基于时频分析方法提取瞬态瑞利波频散曲线

作为一种无损浅层勘探方法,瑞利波越来越多地应用于地震工程、环境工程及岩土工程测试中。其中,一项重要的工作是提取瑞利波的频散曲线。根据激振方式不同,瑞利波勘探可分为稳态法、瞬态法和地脉动台阵法。基于相位谱法提取瞬态瑞利波的频散曲线,一般将两通道瑞利波的相位差限制在2π之内,因此限制了两拾振器之间的布点距离。本文利用时频分析方法,分析了瞬态瑞利波法频散曲线的提取方法,避免了对相位差的限制。数值试验结果表明,采用时频分析方法提取到的频散曲线具有较高的精度。     

煤层厚度变化时地震槽波理论频散曲线计算方法及频散特征分析

槽波地震勘探利用槽波的频散特性反演煤层的结构特征,故理论频散曲线的计算是一个重要方面.使用水平层状模型假设下的面波频散曲线计算方法能够计算煤层厚度恒定模型地震槽波频散曲线;但当煤层厚度变化时该方法不再适用.基于前人水平层状均匀介质模型的面波理论频散曲线计算方法,对于含煤三层模型,本文发展了煤层厚度变化情况下的地震槽波理论频散曲线计算方法,并使用该方法计算分析了不同厚度函数模型的频散曲线形态特征.研究表明：与稳定厚度煤层相比,煤层厚度变化使得地震槽波群速度成为与频率及传播射线在水平面投影路径相关的二元函数;射线路径上煤层厚度的变化使得频散曲线在群速度方向上压缩,群速度变化范围变小,且使处于最小值位置的埃里相群速度增大;而煤层厚度的线性变化模型频散曲线只与射线首、尾处的煤层厚度有关,与煤层厚度恒定模型相比,曲线形态不发生改变;煤层厚度呈非线性变化时,频散曲线形态上可能发生改变.     

利用多重滤波方法提取面波频散曲线

多重滤波方法已被证明在分析面波的频散特性时是一种有效而快速的方法。本文用单个台站的单次地震事件记录,应用MFT(Multiple Filter Technique)方法提取了内华达地区的面波频散曲线并分析了其特征,认为其具有大陆基振型瑞利波频散曲线的典型特征。还利用广义反透射系数法快速计算了瑞利面波频散曲线,尤其是基阶瑞利波相速度及群速度频散曲线;并且在由振型叠加方法合成的理论地震图的基础上,通过比较理论频散曲线和MFT方法得到的频散曲线,研究了多重滤波的可靠性。     

基于瑞利波高阶模式反演的实验研究

通过超声实验研究了沿分层介质，特别是含有低速层的分层介质传播的瑞利波频散特征. 分别对有机玻璃/钢构成的两层速度递增的半空间和铝/有机玻璃/钢构成的含有低速层的三层半空间进行了超声探测实验，采用频率波数分析方法分析了多模式的瑞利波频散曲线，对于速度递增的两层半空间，得到了第一和第二个模式的频散曲线; 对于含有低速层的三层介质，实验得到的频散曲线在不同频段对应不同的模式，从而在模式之间产生跳跃, 分析表明模式跳跃是由各个模式在表面位移幅度的不同分布引起的. 文中明确指出了低速层存在时，反演研究不仅要考虑各模式的频散特性，同时还要考虑不同模式在表面的位移分布情况，给出了低速层存在时的反演方法，避免了模式的误判. 利用遗传算法对两种实验模型的介质参数进行了反演，得到了和实际参数吻合的反演结果.     

