细胞自动机在地震波传播研究中的应用

本文基于细胞自动机在地震波传播研究中的最近成果,阐述了其基本的研究思路与理论框架,给出了一个计算实例．在此基础上就细胞自动机方法与传统波动方程的衔接关系及复杂介质中地震波正反问题作了讨论,并对研究前景进行展望．     

细胞自动机在地震波传播研究中的应用

本文基于细胞自动机在地震波传播研究中的最近成果,阐述了其基本的研究思路与理论框架,给出了一个计算实例．在此基础上就细胞自动机方法与传统波动方程的衔接关系及复杂介质中地震波正反问题作了讨论,并对研究前景进行展望．     

地震波散射研究的若干重要进展

本文从地球介质的复杂性与非均匀性的普遍性以及地震波在其中的传播过程的复杂性出发,对地震波散射理论及方法研究的历史进行了简要的回顾,并对该领域从20世纪90年代以来的某些进展作了简要的介绍与评述.本文分两大部分进行阐述.(1)．历史回顾：简介并回顾了地震波散射理论几十年的发展历程、存在的问题及对解决这些问题的潜在的基本途径.(2)．20世纪90年代以来的若干进展：简要介绍了弱散射理论体系的形成及强散射问题研究的部分成果,提出了散射理论未来发展的可能方向之一,即在无近似的拟微局部分析理论的基础上,建立并发展可处理高度复杂的地球固体介质中地震波传播问题的地震波散射及全波理论.     

减轻地震灾害://c

回顾了过去4年来中国在减轻地震灾害方面的研究进展．地震灾害定量化的研究结果表明,随着社会经济的发展和人口城市化的加快,地震造成的灾害将越来越严重．减轻地震灾害的研究,出现了一些新的趋势:从研究地震危险性向研究地震危害性的过渡;从研究工程灾害向研究社会灾害的过渡;以及发展了以社区为中心的减灾体系．      

横向非均匀介质中弹性地震波传播的数值模拟

应用混合变量弹性动力学方程和线性常微分方程组的矩阵指数解法,将层状介质中广泛应用的弹性波传播矩阵解法推广至横向非均匀介质,给出了一种可计算复杂地质体中弹性波传播的广义传播矩阵数值解法。该方法可模拟任意震源及所产生的各种体波、面波,数值结果表明具有很高的计算精度。     

地震波散射:理论与应用

传统的球面对称（或层状构造）地球模型正经历着一场革命。地球被揭示从地壳、地幔到地核到处都呈现多尺度的横向非均匀性。这些具有不同尺度的非均匀体对地震波具有不同的效应。速度和密度的非均匀体能改变波形,引起走时和振幅的起伏以及产生直达波的视衰减。地球岩石层的非均匀体还能产生P尾波、S尾波和Lg尾波等。核-幔边界附近的非均匀体能产生对PKP波的散射而成为PKIKP的前驱波,PKKP波的散射波可成为主震相自己的前驱波。近源和近台站的复杂构造可通过共振、散射来改变地震波形。粗糙地形或粗糙界面能造成体波和面波的耦合。地壳内规则排列的裂隙可产生有效各向异性而使S波分裂。由三维非均匀体所引起的地震波的变化,在广义上被称为地震波散射。近十多年来,由于高质量的高频数字地震资料的逐渐增多,对地震波散射的研究在急速发展并引起了越来越多的地震学家、工程学家和勘探地球物理学家的兴趣。本文综述了地震波散射的基本理论和在这一领域各方面的最新进展。其内容大致为:一、地球横向非均匀性的谱及各种散射态式二、地震波散射的研究方法1.理论研究（1）不连续非均匀介质的边界匹配方法（2）弱散射的微扰法（3）高频近似法（4）随机方法和非均匀体的统计特性2.数值模拟和物理模型试验3.野外观测三、弹性波散射的基本特征和标量波近似1.弹性波瑞雷散射2.弹性波瑞雷-甘斯散射3.随机介质的弹性波散射四.地震波散射的表现和应用1.透射起伏2.尾波产生及包络消减3.散射衰减4.核-幔边界附近的散射5.地表地形、近地表结构和深部构造引起的散射6.裂缝散射和有效各向异性7.散射和非线性。     

Studies on seismic waves

The development of seismic wave study in China in the past four years is reviewed. The discussion is divided into several aspects, including seismic wave propagation in laterally homogeneous media, laterally heterogeneous me-dia, anisotropie and porous media, surface wave and seismic wave inversion, and seismic wave study in prospect-ing and logging problems. Important projects in the current studies on seismic wave is suggested as the develop-ment of high efficient numerical methods, and applying them to the studies of excitation and propagation of seis-mic waves in complex media and strong ground motion, which will form a foundation for refined earthquake haz-ard analysis and prediction.     

