深层地震勘探的地震波传传播理论研究前景

深层地震勘探为地震波传播理论研究提出了新的挑战和机遇。深层地震勘探的主要难点是上覆层的影响甚大，使后续的处理有隔靴挠痒之感，必须应用波场延拓消除上覆层影响。深层波速的高速性和横向不均匀性决定了大角散射和弹性波处理方法的重要性。本文具体评述了深层地震勘探的主要方法对策，深入探讨了波场延拓的李群方法和弹性反演的某些问题，目的在于为深化深层地震提供新的研究手段和方法。     

深层地震勘探的地震波传播理论研究前景

深层地震勘探为地震波传播理论研究提出了新的挑战和机遇.深层地震勘探的主要难点是上覆层的影响甚大,使后续的处理有隔靴挠痒之感,必须应用波场延拓消除上覆层影响.深层波速的高速性和横向不均匀性决定了大角散射和弹性波处理方法的重要性.本文具体评述了深层地震勘探的主要方法对策,深入探讨了波场延拓的李群方法和弹性反演的某些问题,目的在于为深化深层地震勘探提供新的研究手段和方法.     

Three-Dimensional Seismic Wave Propagation by Modal Summation: Method and Validation

It is an acquired result that, in order to enable realistic earthquake hazard assessment and reliable estimation of the ground motion response to an earthquake, three-dimensional velocity models have to be considered. In this paper we present a new analytical procedure for determining the seismic wavefield in a 3D anelastic model based on the combination of the ray theory with the modal summation method. The proposed procedure has been validated by considering the three-dimensional model of the Kanto basin (Japan) available in the literature. Three-dimensional simulations were performed for the 1990 Odawara earthquake. The results obtained were compared both with recorded signals and with simulations available in the literature for several stations located within the Kanto basin. Besides the advantage of being a useful tool for assessment of seismic hazard and seismic risk reduction, it is characterized by high efficiency, in fact, once the study region is identified and the 3D model is constructed, the computation, at each station, of the three components of the synthetic signal (displacement, velocity, and acceleration) takes less than 3?h on a 2?GHz CPU.     

A Hybrid BE-GS Method for Modeling Regional Wave Propagation

—?We present a hybrid boundary-element (BE) and generalized screen propagator (GSP) method for the 2-D SH problem to model the combined effects of arbitrarily irregular topography, large-scale crustal variation, and the associated small-scale heterogeneities on regional wave propagation. We develop a boundary connection technique to couple the wave fields calculated by the BE method with those of the GSP method. Its validity is tested by numerical experiments. For a long crustal waveguide, the relatively short sections with severe surface topography can be modeled by the time-consuming BE method to high frequencies, and the exterior field in the relatively weak heterogeneous media of large volume can be calculated by the GSP method. For the waveguide with severe topography, the BE method can be used section by section via the boundary connection technique to model the combined effects of rough topography and large-scale structural variation on Lg wave propagation at extended regional distances.¶Numerical comparisons with independent methods showed that the hybrid method is relatively accurate for Lg simulation. We apply the hybrid method to Lg wave propagation in two real crustal waveguides in the Tibet region; one with Lg blockage and another without blockage. We found that the most characteristic effect from the irregular topography is the strong scattering by the topographic structures. The scattering by local irregular topographies leads to anomalous near-receive effects and tends to remove energy from the guided waves, which causes decay of amplitude and waveform distortion. It can be expected that rough surface topography and random heterogeneities with scale length close to the dominant wavelength will be very efficient in attenuating regional waves. The dramatic lateral variation of the topography-Moho large-scale structure combined with the small-scale rough topography and random heterogeneities could be the cause of Lg anomalous attenuation and blockage observed in this region. More quantitative assessment of the topographic effects must be conducted in the future.     