多模式瑞雷波频散曲线的粒子群反演方法研究

通常情况下对于瑞雷波频散特性的讨论和分析主要针对其基阶模式.实际上,对于某一给定频率,可能会有多个不同相速度满足频散方程,即存在高阶模式.为了获得更精确的横波速度信息,应适当地在反演过程中加入高阶模式的频散曲线.本文从简单的三层层状介质模型出发,利用频散函数的正演计算得到多模式的频散曲线,并采用改进的粒子群算法分别对基阶模式和多模式频散曲线进行反演.研究结果表明:多模式频散曲线的反演结果相对于基阶模式而言,可靠性和分辨率在一定程度上得到了很大的提高.     

VTI地层井孔模式波理论频散计算时伪极点的影响

波的频散特征在声波测井中有着十分关键的作用.VTI地层下井孔模式波的理论频散曲线可根据频散方程求解.本文首先采用常用的耦合位移势函数对应的频散方程进行了VTI地层斯通利波理论频散曲线的求解.结果发现,在一定各向异性强度范围内,会得到两种计算结果:一条常规斯通利波频散曲线和一条非频散曲线.这是频散矩阵行列式在该模型下存在两个零点导致的.进一步采用一种对称形式的位移势函数推导的对称频散矩阵时分析发现,非频散曲线对应的零点k~2-q~2_p=0为频率—波数响应函数的一个伪极点.经分析,在横波速度范围内,满足伪极点存在的Thomsen参数γ有一定范围,通常在弱各向异性地层中存在.且满足伪极点存在的Thomsen参数γ范围与地层泊松比成负相关,泊松比越小,满足伪极点存在的γ范围越大.在计算理论频散曲线时应消除k~2-q■这一公因式的影响,避免得到错误的计算结果,进而影响各向异性反演等计算结果.     

瑞利面波频散曲线贝叶斯反演及其在活断层调查中的应用

瑞利波具有强能量和频散特性,面波勘探采集瑞利面波数据分析反演得到横波速度结构,在浅地表勘探领域得到了广泛的应用,根据面波频散反演速度结构是面波勘探的重要环节之一.面波频散与地下介质的弹性参数是非线性关系,全局优化方法是解决非线性反问题的有效办法,贝叶斯方法是一种基于统计的全局优化方法.贝叶斯公式反映了先验信息和条件概率乘积与后验概率之间的正比关系,利用马尔科夫链蒙特卡洛采样方法可以获得后验分布的采样.与其他方法相比,该方法不是给出一个模型最优解,而是统计出模型参数的平均值和方差,平均值即是反演的模型解,方差能对该反演结果的不确定性做出评价.本文采用贝叶斯方法对模拟和实测瑞利面波数据频散曲线进行反演,结果显示,该方法能获得比较精确的横波速度和厚度参数,验证了本文方法可行.在高丽营地区采集了多个单炮面波数据,对数据进行频散谱处理拾取频散曲线,通过贝叶斯反演方法获得了该测线二维横波速度剖面图,有助于划分和解释该测区地层及断层地质构造.     

瑞利波勘探中“之”形频散曲线的形成机理及反演研究

对瑞利波勘探中“之”字形频散曲线形成的物理机理进行了理论分析,研究了诸波模的传播特性及相互关系．指出在地表下存在具有水平界面的软弱夹层和地层裂缝时,瑞利波频散曲线中的“之”字形结构是低速夹层或地层裂缝中出现多模现象的结果．利用阻尼最小二乘法和遗传算法对瑞利波频散曲线反演介质参数进行了研究和分析,发现最小二乘法不适合瑞利波“之”字形反演问题研究,而用遗传算法得到了较好的结果．     

