 21.6°, the dip angle is 89.5°, the slip angle is 170°, the fault length is about 160 km, the lower-boundary depth is about 32 km and the buried depth of upper boundary is about 4 km. This shows that the seismic fault is a NNE-trending upright right-lateral strike-slip fault and has cut through the crust. Moreover, the surface seismic fault, intensity distribution of the earthquake, earthquake-depth distribution and seismic-wave velocity profile in the focal area all verified our study result.

     

青藏高原东缘汶川地震断层陡坎类型与级联破裂模型(英文)

The post-earthquake field investigations reveal that the MW7.9 Wenchuan earthquake of 12th May 2008 ruptured three NE-striking imbricate reverse faults and another NW-trending reverse fault, along the middle Longmenshan fold-and-thrust belt at the eastern margin of the Tibetan plateau.     

利用GPS观测反演Tokachi-Oki地震(日本)及强余震的同震滑移分布

根据GPS观测的Tokachi-Oki地震及强余震引起的地表位移,采用基于敏感性探测的方法反演了两次地震分别引起的断层滑移。反演过程中,考虑了更切合实际的分层地球模型和断层面几何形状。主震和强余震滑移量的最大值分别为3.07m和0.33m,相应的矩震级分别为Mw7.94和Mw7.1,与地震波形反演的结果基本一致。另外,从主震和强余震的滑移分布来看,强余震的滑移主要分布在主震破裂较小的区域,一种合理的解释是,主震的破裂过程增加了邻区断层面上的能量积累,导致了强余震的发生。     

东昆仑断裂的震后粘弹性松弛效应对地壳变形的影响

通过构建粘弹变形模型,对东昆仑断裂带附近近百年来发生的6个M≥7地震的震后粘弹性松弛效应进行数值模拟,分析该效应对区域地壳变形的影响。结果表明： 1) 离逝时间较短的1997年玛尼7.5级地震和2001年昆仑山口西8.1级地震造成的震后松弛效应对现今地壳变形的影响最为显著,在2次地震发生10~20 a后(2010~2020年)仍能造成最大约7.6 mm/a的地壳变形,跨断层变形速率最大约8.4 mm/a; 2) 2021年玛多7.4级地震震后粘弹效应在未来10 a内(2021~2030年)预计能造成最大约3.9 mm/a的地壳变形,2025~2030年跨断层变形速率可达2.6 mm/a。模拟结果表明,强震的震后粘弹性松弛效应对长期地壳变形和相关断层参数反演的影响不容忽视; 3) 考虑震后粘弹性松弛效应,采用跨断层GPS速度剖面反演的东昆仑断裂中段的滑移速率与地质学研究结果具有更好的一致性,若不考虑震后粘弹性松弛效应,则会明显高估30%的断层滑移率。