河套地震带的震源机制类型时空分布特征

基于地质构造背景分析,收集2000年以来发生在河套地震带的M_L≥2.8级地震作为研究对象,综合运用基于P波初动的振幅比方法(APAS)和基于波形拟合的CAP反演方法求出256次地震事件的震源机制解。以断层节面滑动角作为判定指标,分区域给出了河套地震带的震源机制类型空间和时间分布图像,从断层滑动角度呈现河套地震带应力场时空变化过程。结果显示:临河盆地断层节面滑动角主要在水平±20°方向存在优势分布,走滑型特征显著;具体来讲,狼山-色尔腾山山前断裂带、临河断裂、乌拉山山前断裂等主要以纯走滑型地震为主,巴彦乌拉山断裂与磴口-本井断裂之间的区域多分布正走滑型地震。呼包盆地断层节面解虽然也呈现出走滑型为主的特征,但滑动角分布较为离散,优势分布方向不明显;呼包盆地西侧的包头至西山咀凸起一带表现出以走滑为主的小范围震源应力场特征,呼包盆地内部及东侧由于显著的区域垂直差异运动,正断层和逆冲型地震所占比例较大,震源机制类型整体呈现出与构造相依的分布特点。分析认为,2000年以来,河套地震带的应力场存在一定的时空非均匀性变化,研究结果更多表现了河套地震带的震源应力场变化过程,而研究资料时间不够长和震级不够大是引起这种应力场非均匀性暂态特征的主要因素。     

Incremental dynamic analysis for estimating seismic performance sensitivity and uncertainty

Incremental dynamic analysis (IDA) is presented as a powerful tool to evaluate the variability in the seismic demand and capacity of non‐deterministic structural models, building upon existing methodologies of Monte Carlo simulation and approximate moment‐estimation. A nine‐story steel moment‐resisting frame is used as a testbed, employing parameterized moment‐rotation relationships with non‐deterministic quadrilinear backbones for the beam plastic‐hinges. The uncertain properties of the backbones include the yield moment, the post‐yield hardening ratio, the end‐of‐hardening rotation, the slope of the descending branch, the residual moment capacity and the ultimate rotation reached. IDA is employed to accurately assess the seismic performance of the model for any combination of the parameters by performing multiple nonlinear timehistory analyses for a suite of ground motion records. Sensitivity analyses on both the IDA and the static pushover level reveal the yield moment and the two rotational‐ductility parameters to be the most influential for the frame behavior. To propagate the parametric uncertainty to the actual seismic performance we employ (a) Monte Carlo simulation with latin hypercube sampling, (b) point‐estimate and (c) first‐order second‐moment techniques, thus offering competing methods that represent different compromises between speed and accuracy. The final results provide firm ground for challenging current assumptions in seismic guidelines on using a median‐parameter model to estimate the median seismic performance and employing the well‐known square‐root‐sum‐of‐squares rule to combine aleatory randomness and epistemic uncertainty. Copyright © 2009 John Wiley & Sons, Ltd.     

水平受荷长桩弹塑性计算解析解

当考虑桩侧土体非线性本构关系时对水平受荷桩的计算一般需采用数值方法,解析结果相对较少。基于Winkler地基模型和桩侧土体简化的弹塑性本构关系,对均质地基中水平荷载作用下桩头嵌固的长桩进行了解析推导,得到了桩身最大挠度及最大弯矩与荷载关系的统一解析表达式,并采用相同的方法求得高桩情形下桩头挠度的计算式。计算表明,联合荷载作用下桩身泥面处的挠度和转角不等于单个荷载作用时的线性叠加,采用常规的线性叠加法计算将偏于不安全。所求解析式借助计算器即可进行最大挠度和最大弯矩的计算,大大方便了工程的计算应用。     

一种冲击噪声中波达方向估计的有效算法

基于空间平滑技术和矩阵重构技术,提出了一种相干信源下波达方向估计的新算法。算法在非高斯冲击噪声下,能对波达方向进行有效地估计。与基于分数低阶矩算法以及基于分数低阶矩平滑算法相比较,新算法能在信噪比为-5dB时,提高40％的成功估计概率。信噪比为0dB-10dB时,成功概率大约提高20％,且均方根误差被降低近20％-50％。计算机仿真结果验证了算法的有效性。     