应力诱导各向异性介质中地震波的传播

主要讨论了应力变化如何影响各向异性介质中波速度的问题。推导了一般各向异性介质在初始应力下的Christoffel方程,得到介质中3种波的相速度和初始应力的关系表达式;通过实验数据验证了单轴应力能够诱导各向异性,当施加单轴应力时,速度在沿应力的方向增加最大,在垂直应力的方向增加最小,实验结果与理论推导一致;用Christoffel方程的数值解模拟在3种对称情况下的弹性各向异性介质中初始应力对波速度的影响。数值结果表明:初始应力对各向异性介质中波传播速度的影响,随着各向异性强度的增加而增大,而且速度越慢,影响越大。     

粘弹性介质地震波传播的褶积微分算子法数值模拟研究

早期的褶积微分算子法都是基于正反傅立叶变换而实现的,其精度比四阶有限差分稍高。本文将计算数学中的Forsyte广义正交多项式微分算子与褶积算子相结合,构建了一个新的快速、高精度褶积微分算子,其计算结果非常接近实验函数微分的精确值,精度与l6阶有限差分相当。粘弹性波动方程更真实地描述了实际地下介质中弹性波的传播规律及其波场特征。本文以二维粘弹性波动方程为例,推导了粘弹性介质波动方程的离散格式,用迭积微分算子法实现了粘弹性介质的地震波场正演模拟,并对其波传播特征进行了分析。计算结果表明该算法能正确模拟粘弹性介质中的地震波,正确地反映粘弹性介质中波场的传播规律。     

Numerical Simulation of the Effect of a DC Electric Field on Seismic Wave Propagation with the Pseudospectral Time Domain Method

We have modeled the effect of a direct current (DC) electric field on the propagation of seismic waves by the pseudospectral time domain (PSTD) method, based on a set of governing equations for the poroelastic media. This study belongs to the more general term of the seismoelectric coupling effect. The set of physical equations consists of the poroelastodynamic equations for the seismic waves and the Maxwell's equations for the electromagnetic waves; the magnitude of the seismoelectric coupling effect is characterized by the charge density, the electric conductivity, the Onsager coefficient, a function of the dielectric permittivity, the fluid viscosity, and the zeta potential. The poroelastodynamic vibration of a solid matrix generates an electric oscillation with the form of streaming current via the fluctuation of pore pressure. Meanwhile, fluctuating pore pressure also causes oscillatory variation of the electric resistivity of the solid matrix. The simulated poroelastic wave propagation and electric field variation with an existing background DC electric field are compared with the results of a physical experiment carried out in an oilfield. The results show that the DC electric field can significantly affect the propagating elastic energy through the seismoelectric coupling in a wide range of the seismic frequency band.     

Coupled Simulation of Seismic Wave Propagation and Failure Phenomena by Use of an MPS Method

The failure of brittle materials, for example glasses and rock masses, is commonly observed to be discontinuous. It is, however, difficult to simulate these phenomena by use of conventional numerical simulation methods, for example the finite difference method or the finite element method, because of the presence of computational grids or elements artificially introduced before the simulation. It is, therefore, important for research on such discontinuous failures in science and engineering to analyze the phenomena seamlessly. This study deals with the coupled simulation of elastic wave propagation and failure phenomena by use of a moving particle semi-implicit (MPS) method. It is simple to model the objects of analysis because no grid or lattice structure is necessary. In addition, lack of a grid or lattice structure makes it simple to simulate large deformations and failure phenomena at the same time. We first compare analytical and MPS solutions by use of Lamb’s problem with different offset distances, material properties, and source frequencies. Our results show that analytical and numerical seismograms are in good agreement with each other for 20 particles in a minimum wavelength. Finally, we focus our attention on the Hopkinson effect as an example of failure induced by elastic wave propagation. In the application of the MPS, the algorithm is basically the same as in the previous calculation except for the introduction of a failure criterion. The failure criterion applied in this study is that particle connectivity must be disconnected when the distance between the particles exceeds a failure threshold. We applied the developed algorithm to a suspended specimen that was modeled as a long bar consisting of thousands of particles. A compressional wave in the bar is generated by an abrupt pressure change on one edge. The compressional wave propagates along the interior of the specimen and is visualized clearly. At the other end of the bar, the spalling of the bar is reproduced numerically, and a broken piece of the bar is formed and falls away from the main body of the bar. Consequently, these results show that the MPS method effectively reproduces wave propagation and failure phenomena at the same time.     

Arbitrary Difference Precise Integration Method for Solving the Seismic Wave Equation

Wave equation migration is often applied to solve seismic imaging problems. Usually, the finite difference method is used to obtain the numerical solution of the wave equation. In this paper, the arbitrary difference precise integration (ADPI) method is discussed and applied in seismic migration. The ADPI method has its own distinctive idea. When dispersing coordinates in the space domain, it employs a relatively unrestrained form instead of the one used by the conventional finite difference method. Moreover, in the time domain it adopts the sub-domain precise integration method. As a result, it not only takes the merits of high precision and narrow bandwidth, but also can process various boundary conditions and describe the feature of an inhomogeneous medium better. Numerical results show the benefit of the presented algorithm using the ADPI method.     

