回填土不确定性对场地地震反应的影响

选取某核电场地控制性钻孔的厚度、剪切波速、密度等实际勘探数据,通过改变回填土剪切波速,分析了回填土不确定性对场地地震动参数的影响。研究结果表明:在回填土层厚度不变和模型总厚度不变的情况下,地表的水平向峰值加速度随着回填土剪切波速的增大而减小,但水平向峰值加速度增幅逐渐减小;回填土剪切波速到达一定的波速就不再影响地表水平峰值加速度;随着回填土剪切波速的增加,整个反应谱的谱值都普遍减小。     

利用强震记录校正的芦山7.0级地震峰值加速度震动图

运用考虑场地效应的震动图快速生成方法,综合考虑震中地区地质构造背景、震源机制解结果及中国西部地区地震动参数衰减特征,估计了2013年4月20日芦山7.0级地震加速度分布图.利用地震后获得的强震记录计算了强震台站观测值与借助经验性衰减关系估计值之间的系统偏差,进一步修正了峰值加速度分布图.结果显示,由于芦山地震属于高角度逆冲型地震,加大了震区的震动程度,特别是震中附近30km范围内震动程度比校正前的结果更高.     

城市近地层湍流特征分析

利用中国科学院大气物理研究所在北京的325 m铁塔观测资料,本文分析了47、140和280 m三个高度的湍流统计特征.结果表明,城市近地层的湍流速度方差和湍流温度方差都较好地满足局地相似关系,140 m和280 m的湍流特征非常接近,而47 m的湍流特征与之相比表现出明显的差异,说明由于城市冠层动力和热力非均匀性的影响...     

The dependence of response spectrum on the tectonic ambient shear stress field

Introduction The acceleration response spectrum and peak ground acceleration are the necessary and im-portant parameters in earthquake-resistant design at present. They are still active research field. With the increase of digital high accurate strong motion observation data, especially the earth-quakes of Loma Prieta (M=7.0) in 1989; Landers (M=7.3) in 1992; Big Bear (M=6.4) in 1994 and Northridge (M=6.7) in 1994 in USA; Kozani (M=6.6) earthquake and afteshocks in 1995 in Greece; Dinar…     

潜在震源区震级上限对基岩加速度反应谱特征周期的影响

地震学理论和强震观测者表明,强震反应谱在形状主要取决于震级、震中距和场地条件。由于我国现行的各种行业建筑物抗震设计规范中对标准加速度反应谱特征周期Ｔｇ作出的规定中一般只考虑场地和震中距的影响或只考虑场地影响,因此在某些情况下,由规范所得到的反应谱特征周期与由专门的地震危险性分析所得到的结果相差较大。本文通过理论分析和实际的算例,讨论了潜在震源区震级上限对基岩加速度反应谱特征周期的影响。所得到的结论     

城市建筑动力学效应对对流边界层影响的敏感性试验

本文将大涡模拟应用于城市对流边界层(CBL)湍流结构和流场特征的研究,在大涡模式中,拖曳系数取与建筑物高度及建筑物高度标准差有关的表达式以考虑次网格建筑物对风速和湍流动能(TKE)的面积平均影响.模拟结果表明,由于城市建筑物对气流的拖曳作用,使建筑物冠层及整个CBL内风速大幅度减小,城市冠层内部风速减小尤为明显,在夹卷层内,风速有一明显的跃变.在边界层中部对流运动已经发展成为较强的热泡,城市建筑物的动力学效应使热泡的水平尺度增大,CBL内平均上升气流速度和下沉气流速度减小,同时使CBL中上升气流所占比例比平坦地面增大.城市建筑物使CBL低层热通量、动量通量、速度方差和位温方差明显增大,但对近地层高度以上的湍流量影响不大.     

Regular and chaotic dynamics in 3D reconnecting current sheets

We consider the possibility of particles being injected at the interior of a reconnecting current sheet (RCS), and study their orbits by dynamical systems methods. As an example we consider orbits in a 3D Harris type RCS. We find that, despite the presence of a strong electric field, a 'mirror' trapping effect persists, to a certain extent, for orbits with appropriate initial conditions within the sheet. The mirror effect is stronger for electrons than for protons. In summary, three types of orbits are distinguished: (i) chaotic orbits leading to escape by stochastic acceleration, (ii) regular orbits leading to escape along the field lines of the reconnecting magnetic component, and (iii) mirror-type regular orbits that are trapped in the sheet, making mirror oscillations. Dynamically, the latter orbits lie on a set of invariant KAM tori that occupy a considerable amount of the phase space of the motion of the particles. We also observe the phenomenon of 'stickiness', namely chaotic orbits that remain trapped in the sheet for a considerable time. A trapping domain, related to the boundary of mirror motions in velocity space, is calculated analytically. Analytical formulae are derived for the kinetic energy gain in regular or chaotic escaping orbits. The analytical results are compared with numerical simulations.     

Interstellar scintillation and clouds of the interstellar turbulent plasma

Data on interstellar diffraction and refraction scintillation of pulsars are analyzed. Comparison between theory and the observational data shows that two types of spectra for electron density fluctuations are realized in the interstellar medium: pure power law and piecewise with a break. The distribution of turbulent plasma in the Galaxy has a three component structure. Component A is diffuse and it is distributed outside of the spiral arms of the Galaxy. Component BI is cloudy and associated with Galactic arms. Component BII is extremely nonuniform and associated with HII regions and supernova remnants. The origin of the interstellar plasma turbulence is considered, and possible sources of turbulent energy are discussed. The contribution of supernova bursts in the interstellar gas ionization and generation of turbulence are analyzed among other factors. This revised version was published online in July 2006 with corrections to the Cover Date.     

On turbulence in the quasi-perpendicular bow shock

In this paper we propose to review the fundamental aspects of turbulence theories and their relevance to particle distribution functions observed by the cluster satellites in the quasi-perpendicular shock. The paper focusses on the hierarchical model describing the different levels of plasma turbulence; from the linear theory, through the quasi-linear remedy, to strong turbulence theories in the context of the earth's bow shock. We will discuss very briefly the validity of these approximations, and their relevance as far as satellite observations are concerned. In particular, we will discuss the development of non-Gaussian features in the ion distribution functions through the evaluation of higher order moments such as the kurtosis or flatness and the skewness. We have found that the profile of the kurtosis versus skewness tends to collapse to a parabolic line. This in turn allows us to draw analogies with neutral fluid turbulence where such a collapse of the kurtosis-skewness profile has been observed.