Source parameters of the 2004 Kaliningrad earthquakes

An analysis of source parameters of the two unexpected earthquakes from the Kaliningrad (Russia) area is presented. The earthquakes occurred on 21 September 2004 at 11:05:01 and 13:32:31 UT, respectively. The first event was located at the latitude φ = 54.924°N and the longitude λ = 20.120°E, with a depth h = 16 km, and the second event at φ = 54.876°N, λ = 20.120°E and h = 20 km. Magnitudes Mw of the two events were very similar: 5.1 and 5.2. The magnitude values reported by various international data centers have been meaningfully different. The reason is the presence of high-frequency components in Z velocity component of the S wavefield. They were observed along the direction defined by two stations, BLEU in Sweden and SUW in Poland, located in opposite sides of the source. Along the direction perpendicular to it, the effects are relatively very small. The high-frequency waves are understood to mean components in the 6–8 Hz band for event 1 and 2-4 Hz for event 2. The effects in question are also clearly visible on displacement spectrograms. The magnitude values calculated at such stations from S-wave amplitudes or from seismic spectra are clearly overestimated and are close to 6. Therefore, we made a careful selection of channels in order to determine the spectral parameters and, on this basis, the source parameters. The size of the source is relatively small, of about 2 km. The closest seismic station is at 100 source radii from the source. One can clearly see the effect of the TT zone which markedly reduces the seismic moment value for seismic stations laying on the opposite sides of the source. Both events have very similar spatial distributions of the source parameters: magnitude, seismic moment and radius.     

蒲石河抽水蓄能电站上水库裂隙岩体渗透张量的确定

本文提出了一种既能反映裂隙岩体的渗透特性,又相对准确的确定裂隙岩体渗透张量的方法。首先通过裂隙在空间展布状况的测量,用统计学方法初步确定裂隙岩体的渗透张量,获得渗透主值及主方向,然后根据野外压水试验得到的岩体透水率,利用巴布什金公式计算各试段岩体的渗透系数,求出修正系数,从而得到研究区裂隙岩体的修正渗透张量。并运用上述方法对蒲石河抽水蓄能电站上水库坝址区裂隙岩体的渗透张量进行了计算。结果表明,该方法能较好地刻画裂隙岩体渗透性的各向异性特征,可为岩体渗透性分区及防渗帷幕的优化提供科学依据。     

Stochastic partial differential equations in groundwater hydrology

Many problems in hydraulics and hydrology are described by linear, time dependent partial differential equations, linearity being, of course, an assumption based on necessity.Solutions to such equations have been obtained in the past based purely on deterministic consideration. The derivation of such a solution requires that the initial conditions, the boundary conditions, and the parameters contained within the equations be stipulated in exact terms. It is obvious that the solution so derived is a function of these specified, values.There are at least four ways in which randomness enters the problem. i) the random initial value problem; ii) the random boundary value problem; iii) the random forcing problem when the non-homogeneous part becomes random and iv) the random parameter problem.Such randomness is inherent in the environment surrounding the system, the environment being endowed with a large number of degrees of freedom.This paper considers the problem of groundwater flow in a phreatic aquifer fed by rainfall. The goveming equations are linear second order partial differential equations. Explicit form solutions to this randomly forced equation have been derived in well defined regular boundaries. The paper also provides a derivation of low order moment equations. It contains a discussion on the parameter estimation problem for stochastic partial differential equations.     

Implications of principal stress axes and eigenvalue ratios on critical orientation of fractures. Application to two tectonic regions in Alaska

The principal stress axes and eigenvalue ratios of the stress tensors from two active seismic regions in Alaska (eastern Aleutian Arc and eastern Gulf of Alaska) are computed. These results are obtained using focal mechanisms of earthquakes with magnitudes ranging from 5.5 to 8.2 and show for both regions slightly different compressional states with an orientation of the pressure axis of N26°W for the eastern Gulf of Alaska and N27°W for the east Aleutian Arc. The eigenvalue ratios for the eastern Gulf of Alaska and east Aleutian Arc are 0.84 and 0.99, respectively. The algorithm used in computations allows us to detect some focal mechanisms which are incoherent with respect to the obtained stress tensors. These incoherences are explained in terms of some tectonic features of the region. The orientations of possible pre-existing fractures which would need an unrealistically high maximum shear stress to start a slip on their fault planes are also investigated. These critical orientations depend on a constitutive frictional law as well as on eigenvalue ratios and eigenvectors of the stress tensors. The orientation, which is given in our case by the angle between the normal vector to a fracture and the regional tensional axis, is approximately 59° for the eastern Aleutian Arc. This angle ranges from 49° to 59° for the eastern Gulf of Alaska. It must be pointed out that fractures which need unrealistically high shear stress to start slip on their fault planes are defined by a very narrow band of possible angles between tensional direction and the normal vector to fault plane.     

