HTI煤层介质槽波波场与频散特征初步研究

煤层内裂隙较为发育,具有明显的各向异性.目前槽波理论研究以各向同性介质为主,对HTI介质中槽波及其频散性质研究很少.本文以弱各向异性、含垂直裂隙HTI煤层介质为研究对象,研究了HTI煤层介质中的三维槽波波场,采用交错网格高阶有限差分法模拟槽波,推导了三层水平层状HTI煤层介质的Love型槽波理论频散公式和振幅深度分布,分析了HTI各弹性参数对频散曲线的影响.HTI介质和各向同性介质基阶Love槽波频散曲线差异较小,高阶较大;煤厚主要影响Airy相频率,而Airy相速度不变;煤层vs对Airy相速度影响很大;煤层γ对基阶Love槽波影响很小,高阶稍大.各波偏振方向不再与波的传播方向平行或垂直,而是呈一定夹角.利用基阶Love槽波频散曲线推测裂隙发育较为困难,可利用高阶频散曲线.     

SEISMIC MODELLING WITH CHANNEL WAVES IN SEAM STRUCTURES INFLUENCED BY MYLONITE ZONES1

Channel waves generated in coal-seams and their reflections from discontinuities are widely used to indicate the tectonic and stratigraphic features of coal deposits, resulting in greater efficiency and safety in coal-mining. In the mining area of Ibbenbüren (F.R.G.) seam structures sometimes contain so-called mylonite zones, which are crushed coal deposits capable of binding gas. If mining hits a mylonite zone this would probably not only reduce output of the mine, but could even cause gas explosions. To investigate the influence of a mylonite zone on the propagation of channel waves, Rayleigh channel wave measurements for 2D analogue models were performed and synthetic seismograms of Love channel waves were calculated. Analogue modelling of the mylonite zone using Rayleigh seam waves within the seam was carried out using a perforation technique. Calculations were made to obtain an estimate of velocity reduction due to perforation. The results agree well with velocity values measured up to a perforation of 25% in a 2D epoxy resin model. Reflected channel wave energy was found by applying dispersion analysis in the case where the impedance reduction between the mylonite seam structure and the undisturbed seam was approximately 5%. The horizontal width of the mylonite structure was detectable from the time lag between reflected channel wave signals from both in-seam borders of the mylonite zone. Resolution of two discrete borders was possible for a width of 1.5 λ's. The influence of a vertical fault, positioned within the mylonite zone, could only poorly be resolved. Numerical model investigations of Love seam waves were concerned mainly with the variation of the horizontal width of the mylonite zone. Mylonite zones with dimensions of the order of 0.4 λ's allow definite statements about their widths from dispersion and spectral analyses. For zones with smaller widths down to 0.2 λ's, it was found that reflectivity and transmissivity analyses give a qualitative criterion for distinguishing a mylonite structure surrounding a fault from a pure fault.     

Estimation of rocking and torsion associated with surface waves extracted from recorded motions

By exploiting the capability of identifying and extracting surface waves existing in a seismic signal, we can proceed to estimate the angular displacement (rotation about the horizontal axis normal to the direction of propagation of the wave; rocking) associated with Rayleigh waves as well as the angular displacement (rotation about the vertical axis; torsion) associated with Love waves.For a harmonic Rayleigh (Love) wave, rocking (torsion) would be proportional to the harmonic vertical (transverse horizontal) velocity component and inversely proportional to the phase velocity corresponding to the particular frequency of the harmonic wave (a fact that was originally exploited by Newmark (1969) [15] to estimate torsional excitation). Evidently, a reliable estimate of the phase velocity (as a function of frequency) is necessary. As pointed out by Stockwell (2007) [17], because of its absolutely referenced phase information, the S-Transform can be employed in a cross-spectrum analysis in a local manner. Following this suggestion a very reliable estimate of the phase velocity may be obtained from the recordings at two nearby stations, after the dispersed waves have been identified and extracted. Synthesis of the abovementioned harmonic components can provide a reliable estimate of the rocking (torsional) motion induced by an (extracted) Rayleigh (Love) wave.We apply the proposed angular displacement estimation procedure for two well recorded data sets: (1) the strong motion data generated by an aftershock of the 1999 Chi-Chi, Taiwan earthquake and recorded over the Western Coastal Plain (WCP) of Taiwan, and (2) the strong motion data generated by the 2010 Darfield, New Zealand earthquake and recorded over the Canterbury basin. The former data set is dominated by basin-induced Rayleigh waves while the latter contains primarily Love waves.     

