粘弹性介质中的地震波

给出了三元件的标准线性粘弹性固体在半平面内传播的地震波的解析解，它是由已知的弹性半平面内的解析解迭粘滞性解而得，从而克服了视地壳为二元件粘弹性体的Voigt模型或Maxell模型的缺点。     

Stability condition of finite difference solution for viscoelastic wave equations

The stability problem is a very important aspect in seismic wave numerical modeling. Based on the theory of seismic waves and constitutive equations of viscoelastic models, the stability problems of finite difference scheme for KelvinVoigt and Maxwell models with rectangular grids are analyzed. Expressions of stability conditions with arbitrary spatial accuracies for two viscoelastic models are derived. With approximation of quality factor Q≥?5, simplified expressions are developed and some numerical models are given to verify the validity of the corresponding theoretical results. Then this paper summarizes the influences of seismic wave velocity, frequency, size of grid and difference coefficients, as well as quality factor on stability condition. Finally the prerequisite conditions of the simplified stability equations are given with error analysis.     

Seismic isolation effect of lined circular tunnels with damping treatments

The Havriliak-Negami model for dynamic viscoelastic material behavior and Biot＇s theory of poroelasticity are employed to develop an exact solution for three-dimensional scattering effect of harmonic plane P-SV waves from a circular cavity lined with a multilayered fluid-filled shell of infinite length containing viscoelastic damping materials and embedded within a fluid-saturated permeable surrounding soil medium. The analytical results are illustrated with numerical examples where the effects of liner/coating structural arrangement, viscoelastic material properties, liner-soil interface bonding condition, seismic excitation frequency, and angle of incidence on the induced dynamic stress concentrations are evaluated and discussed to obtain representative values of the parameters that characterize the system. It is demonstrated that incorporating viscoelastic damping materials with a low shear modulus in the constrained layer configuration is an efficient means of enhancing the overall seismic isolation performance, especially for near-normally incident seismic shear waves where the amplitudes of induced dynamic stresses may be reduced by up to one-third of those without isolation in a relatively wide frequency range. Some additional cases are considered and good agreements with solutions available in the literature are obtained.     

Calculation method of prestack FAGVO and its applications

Frequency attenuation occurs when seismic waves propagate through the porous reservoirs containing hydrocarbons. Current researches on the seismic frequency attenuation mainly focus on the post-stack domain instead of the prestack domain. Here we propose the frequency attenuation gradient vs. offset (FAGVO) based on the amplitude variation with offset and frequency attenuation integral equations. We derive the FAGVO equation that equals to zero in a full-elastic medium and is negative in a viscoelastic medium. FAGVO is affected by the viscosity of the medium, the coefficients of reflection, the frequency variation, and high-frequency attenuation. FAGVO uses the differences of partially stacked data to decrease the interference caused by subsurface strata affecting the frequency attenuation, highlights the frequency attenuation gradient anomalies in hydrocarbon-bearing reservoir pores, and finally realizes the hydrocarbon fluid identification. The method was verified using a two-dimensional wave equation forward model and was found to be cost effective. Furthermore, the method does not require well information, which can be applied in the stage of seismic exploration, especially, in the exploration of a none-well project.     

黏弹介质波动方程有限差分解的稳定性研究

稳定性问题是地震波数值模拟的一个重要问题.基于地震波传播理论,从黏弹介质本构方程出发,对矩形网格下不同黏弹模型波动方程有限差分解的稳定性进行了理论分析,导出了Kelvin-Voigt黏弹模型和Maxwell黏弹模型在任意空间差分精度下稳定性条件的表达式;给出了品质因子Q≥5时的简化式,并通过数值算例验证了理论研究结论的正确性;总结了地震波速度、频率、空间网格大小、差分系数以及品质因子与稳定性条件的关系;通过误差分析给出了近似公式的使用条件.     

Seismic waves from large explosions reveal periodical deformations at lithospheric depths

Seismic signals from large explosions recorded by Soviet seismic stations in the distance range from 100 to 2800 km during 12–14 years are analysed. Periodic variations of travel times and amplitudes of P and S waves corresponding to different boundaries in the lithosphere have been discovered. Characteristic periods are close to 2 and 6 years. Since the variations of amplitudes and velocities of seismic waves may be caused by dilatational deformations of rocks, the results obtained reveal a possible existence of slow tectonic stress waves. Tectonic waves were detected not only at seismically active zones but also at aseismic regions of the Russian and Kazakh platforms. At almost all seismic stations these variations increase with the seismic ray depth in the lithosphere. This increase can be explained by the presence of bending deformations and by their attenuation due to the rheological stratification of the lithosphere. Accordingly, the theory of Elsasser's waves is generalized to include bending deformations and the presence of stationary asthenosphere flows.     