基于弹性波CT技术的岩体破裂探测方法

弹性波层析成像技术简称“弹性波CT扫描”,是在不损坏物体的前提下,利用弹性波射线穿透地层时,其走时及振幅与地层内部的某些物理参数存在线性积分关系的这一关键特征,反演地层内部三维速度结构或衰减特性的方法。本文基于弹性波CT技术,通过孔间岩体慢度反演,综合钻孔编录及工程现场情况,对承德市半壁山危岩体中破裂发育情况进行综合解译,测定岩体破裂发育的位置和规模。实践证明,采用弹性波CT方法探测得到的破裂位置与钻孔揭露的情况吻合,为危岩体的整治提供了依据。     

VTI介质准P波旋转交错有限差分数值模拟

本文采用旋转交错网格差分格式对VTI(垂直对称轴的横向各向同性)介质准P波一阶应力-速度方程进行数值模拟。并在PML边界条件和稳定性条件下得出Marmousi等复杂模型的高精度波场快照和地震记录,分析了各向异性对地震波的影响。数值结果表明:旋转交错网格有限差分能获得高精度的地震模拟数据,PML边界有较好的吸收效果。     

Characteristics of Seismic Wave Propagation in the Binchuan Region of Yunnan Using a Dense Seismic Array and Large Volume Airgun Shots

The Binchuan region of Yunnan is a structurally complex region with mountains, basins, and active faults. In this situation,seismic wave propagation exhibits complex characteristics due to strong heterogeneity of underground media instead of following the great-circle path. In order to obtain a high-resolution shallow crustal structure, a dense seismic array was deployed during March 21 to May 30, 2017 in this area. To better understand the complexities of seismic wave propagation in this region, we perform array-based frequency-domain beamforming analysis and single-station based polarization analysis to investigate the characteristics of seismic wave propagation, using airgun-generated P-wave signals recorded by dense array stations in this experiment. The results from these two methods both reveal similar but complex characteristics of seismic wave propagation in the Binchuan basin. The azimuth anomalies off the great-circle path are quite large with values up to 30°, which is caused by strong structural heterogeneity in the very shallow crust. Our research provide a better understanding of the complex geologic structures in this area and provide guidance for detecting concealed faults and distribution of velocity anomalies.     

地震波在盆地中的传播特点及其对盆地中震害的影响

通过数值模拟表明,对于具有一定尺度并填充了低速沉积物的盆地,地震发生时入射的体波会激发出在盆地内往返传播的短周期面波,从而造成盆地内大振幅长持续时间的振动,这大大增加了地震对盆地中结构物的破坏作用。针对盆地是当地经济、文化发展的中心,又常常面临一定的地震危险性的问题,提出了进一步开展盆地结构对地震响应的研究工作的几点建议。     

求解波动方程的任意差分精细积分法

在地震偏移成像技术中，常常要反向外推波场，因此涉及到波动方程的数值求解问题。本文提出了一种求解偏微分方程的新的半解析方法——任意差分精细积分(ADPI)法。其大体思路是：空间域上作坐标离散，但不采用古典差分法的等分离散方式，而是一种相对自由的、任意的离散法；时间域上则采用子域精细积分的方法，既保留了精细积分法的高精度，又克服了工作量大、占用存储大等缺点。该方法具有精度高、带宽小、稳定性好等多项突出优点，并且可以灵括处理各类边界条件。本文从简单一维、较普遍一维、以及二维3种情形讨论该方法对波动方程的具体应用，结合实际的算例，详细分析了各种算法的可行性和精度特点。     

The One-Way Wave Equation: A Full-Waveform Tool for Modeling Seismic Body Wave Phenomena

The study of seismic body waves is an integral aspect in global, exploration and engineering scale seismology, where the forward modeling of waves is an essential component in seismic interpretation. Forward modeling represents the kernel of both migration and inversion algorithms as the Green’s function for wavefield propagation and is also an important diagnostic tool that provides insight into the physics of wave propagation and a means of testing hypotheses inferred from observational data. This paper introduces the one-way wave equation method for modeling seismic wave phenomena and specifically focuses on the so-called operator-root one-way wave equations. To provide some motivation for this approach, this review first summarizes the various approaches in deriving one-way approximations and subsequently discusses several alternative matrix narrow-angle and wide-angle formulations. To demonstrate the key strengths of the one-way approach, results from waveform simulation for global scale shear-wave splitting modeling, reservoir-scale frequency-dependent shear-wave splitting modeling and acoustic waveform modeling in random heterogeneous media are shown. These results highlight the main feature of the one-way wave equation approach in terms of its ability to model gradual vector (for the elastic case) and scalar (for the acoustic case) waveform evolution along the underlying wavefront. Although not strictly an exact solution, the one-way wave equation shows significant advantages (e.g., computational efficiency) for a range of transmitted wave three-dimensional global, exploration and engineering scale applications.     