MODELLING CHANNEL WAVES WITH SYNTHETIC SEISMOGRAMS IN AN ANISOTROPIC IN-SEAM SEISMIC SURVEY1

In-seam seismic surveys with channel waves have been widely used in the United Kingdom and elsewhere to map coal-seams and to detect anomalous features such as dirt bands, seam thinning and thickening, and particularly in-seam faulting. Although the presence of cleat-induced anisotropy has been recognized in the past, almost all previous analyses have assumed homogeneous isotropic or transversely isotropic coal-seams. Channel waves, however, exhibit properties which cannot be fully explained without introducing anisotropy into the coal-seam. In particular, Love-type channel waves are observed for recording geometries where, in a homogeneous isotropic or transversely isotropic structure, the source would not be expected to excite transverse motion. Similarly, modes of channel-wave propagation display the coupled three-component motion of generalized modes in anisotropic substrates, which would not be expected for Rayleigh and Love wave motion in isotropy or in transversely isotropic media with azimuthal isotropy. We model the observed in-seam seismic channel waves with synthetic seismograms to gain an understanding of the effects of cleat-induced anisotropy on the behaviour of channel waves. The results show a reasonable good match with the observations in traveltime, relative amplitudes, dispersion characteristics and particle motions. We demonstrate that anisotropy in the surrounding country rocks contributes significantly to the coupling of channel wave particle motion, although its effect is not as strong as the anisotropy in the coal-seam. We conclude that the effects of cleat- and stress-induced anisotropy are observed and can be modelled with synthetic seismograms, and that anisotropy must be taken into account for the detailed interpretation of channel waves.     

PARAMETER ESTIMATION AND FAULT DETECTION BY THREE-COMPONENT SEISMIC AND GEOELECTRICAL SURVEYS IN A COAL MINE*

Three-component seismic and geoelectrical in-mine surveys were carried out in Lyukobanya colliery near Miskolc, Hungary to determine the in situ petrophysical parameter distributions and to detect inhomogeneities in the coal seam. The seismic measurements comprise an underground vertical seismic profile, using body waves, and an in-seam seismic amplitude-depth distribution and transmission survey, using channel waves. The geoelectrical measurements are based on the drift- and seam-sounding method. Interval traveltime-, amplitude-, multiple-filter- and polarization analysis methods are applied to the seismic data. They lead to a five-layer model for the strata including the coal seam. The coal seam and two underlying beds act as a seismic waveguide. The layer sequence supports the propagation of both normal and leaky mode channel waves of the Love- and Rayleigh type. A calculation of the total reflected energy for each interface using Knott's energy coefficients shows that the velocity ranges of high reflection energy and of normal and leaky mode wavegroups coincide. The excitation of wavegroups strongly depends on the seismic source. A simultaneous inversion of a geoelectrical drift- and seam-sounding survey prevents misinterpretations of the seismic data by clearly identifying the low-velocity coal seam as a high-resistivity bed. Calculations of dispersion and sounding curves improve the resolution of the slowness and resistivity in each layer. Both diminished amplitudes and distortions in the polarization of transmission seismo-grams and decreasing resistivities in a geoelectrical pseudosection of the coal seam are related to an inhomogeneity. A calculation of synthetic seismograms for Love and Rayleigh channel waves with the finite-difference and the Alekseev-Mikhailenko method agrees well with the field data for the main features, i.e., particular arrivals in the wave train, wavegroups, velocities and symmetries or asymmetries. This in-mine experiment demonstrates that the simultaneous acquisition, processing and interpretation of seismic and geoelectrical data improve the lithological interpretation of petrophysical parameter distributions. Coal seam inhomogeneities can also be detected more reliably by the two independent surveys than by one alone.     