Soil-structure interaction with Rayleigh waves

Presented is a plane-strain method for soil-structure interaction analysis consisting of the superposition of the free field motions and the interaction motions in a generalized seismic environment. The free field is modelled as a horizontally layered viscoelastic medium and the seismic environment may consist of a combination of S, P and Rayleigh waves. The soil-structure system is modelled with viscoelastic finite elements, transmitting boundaries, viscous boundaries and a three-dimensional simulation. Comparative analyses of the same structure are conducted for an input of R waves and for vertically propagating S and P waves in a rock site and sand site. In the rock site the R waves produce higher peak horizontal spectral acceleration up to 25 per cent, and a significant rocking effect at points away from the centre of gravity of the structure. However, the S and P waves show higher peak vertical spectral acceleration by up to 15 per cent at the centre of the structure. Very similar horizontal response, but higher vertical response only at the centre of the structure for S and P waves, is obtained for the sand site.     

各向异性衰减薄层地震响应特征研究

薄储层的叠前地震响应特征研究,特别是针对具有速度各向异性的含流体薄层,对储层描述具有十分重要的意义.文中基于波动方程数值模拟方法,正演得到各向同性弹性、各向同性衰减、速度各向异性、各向异性衰减模型的地震波场,并对比分析了四种模型的纵波(PP)和转换横波(PS)地震反射特征.研究结果表明:在衰减介质背景下,引入各向异性,PP和PS波的反射波振幅较弹性介质均减弱,且衰减因素对薄层振幅的影响强于各向异性.同时,VTI各向异性衰减在单频PS振幅曲线上表现出强差异性,而HTI各向异性衰减则会影响PP和PS波单频振幅曲线的极值点幅值和位置,通过分析单频振幅曲线的极值点振幅和极值点位置对各向异性衰减薄层预测有指导作用,尤其对平时较难分辨的VTI各向异性衰减薄层,单频分析方法的优势更明显.     

Wave dispersion in dry granular materials by the distinct element method

Numerical studies are conducted to investigate the existence of wave dispersion in resonant column tests on dry granular soil. To this end, the two-dimensional distinct element method (DEM) in the time domain is employed. The investigations focus on the effect of sample width, voids ratio, viscous damping and wavelength, on propagation velocities of longitudinal harmonic waves in rectangular samples of uniform grains. It is shown that granular materials may exhibit anomalous dispersion that is, wave velocities that increase with increasing excitation frequency. This increase may exceed 20% for squatty samples, but becomes less pronounced for slender samples. Similar findings have been reported in some experiments on granular materials, but have not been systematically explored by numerical means. Results are presented in the form of dimensionless graphs and charts that elucidate the salient features of the problem. Comparisons with findings from gradient elastodynamic and viscoelastic theories are discussed.     

粘弹性介质中地震体波Q值的测定方法

本文以常用的几种粘弹性体模拟地球介质的粘弹性,建立了该种介质中的波动方程组;在运用合理的近似处理方法基础上,得到了基本解;提出了校正其它衰减因素的功率谱切比雪夫拟合方法,由此给出了粘性Q值的概念和算法,最后讨论了该方法的可行性。     

Mantle Convection Modeling with Viscoelastic/Brittle Lithosphere: Numerical Methodology and Plate Tectonic Modeling

--The earth's tectonic plates are strong, viscoelastic shells which make up the outermost part of a thermally convecting, predominantly viscous layer. Brittle failure of the lithosphere occurs when stresses are high. In order to build a realistic simulation of the planet's evolution, the complete viscoelastic/brittle convection system needs to be considered. A particle-in-cell finite element method is demonstrated which can simulate very large deformation viscoelasticity with a strain-dependent yield stress. This is applied to a plate-deformation problem. Numerical accuracy is demonstrated relative to analytic benchmarks, and the characteristics of the method are discussed.     