双相介质中地震波衰减的物理机制

High-frequency seismic attenuation is conventionally attributed to anelastic absorption. In this paper, I present three studies on high-frequency seismic attenuation and propose that the physical mechanism results from the interference of elastic microscopic multiple scattering waves. First, I propose a new theory on wave propagation in a two-phase medium which is based on the concept that the basic unit for wave propagation is a nano- mass point. As a result of the elasticity variations of pore fluid and rock framework, micro multiple scattering waves would emerge at the wavelength of the seismic waves passing through the two-phase medium and their interference and overlap would generate high- frequency seismic attenuation. Second, I present a study of the frequency response of seismic transmitted waves by modeling thin-layers with thicknesses no larger than pore diameters. Results indicate that high-frequency seismic waves attenuate slightly in a near-surface water zone but decay significantly in a near-surface gas zone. Third, I analyze the seismic attenuation characteristics in near-surface water and gas zones using dual-well shots in the Songliao Basin, and demonstrate that the high-frequency seismic waves attenuate slightly in water zones but in gas zones the 160-1600 Hz propagating waves decay significantly. The seismic attenuation characteristics from field observations coincide with the modeling results. Conclusions drawn from these studies theoretically support seismic attenuation recovery.     

时间域地震全波形反演方法进展

地震全波形反演(Full Waveform Inversion)利用地震波场的运动学和动力学信息建立地层速度模型,能够精确刻画模型细节,成为近年来的研究热点.本文对日渐成熟的时间域全波形反演方法的研究进行了综述,着重评述了地震波场模拟方法、震源子波的处理方式、目标泛函的建立方式、优化反演方法、梯度预处理方式等关键环节的进展,指出了全波形反演方法向分频分尺度、全局搜索与局部搜索联合的优化反演、时间域正演和频率域反演的混合域反演等多种技术有机联合的方向发展.     

Seismic wave scattering inversion for fluid factor of heterogeneous media

Elastic wave inverse scattering theory plays an important role in parameters estimation of heterogeneous media. Combining inverse scattering theory, perturbation theory and stationary phase approximation, we derive the P-wave seismic scattering coefficient equation in terms of fluid factor, shear modulus and density of background homogeneous media and perturbation media. With this equation as forward solver, a pre-stack seismic Bayesian inversion method is proposed to estimate the fluid factor of heterogeneous media. In this method, Cauchy distribution is utilized to the ratios of fluid factors, shear moduli and densities of perturbation media and background homogeneous media, respectively. Gaussian distribution is utilized to the likelihood function. The introduction of constraints from initial smooth models enhances the stability of the estimation of model parameters. Model test and real data example demonstrate that the proposed method is able to estimate the fluid factor of heterogeneous media from pre-stack seismic data directly and reasonably.     

Elastic waves in nonhomogeneous media under 2D conditions: II. Numerical implementation

The purpose of this work is to present three methods of analysis for elastic waves propagating in two dimensional, elastic nonhomogeneous media. The first step, common to all methods, is a transformation of the governing equations of motion so that derivatives with respect to the material parameters no longer appear in the differential operator. This procedure, however, restricts analysis to a very specific class of nonhomogeneous media, namely those for which Poisson's ratio is equal to 0.25 and the elastic parameters are quadratic functions of position. Subsequently, fundamental solutions are evaluated by: (i) conformal mapping in conjunction with wave decomposition, which in principle allows for both vertical and lateral heterogeneities; (ii) wave decomposition into pseudo-dilatational and pseudo-rotational components, which results in an Euler-type equation for the transformed solution if medium heterogeneity is a function of one coordinate only; and (iii) Fourier transformation followed by a first order differential equation system solution, where the final step involving inverse transformation from the wavenumber domain is accomplished numerically. Finally, in the companion paper numerical examples serve to illustrate the above methodologies and to delineate their range of applicability.     

Upper mantle P wave velocity structure of the northern part of China and Mongolia

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Three dimensional shear wave velocity structure of crust and upper mantle in South China Sea and its adjacent regions by surface waveform inversion

IntroductionHistorically, surface waves provided much of our understanding of the lateral heterogeneity in the crust and the upper mantle, especially in oceans or desert areas. Traditional method utilizes the great circle theorem for surface waves. It assumed that surface wave propagates along the great circle connecting epicenter with station. Firstly, traditional surface wave analysis was carried out by using multi-frequency-filter dispersion analysis to acquire the group or phase velocity d…