Seismoelectric Effect Associated with Rayleigh Wave Propagation

Izvestiya, Physics of the Solid Earth - Abstract—In the scope of Frenkel’s equation, an analytical solution is obtained for pore pressure and electrokinetically induced electric field...     

各向异性双相介质弹性波场褶积算法数值模拟

从各向同性介质中波场数值模拟的褶积微分算子法出发,推导出了各向异性双相介质中波场传播数值计算的褶积新算法.将常见的二阶微分Biot波动方程用等效的一阶速度—应力双曲方程表示,其中未知的波场向量包括固相和流体的速度分量和应力分量,由此对方程的时间项使用交错网格差分方法计算,而对空间项则采用褶积微分算法进行求解.对各向异性双相介质在单层介质模型和双层介质模型中的波场特征进行了研究.研究的结果显示,在两层介质分界面上当地震波产生反射时能观测到两类纵波和横波,并且在衰减系数大的介质里慢纵波很难见到.     

Improvement in the Fault Boundary Conditions for a Staggered Grid Finite-difference Method

The staggered grid finite-difference method is a powerful tool in seismology and is commonly used to study earthquake source dynamics. In the staggered grid finite-difference method stress and particle velocity components are calculated at different grid points, and a faulting problem is a mixed boundary problem, therefore different implementations of fault boundary conditions have been proposed. Viriuex and Madariaga (1982) chose the shear stress grid as the fault surface, however, this method has several problems: (1) Fault slip leakage outside the fault, and (2) the stress bump beyond the crack tip caused by S waves is not well resolved. Madariaga et al. (1998) solved the latter problem via thick fault implementation, but the former problem remains and causes a new issue; displacement discontinuity across the slip is not well modeled because of the artificial thickness of the fault. In the present study we improve the implementation of the fault boundary conditions in the staggered grid finite-difference method by using a fictitious surface to satisfy the fault boundary conditions. In our implementation, velocity (or displacement) grids are set on the fault plane, stress grids are shifted half grid spacing from the fault and stress on the fictitious surface in the rupture zone is given such that the interpolated stress on the fault is equal to the frictional stress. Within the area which does not rupture, stress on the fictitious surface is given a condition of no discontinuity of the velocity (or displacement). Fault normal displacement (or velocity) is given such that the normal stress on the fault is continuous across the fault. Artificial viscous damping is introduced on the fault to avoid vibration caused by onset of the slip. Our implementation has five advantages over previous versions: (1) No leakage of the slip prior to rupture and (2) a zero thickness fault, (3) stress on the fault is reliably calculated, (4) our implementation is suitable for the study of fault constitutive laws, as slip is defined as the difference between displacement on the plane of z = + 0 and that of z = − 0, and (5) cessation of slip is achieved correctly.     

基于紧凑存储的任意四边形网格有限元法地震波场数值模拟

采用有限元法精确模拟复杂介质条件下的地震波场,一般采用三角单元,但在节点数相同的情况下,三角单元的计算精度不如矩形单元高,采用三角单元模拟复杂界面时,编制确定结构刚度矩阵非零元素位置的程序也较为麻烦。采用矩形单元离散含有倾斜或起伏界面的地质模型时,无法避免绕射噪声,若加密网格又会增加计算量。为此,本文基于任意四边形单元模拟声波的传播,在倾斜或起伏界面条件下,可以有效避免因离散引起的“阶梯状”界面,在不增加计算量以及内存占用的前提下,有效地消除离散绕射噪声。采用对角的集中质量矩阵代替一致质量矩阵,避免矩阵的求逆运算,从而提高显式有限元法的计算效率;对结构刚度矩阵采用紧凑存储格式,每一行需要存储的元素最多为5个,同时零元素不参与运算,既减少内存的占用,又极大地提高计算效率。