基于负刚度装置的超长联大跨连续梁桥地震反应控制研究

为完善超长联大跨连续梁桥的减、隔震技术,将负刚度装置引入到超长联大跨隔震连续梁桥中组成新型减、隔震系统,并与黏滞阻尼器-摩擦摆支座组合减震系统进行比较。基于CSiBridge软件建立全桥有限元模型,负刚度装置采用弹性多段线模拟,摩擦摆支座采用双线性恢复力模型,黏滞阻尼器采用Maxwell模型,输入3条地震波进行非线性时程分析,考查两种新型减、隔震系统下桥梁结构的地震反应,探究负刚度系统及黏滞阻尼器系统对超长联大跨连续梁桥地震反应的控制效果。研究结果表明：负刚度装置与黏滞阻尼器均可以有效地减小超长联大跨隔震连续梁桥的支座位移。负刚度装置对桥墩内力反应及梁体加速度反应的控制优于黏滞阻尼器。负刚度装置在超长联大跨连续梁桥地震反应控制中有较好的应用前景。     

Evaluation of stresses in two geodynamically different areas: Stable foreland and extensional backarc

Areas which are geodynamically different have different behaviors both in their thermal regime and seismic activity. A stable area has a geotherm which can be considered as standard, extensional and compressional areas have, respectively, high and low temperature gradients. The Italian region includes different geodynamical areas and all such situations are present. We consider the Apulian platform as an example of a stable area and the Tuscany-Latium as an example of an extensional area. For both of them the present geotherms are calculated, taking into account, for the Tuscany-Latium, its thermal history. Assuming that each region is subject to a constant strain rate, the stresses are calculated as functions of depth and time. The rheological behavior is assumed to be linear viscoelastic, with viscosity dependent on temperature and elastic parameters dependent on lithology. The geothermal profile and the rheological structure of the lithosphere remarkably affect the processes of stress accumulation which control the distribution of seismic activity. The abrupt decrease of the temperature gradient at the Moho produces considerably higher stress values with respect to the case of uniform gradient, thus favoring subcrustal seismicity. In the case of a standard temperature gradient, subcrustal seismicity is predicted and a gap in seismicity, indicating a soft intracrustal layer, exists if there is a discontinuity in rheology. By contrast, in the case of a high-temperature gradient, subcrustal seismicity is not to be expected, even in the presence of a discontinuity in rheology, since subcrustal temperatures are already too high to permit a sufficient stress accumluation.     

A method of calculating the non‐linear seismic response of a building braced with viscoelastic dampers

Buildings are continually subject to dynamic loads, such as wind load, seismic ground motion, and even the load from internal utility machines. The recent trend of constructing more flexible high‐rise buildings underscores the importance of including viscoelastic dampers in building designs. Viscoelastic dampers are used to control the dynamic response of a building. If the seismic design is based only on the linear response spectrum, considerable error may occur when calculating the seismic response of a building; rubber viscoelastic dampers show non‐linear hysteretic damping that is quite different from viscous damping. This study generated a non‐linear response spectrum using a non‐linear oscillator model to simulate a building with viscoelastic dampers installed. The parameters used in the non‐linear damper model were obtained experimentally from dynamic loading tests. The results show that viscoelastic dampers effectively reduce the seismic displacement response of a structure, but transmit more seismic force to the structure, which essentially increases its seismic acceleration response. Copyright © 2003 John Wiley & Sons, Ltd.     

地球动力学过程中的波动现象及其在地震预报中的应用

讨论了地球内部的波动现象与构造及地震间的关系。引进了４类广义构造波。它们是：表现为地球不同年代的综合构造运动结果的超长周期构造波；由地震活动性迁移，即所谓地震活动波所反映的长周期（不同类型与不同速度的，周期从几年到几十年）构造波；由地震前兆三阶段发展过程反映出的中等周期（从几月到几年）构造波；以及由地下水位、地倾斜、重力、地震波、电磁辐射、地声等的变化所记录的短周期（从几分到几天）构造波。地震活动波又有３类，可分别用广义瑞利型构造波、广义洛夫型构造波及广义导波型构造波来解释。最后，研讨了地球内部波动现象在地震研究中的应用，包括它们在地震危险性分析与地震区划、地震预报以及地震成因研究中的应用。     