基于面波频散曲线聚类分析的近地表横波速度反演

获取准确的近地表横波速度对复杂地表条件下弹性波地震数据处理和成像非常重要.在浅层面波工程勘探中通过反演提取的频散曲线可以获得近地表横波速度结构.在多道面波频散曲线分析中,频散关系拾取的精度直接影响速度反演结果的可靠性.本文在多道面波叠加及自动拾取频散曲线基础上,提出了基于面波频散曲线聚类分析的近地表横波速度反演方法.该方法充分考虑了低信噪比条件下面波频散曲线的不确定性,通过在频散曲线拾取中引入曼哈顿距离K-Means聚类算法提高频散曲线拾取的准确性.采用多道多窗口叠加技术提高了面波反演对横向速度变化的适应性,通过聚类算法和多窗口叠加提高反演的可靠性,聚类算法获得较准确的频散曲线更利于后续横波速度反演过程.模拟数据算例对比表明本文提出的方法比常规算法效果更好,精度更高.将提出的方法应用于工程勘探和油气勘探的面波数据反演中,结果也验证了该方法的有效性.     

基于平均速度分析的近地表纵波速度反演

面波频散曲线对于横波速度、纵波速度、层厚等近地表地球物理参数的敏感度相差较大,现阶段通过频散曲线可以获得较为精确的近地表横波速度与厚度信息,但无法直接对纵波速度进行反演.研究表明,泊松比对于波长(W)-探测深度(D)关系较为敏感.基于这一发现,本文根据频散曲线与反演获取的横波速度结构计算平均速度,获取W-D关系曲线.但合成数据测试证明,因近地表浅层对应的W-D曲线变化较小,且浅层纵波速度反演不准确会使误差累积,直接反演W-D曲线无法获取可靠的纵波速度剖面.本文改进了基于平均速度分析的近地表纵波速度反演方法,在目标函数中加入了对浅层信息较为敏感的W/D-D信息,同时对W-D曲线与W/D-D曲线进行联合反演.合成数据测试证明可以获取较为准确地浅层与深层纵波速度.将该方法应用于实际地震数据中,联合反演得到的纵波速度剖面与微测井数据较为吻合,证明本文提出的方法可以不借助其他信息,仅通过面波频散信息,获取更为准确地近地表纵波信息.     

用人工源和天然源面波联合探测浅层速度结构.

本文在简要介绍天然源与人工源瑞雷面波勘探基本原理、数据采集和资料处理方法的基础上,结合3个不同场地的探测实例,阐述了天然源和人工源瑞雷面波方法在浅部速度结构探测中的应用效果.结果表明,根据不同的场地条件和探测目的要求,分别采用天然源、人工源瑞雷面波方法提取瑞雷波频散曲线,再用遗传算法反演得到工程场地浅部地层横波速度结构的技术方法是有效和可行的.该方法对于类似工程的浅部横波速度结构探测具有经济适用、简便快捷的优点.     

台站地震资料的时频域自适应极化分析和滤波

提出一种自适应协方差的时频域极化滤波方法。该方法在广义S变换时频方法的基础上,构造时频域自适应协方差矩阵,通过特征分析计算时频域瞬时极化参数,设计极化滤波器,实现多分量地震极化分析和滤波。其优势在于协方差矩阵的分析时窗的长度由多分量地震数据的瞬时频率确定,可以自适应于有效信号的周期,在每个时频点计算极化参数不需要进行插值处理;结合时间频率信息,解决在时间域或频率域波形或频率重叠的信号具有明显的直观性。模型数据及实际三分量台站地震数据处理结果表明,该极化滤波方法在台站地震资料分析和处理方面具有很好的直观性和较高的分辨率。     

Active-source Rayleigh wave dispersion by the Aki spectral formulation

Rayleigh wave imaging is efficient in estimating the shear- (S) wave velocity in near-surface exploration. The key is to accurately extract the dispersion of Rayleigh wave. We propose a method to calculate the dispersion of the active-source Rayleigh wavefield by using the Aki formulation. The spectrum after the cross correlation of two-channel records in the frequency domain is expressed by the Bessel function. Using the corresponding relation between the zero point of the spectrum real part and the Bessel function root, the phase velocity at the discrete frequency point is obtained and the dispersion curve is extracted. First, the theoretical basis and calculation method used in the active-source Rayleigh wave data are introduced. Then, three sets of theoretical models are calculated by this method and the results are consistent with the theoretical dispersion. Finally, we process a group of real Rayleigh wave data and obtain the phase velocity profiles and compared them with the results obtained by the multichannel surface wave analysis method. The effectiveness and applicability of the Aki method in active-source data processing are verified. Compared with multichannel wave processing, the advantage of the Aki method lies in the use of two-channel data in a single-shot record. When the number of acquisition channels in a shot gathers is insufficient or there is a bad channel, the quality of the extracted dispersion is guaranteed.     