北天山西段中强地震应力触发作用初步研究

计算了新疆北天山西段1944年以来部分5级以上地震产生的静态库仑破裂应力变化(ΔCFS),分析该区先发生的中强震产生的累加库仑应力变化以及单个中强地震对后续地震的触发作用。研究中依据静态库仑破裂应力变化的空间分布确定后续地震活动的可能增强区范围,应用累积贝尼奥夫应变研究增强区内中等地震活动的加速矩释放特征,定量论证中强震产生的库仑应力变化对后续地震产生的影响的可靠性。结果表明,北天山西段多数中强震产生的ΔCFS有利于其邻区后续中强震的发生,其中正ΔCFS区是后续中强地震的可能发生地点,该区中强震产生的库仑应力变化作用的时空影响范围分别为几天至几十年1、00 km范围内,这为未来地震趋势判定提供了依据。     

1999年四川绵竹5.0级地震临震电磁辐射信号的准-静电磁场场强理论估算

1999年9月14日和11月30日在四川省绵竹县清平乡和汉源乡先后发生Ms5.0地震.本文通过都江堰电磁波ULF超低频观测仪震前接收到的电磁辐射信号,对观测场量的某些特征进行理论分析和估算.结果表明:理论估算是针对地下发射、空中接收的方式进行的,且针对ULF频段的磁场,与地下发射-地下接收方式的ULF频段的电场所计算的对比结果表明,此估算结果是合理的;两次地震辐射源峰值电流矩为108～106 A·m量级(平均为107A·m量级),表明两次地震的孕震体与孕震过程可能不是"独立"的.     

Assessment of cyclic response to suction caisson in clay using a three-dimensional displacement approach

An investigation was made to present analytical solutions of cyclic response to suction caisson subjected to inclined cyclic loadings in clay using a three-dimensional displacement approach. A model representing the relationship between vertical load and vertical displacement and that between lateral load and lateral displacement along the skirt of suction caisson subjected to cyclic loadings is proposed for overconsolidated clay. For the effect of vertical load on cyclic load capacity of suction caisson, using the Mindlin solution in the case of a vertical point load, the vertical stress of soil under the base of suction caisson is presented. For the stress state of soil beneath the base of suction caisson subjected to cyclic loading, the Mohr–Coulomb failure line and critical state line are presented and the relationship between total stress, effective mean principal stress, stress difference, and pore-pressure is elucidated. The comparison of results predicted by the present method for a suction caisson subjected to cyclic loadings in clay has shown good agreement with those obtained from field tests. Cyclic behavior of clay up to failure is made clear from the relationship between cyclic tensile load, vertical and lateral displacements, and rotation and that between depth, vertical, and lateral pressures.     

三轴刚性地球自由旋转欧拉角变化数值模拟研究

假定地球是一个三轴刚性体,在Euclid空间中做自由旋转.在设定主惯性矩A小于B小于C的情况下,求解欧拉运动方程,得到数值解.计算结果表明:地球在除了自转和自由进动之外,同时还存在着自由章动.章动角会随着时间做周期性变化.重点讨论的是章动角的变化.     

直线特征标志子像素级定位方法的研究

在近景摄影测量中,常常需要对直线特征的标志进行定位,而标志定位的精度会影响到整个测量的精度。提出一种新的混合方法,即采用Hough变换对直线特征标志进行直线检测,得到直线初值;然后采用灰度矩边缘直线拟合定位法,对标志点中心进行子像素定位。在三维重建实验中采用所提出的灰度矩边缘直线拟合定位法和高精度直线定位法进行精度比较,实验证明经过Hough变换得到粗值的灰度矩边缘直线拟合定位法达到较高的定位精度,且计算更简单。     

GRACE’s implication of temporal inertia moment and length of day

This paper aims to study the Earth’s temporal inertia moment and its influence on length of day (LOD). First, the GRACE data are processed by wavelet analysis to remove abnormal jumps and noises. Then the theoretical impacts of the second-order potential coefficients on the inertia moment and LOD are studied. Finally, the processed GRACE data are applied and results show that mass redistribution has led to decreasing tendencies of inertia moment and LOD as well as some unexpected seasonal oscillations in the recent 6 years. Supported by the Open Fund of Key Laboratory of Geospace Environment and Geodesy, Ministry of Education, China (No.08-02-02), the Special Project Fund of State Key Laboratory of Information Engineering in Surveying, Mapping and Remote Sensing (China), the National 863 Program of China (No.2006AA12Z211).