COMPUTATION OF ZERO-OFFSET VERTICAL SEISMIC PROFILES INCLUDING GEOMETRICAL SPREADING AND ABSORPTION*

Synthetic vertical seismic profiles (VSP) provide a useful tool in the interpretation of VSP data, allowing the interpreter to analyze the propagation of seismic waves in the different layers. A zero-offset VSP modeling program can also be used as part of an inversion program for estimating the parameters in a layered model of the subsurface. Proposed methods for computing synthetic VSP are mostly based on plane waves in a horizontally layered elastic or anelastic medium. In order to compare these synthetic VSP with real data a common method is to scale the data with the spherical spreading factor of the primary reflections. This will in most cases lead to artificial enhancement of multiple reflections. We apply the ray series method to the equations of motion for a linear viscoelastic medium after having done a Fourier transformation with respect to the time variable. This results in a complex eikonal equation which, in general, appears to be difficult to solve. For vertically traveling waves in a horizontally layered viscoelastic medium the solution is easily found to be the integral along the ray of the inverse of the complex propagation velocity. The spherical spreading due to a point source is also complex, and it is equal to the integral along the ray of the complex propagation velocity. Synthetic data examples illustrate the differences between spherical, cylindrical, and plane waves in elastic and viscoelastic layered media.     

黏弹性介质VSP记录模拟及在估算Q值研究中应用

采用标准线性固体模型,本文建立了黏弹性介质完全匹配层吸收边界的高阶速度-应力交错网格有限差分算法,并对黏弹性介质中的地震波传播进行了数值模拟.基于黏弹性波动方程正演模拟提供的零偏VSP全波场数据,本文进行了质心频移法计算Q值的反演分析.结果表明,反射波、转换波及短程多次波对频谱的影响较大,对Q值反演造成一定误差.本文的...     

Effect of point source and heterogeneity on the propagation of SH-Waves in a viscoelastic layer over a viscoelastic half space

The present paper is concerned with the propagation of shear waves in a homogeneous viscoelastic isotropic layer lying over a semi-infinite heterogeneous viscoelastic isotropic half-space due to point source. The inhomogeneity parameters associated to rigidity, internal friction and density are assumed to be functions of depth. The dispersion equation of shear waves has been obtained using Green’s function technique. The dimensionless angular frequency has been plotted against dimensionless wave number for different values of inhomogeneity parameters. The effects of inhomogeneity have been shown in the dispersion curves. graphical user interface (GUI) software in MATLAB has been developed to show the effect of various inhomogeneity parameters on angular frequency. The topic can be of interest for geophysical applications in propagation of shear waves on the Earth’s crust.     

添加正则化项的黏声逆时偏移成像方法研究

在实际地球介质中传播的地震波会产生衰减和频散现象,因此其更接近于黏弹性介质,在地震处理中补偿这些黏性影响是十分必要的。基于波动方程的叠前深度偏移中进行吸收衰减补偿更准确,也更有物理意义,直接求解双程波动方程的逆时偏移(RTM)能够成像大倾角复杂构造,具有诸多优势。然而当考虑吸收衰减补偿时通常会产生不稳定现象,大部分研究都是在逆时偏移的波场延拓中进行波数域的低通滤波来解决这个问题。本文采用广义标准线性固体的黏声波动方程进行吸收衰减补偿的Q--RTM方法,通过添加正则化项的方式来稳定延拓过程。添加正则化项本质上是低通滤波,滤波窗口是指数形式,在时空域有明确的形式,可以阻止发生高频不稳定。与直接滤波相比,正则化参数可以是空变的,因此比较适合剧烈变化的区域,我们还发现震源归一化互相关成像条件更适合Q--RTM方法。      

Dynamic analysis of large 3-D underground structures by the bem

An up to date literature survey on the dynamics of underground structures is presented briefly. The dynamic response of large three-dimensional underground structures to external or internal dynamic forces or to seismic waves is numerically determined by the frequency domain boundary element method. This method is used to model both the structure and the soil medium, which are assumed to behave as linear elastic or viscoelastic bodies. The full-space dynamic fundamental solution is employed in the formulation and this requires a free soil surface discretization, confined to a finite portion around the area of interest, in addition to soil—structure interface and free structural surface discretizations. The dynamic disturbances can have a harmonic or a transient time variation. The transient case is treated with the aid of numerical Laplace transforms with respect to time. Various numerical examples involving lined cavities and long lined tunnels buried in the full- or the half-space subjected to harmonic or transient external forces or seismic waves are presented to illustrate the method and demonstrate its advantages.