时频域相位滤波在远震接收函数噪声压制中的应用

宽频带地震观测数据中有效信号和干扰噪声经常发生混频效应,常规的频率域滤波方法很难将二者分离.地震波信号属于时变非平稳信号,时频分析方法能够同时得到地震波信号随着时间和频率变化的振幅和相位特征,S变换是其中较为高效的时频分析工具之一.本文以S变换为例,提出了基于相位叠加的时频域相位滤波方法.与传统叠加方法相比,相位叠加方法对强振幅不敏感,对波形一致性相当敏感,更加利于有效弱信号信息的检测.时频域相位滤波方法滤除与有效信号不相干的背景噪声,保留了相位一致的有效信号成分,显著提高了信噪比.运用理论合成的远震接收函数数据和实际的宽频带地震观测数据检验结果显示该方法较传统的带通滤波方法相比,即使在信噪较低且混频严重条件下,时频域相位滤波方法的滤波效果依然很明显,有助于识别能量较弱的有效信号.     

四种典型地层的瑞雷波“之”字型频散曲线数值模拟研究

虽然MASW技术已经广泛地应用于地基检测中,但由于缺少大量理论指导,特别是数值模拟方面的研究,其应用受到限制.本文基于有限元软件LS-DYNA,通过数值模拟研究了四种典型地层（递增型地层、含软弱下伏层地层、含软弱夹层地层和硬夹层地层）由MASW方法提取的瑞雷波频散曲线的“之”字型特征.发现对于递增型地层,频散曲线不会出现“之”字型,对于其他三种地层,频散曲线则会出现不同类型的“之”字型,其中含软弱夹层地层“之”字型的位置和尺寸与软夹层的位置和层厚有较好的对应关系.本文的研究结果为实际工程中利用瑞雷波频散曲线的形状判定地层类型和软弱夹层位置提供了重要参考.     

Dispersion calculation method based on S-transform and coordinate rotation for Love channel waves with two components

Dispersion analysis is an important part of in-seam seismic data processing, and the calculation accuracy of the dispersion curve directly influences pickup errors of channel wave travel time. To extract an accurate channel wave dispersion curve from in-seam seismic two-component signals, we proposed a time–frequency analysis method based on single-trace signal processing; in addition, we formulated a dispersion calculation equation, based on S-transform, with a freely adjusted filter window width. To unify the azimuth of seismic wave propagation received by a two-component geophone, the original in-seam seismic data undergoes coordinate rotation. The rotation angle can be calculated based on P-wave characteristics, with high energy in the wave propagation direction and weak energy in the vertical direction. With this angle acquisition, a two-component signal can be converted to horizontal and vertical directions. Because Love channel waves have a particle vibration track perpendicular to the wave propagation direction, the signal in the horizontal and vertical directions is mainly Love channel waves. More accurate dispersion characters of Love channel waves can be extracted after the coordinate rotation of two-component signals.     