河北唐山地区中小地震震源参数的测定

采用谱分析的方法，利用首都圈数字遥测地震台网的观测资料，计算了唐山地区2002年ML2．0以上的58个中小地震的波谱，进而估算了地震矩、拐角频率、应力降、震源破裂半径，并讨论了它们之间的相互关系以及拐角频率和应力降的时间分布特征。分析表明，地震矩与震级、拐角频率与震级的关系密切，证实结果可信、稳定。     

矩、概率权重矩与线性矩的关系分析

本文叙述了矩、概率权重矩与线性矩之间的关系，并以Г分布为例进行分析。线性矩的计算式为概率权重矩的线性组合，两者的计算结果完全相同。概率权重矩和线性矩均与指定的频率分布型式和作为权重的概率有关，结果的敏感性较差。详细分析了计算参数的近似公式及其精度。对水文应用而言，它们的计算结果仅是估计的初值，需经过合理性分析才能取用。     

利用数字地震记录的,振幅比资料测定小震震源机制解的可靠性分析

震源机制解的可靠性越来越受到人们的重视 ,已有的检验工作证实中国早期或者手工作图测定的震源机制解可靠性极差。经比较 ,由远震波形反演的矩张量解 ,同一地震不同作者的结果之间差异甚小 ,可靠性较高 ;而基于P波初动方向测定震源机制解的格点尝试法所给出的解空间比其他方法要好。对 2 0 0 3年 4月发生在首都圈数字化地震台网范围内的 2次 4级地震进行了分析。取用不同的资料 ,由格点尝试法和 -P ,-S垂直向振幅比方法分别测定了震源机制解 ,二者基本一致 ,并且和过去当地发生的 5级以上地震的哈佛大学CMT解接近。这既说明了地震活动的继承性 ,也证实了震源机制解并非随机分布。由于中小地震发生的随机性 ,用统计的方法对用振幅比资料测定的震源机制解进行分析 ,结果是客观、恰当的     

地球物质的人为转移与地球物理环境

通过分析航天活动向外层空间迁移物质形成的地球转动惯量改变,重叠1998年以来,从高纬度向赤道方向上,巨大物质发生再分布构成的地球转动惯量改变,和它们致使地球自转速率的变慢,重合地球自转运动的规律性变慢,以叠加的效果影响地球物理环境;以及与地壳差速旋转的巨大地核,及覆盖地表的水,包裹地球的大气层,在地壳转速变化时,完成其相互问角动量交换存在的时间滞后性,将会在一些瞬时段突出物质转移对地球物理环境的作用影响.讨论航天发射从地球迁移到外层空间的物质,正将形成一定规模的物质群而改变地球系统的空间结构,且现时,太空武器化竞争已剑拔弩张,其一旦加剧了航天活动构成外层空间新物质体系圈层的发展,其过程对地球物理环境的影响,合并地球自身多重因素的作用,可能会增大突破维持稳定自然环境的某些临界条件的几率和增大突发事件发生频率.     

STUDY OF THE RELATIONSHIP BETWEEN IWC AND Z FOR NONSPHERICAL ICE PARTICLES AT MILLIMETER WAVELENGTH

Ice water content (IWC) plays important roles in weather and climate change. Determining the IWCs of cirrus clouds with millimeter-wavelength radar can be problematic due to influences of ice particle rotation on their backscattering cross sections. We here introduce models to describe the radiation patterns of six nonspherical particles of specific sizes. Simulations using HFSS software were applied to describe the differences resulting from different orientations and equivalent spheres. A double exponential function was used for fitting to describe the relationship between the particles’ maximum sizes and backscattering cross sections. The backscattering cross sections of nonspherical ice particles were computed by the method of moment, and those of the equivalent spherical particles were computed by Lorenz-Mie theory for three different orientations: fixed, horizontal, and random. Assuming that a mixture of nonspherical ice particles follows the B-H mixing model, the size distribution of cirrus particles obeys the exponential distribution measured by NASA in 2007. By computing the IWCs of cirrus clouds, which follows the above mentioned B-H model and exponential distribution, the radar reflectivity factors of nonspherical ice particles and equivalent spheres at three different orientations can be computed. Subsequently, the IWC results can be acquired by inputting the radar reflectivity variables into the well-known IWC-Z formula. The analysis described here demonstrates that when using the radar reflectivity Z, the orientation must be considered in order to determine the IWC. Using equivalent sphere theory, the derived IWCs underestimate the actual IWCs. These results are important for accurately retrieving the microphysical parameters of cirrus clouds.     

Case studies of damage to 19‐storey irregular steel moment‐frame buildings under near‐source ground motion

This paper describes the three‐dimensional nonlinear analysis of six 19‐storey steel moment‐frame buildings, designed per the 1997 Uniform Building Code, under strong ground motion records from near‐source earthquakes with magnitudes in the range of 6.7–7.3. Three of these buildings possess a reentrant corner irregularity, while the remaining three possess a torsional plan irregularity. The records create drift demands of the order of 0.05 and plastic rotation demands of the order of 4–5% of a radian in the buildings with reentrant corners. These values point to performance at or near ‘Collapse Prevention’. Twisting in the torsionally sensitive buildings causes the plastic rotations on the moment frame on one face of the building (4–5% of a radian) to be as high as twice of that on the opposite face (2–3% of a radian). The asymmetric yield pattern implies a lower redundancy in the lateral force‐resisting system as the failure of the heavily loaded frame could result in a total loss of resistance to torsion. Copyright © 2006 John Wiley & Sons, Ltd.