黏弹性介质瑞雷波有限差分模拟与特性分析

本文通过数值模拟研究了介质黏弹性对瑞雷波传播的影响.模拟采用结合了交错Adams-Bashforth时间积分法、应力镜像法和多轴完美匹配层的标准交错网格高阶有限差分方案.通过模拟结果和理论结果对比,测试了方法的精度,验证了结果的正确性.在均匀半空间模型中,分别从波场快照、波形曲线及频散能量图三个角度,对黏弹性介质瑞雷波衰减和频散特性进行了详细分析.两层速度递增模型被用于进一步分析瑞雷波在黏弹性层状介质中的特性.结果表明：由于介质的黏弹性,瑞雷波振幅发生衰减,高频成分比低频成分衰减更剧烈,衰减程度随偏移距增大而增强;瑞雷波相速度发生频散,且随频率增大而增大,频散能量的分辨率有所降低;黏弹性波动方程中的参考频率,不会影响瑞雷波振幅衰减和相速度频散的程度,但决定了黏弹性和弹性介质瑞雷波相速度相等的频率位置.本研究有助于人们更好地理解地球介质中瑞雷波的行为,并为瑞雷波勘探的应用和研究提供了科学和有价值的参考.     

Rayleigh wave separation using high-resolution time-frequency polarization filter

Obtaining geological information from seismic data motivates researchers to innovate and improve seismic wave processing tools. Polarization-based methods have received much attention regarding their ability to discriminate between different phases of the seismic wave based on polarity. Combining the intuitive definition of polarity in the frequency domain (monochromatic waves) with the non-stationary properties provided by time-domain methods, time-frequency approaches are attracting widespread interest because they localize the information extracted from the seismic waves in the joint time and frequency domains. Due to the lack of high-resolution time-frequency maps, the time-frequency polarization approach was not able to resolve specific temporal polarity changes in the seismic signal. The main objective of this study was to devise a robust time-frequency-based polarization filtering method using high-resolution polarization attributes obtained directly from the sparse time-frequency map without using Eigen analysis or analytic signals. The method proposed here utilizes a computationally effective sparsity-based adaptive S-transform to obtain a high-resolution polarization map of an inherently non-stationary seismogram for the entire frequency content of the signal at different times. The superiority of the proposed method over the S-transform method was verified using synthetic and real data sets to calculate the polarization attributes in the time-frequency domain and separate the Rayleigh waves from the seismogram.     

Dispersion features of transmitted channel waves and inversion of coal seam thickness

In-seam seismic survey currently is a hot geophysical exploration technology used for the prediction of coal seam thickness in China. Many studies have investigated the relationship between the group velocity of channel wave at certain frequency and the actual thickness of exposed coal beds. But these results are based on statistics and not universally applicable to predict the thickness of coal seams. In this study, we first theoretically analyzed the relationship between the depth and energy distribution of multi-order Love-type channel waves and found that when the channel wave wavelength is smaller than the thickness of the coal seam, the energy is more concentrated, while when the wavelength is greater than the thickness, the energy reduces linearly. We then utilized the numerical simulation technology to obtain the signal of the simulated Love-type channel wave, analyzed its frequency dispersion, and calculated the theoretical dispersion curves. The results showed that the dispersion characteristics of the channel wave are closely related to the thickness of coal seam, and the shear wave velocity of the coal seam and its surrounding rocks. In addition, we for the first time realized the joint inversion of multi-order Love-type channel waves based on the genetic algorithm and inversely calculated the velocities of shear wave in both coal seam and its surrounding rocks and the thickness of the coal seam. In addition, we found the group velocity dispersion curve of the single-channel transmitted channel wave using the time–frequency analysis and obtained the phase velocity dispersion curve based on the mathematical relationship between the group and phase velocities. Moreover, we employed the phase velocity dispersion curve to complete the inversion of the above method and obtain the predicted coal seam thickness. By comparing the geological sketch of the coal mining face, we found that the predicted coal seam thickness is in good agreement with the actual thickness. Overall, adopting the channel wave inversion method that creatively uses the complete dispersion curve can obtain the shear wave velocities of the coal and its surrounding rocks, and analyzing the depth of the abruptly changed shear wave velocity can accurately obtain the thickness of the coal seam. Therefore, our study proved that this inversion method is feasible to be used in both simulation experiments and actual detection.