有限元算法在声波方程数值模拟中的频散分析

针对有限元算法在地震波数值模拟中的数值频散问题,利用集中质量矩阵双线性插值有限元算法,推导了二维声波方程的频散函数.在此基础上采用定量分析方法,对比分析了网格纵横长度比变化时的入射方向、空间采样间隔、地震波频率以及地层速度对数值频散的影响.数值算例和模型正演结果表明:当采用集中质量矩阵双线性插值有限元算法时,为了有效地压制数值频散,在所使用震源子波的峰值频率对应的波长内,采样点数目应不少于20个;减小网格长度的纵横比可以有效地抑制入射角(波传播方向与z轴的夹角)较小的地震波的数值频散;地震波频率越高,传播速度越慢,频散越严重,尤其是当相速度与其所对应的频率比值小于2倍空间采样间隔时,不仅会出现严重的数值频散,还会出现假频现象.      

煤矿井下槽波三维数值模拟及频散分析

采用交错网格高阶有限差分法编制了地震波场三维正演模拟软件,设计了基于镜像法原理处理煤矿井下近水平和起伏巷道特殊空间的算法;模拟了煤矿井下含巷道和不含巷道情况下煤层中传播的地震波场,并分析其频散特征.结果发现:由于巷道的影响,巷道壁上产生很强的巷道振型槽波,煤层中则出现了以Love型为主的槽波,据此分析了实际槽波记录的形成机理,研究结果对今后煤矿井下巷道地震超前探测和工作面弹性波透视等具有重要的理论意义和实际价值.     

Automatic pickup of arrival time of channel wave based on multi-channel constraints

Accurately detecting the arrival time of a channel wave in a coal seam is very important for in-seam seismic data processing. The arrival time greatly affects the accuracy of the channel wave inversion and the computed tomography (CT) result. However, because the signal-to-noise ratio of in-seam seismic data is reduced by the long wavelength and strong frequency dispersion, accurately timing the arrival of channel waves is extremely difficult. For this purpose, we propose a method that automatically picks up the arrival time of channel waves based on multi-channel constraints. We first estimate the Jaccard similarity coefficient of two ray paths, then apply it as a weight coefficient for stacking the multichannel dispersion spectra. The reasonableness and effectiveness of the proposed method is verified in an actual data application. Most importantly, the method increases the degree of automation and the pickup precision of the channel-wave arrival time.     

基于波场垂向和水平方向外推的高陡构造偏移

常规的单程波波动方程偏移成像方法对大角度的高陡构造偏移成像存在内在的限制.根据波动方程在各个空间方向的数学特性和高陡构造反射地震波的传播特征,通过把地震波分解为垂向的上下行波、水平方向的前后行波和左右行波,提出基于波场垂向外推和水平方向外推相结合的单程波波动方程高陡构造偏移成像方法,即用波场垂向外推的单程波波动方程偏移成像方法解决中低角度平缓构造的偏移成像,用波场水平方向外推的单程波波动方程偏移成像方法解决中高角度陡倾构造的偏移成像.这种基于波场垂向和水平方向外推相结合的高陡构造偏移成像方法是常规单程波波动方程叠前深度偏移成像方法的补充和改进,它相对基于全波方程的逆时偏移具有计算效率上的优势.     

地震槽波的数学-物理模拟初探

针对地震槽波在低速层的传播特性,开展了煤层内地震槽波勘探的数值模拟和物理模拟研究的初探工作.在数值模拟研究方面,采用交错网格有限差分法对煤层中的地震槽波进行三分量全波场模拟.基于波场快照和人工合成地震记录研究了不同模型中的波场特征和各种波型的传播规律.在物理模拟方面,通过选用不同配比的环氧树脂和硅橡胶类材料构建地震槽波物理模型,利用透射法和反射法观测系统获得了清晰的地震槽波记录以研究槽波的地震学特征.研究表明,在煤层内槽波的地震波场中,Love型槽波的能量小于Rayleigh型槽波的SV分量,大于Rayleigh型槽波的SH分量.相对于Love型槽波和Rayleigh型槽波的SH分量,Rayleigh型槽波的SV分量在围岩中的泄露能量较强.在煤层界面附近的围岩中,地震波仍以槽波形式传播,随着距离的增加能量逐渐衰减.随着煤层变薄,煤层槽波主频向高频方向移动,频散现象增强,传播速度增大.     

SV波全反射作用下地震动的合成及振动特性

越来越多的研究表明来自基岩的地震波并不是垂直地面向上传播的。地震波在斜入射与垂直入射时所产生的场地效应有很大不同,由于存在全反射现象,SV波在斜入射时产生的场地效应更为复杂。文章基于均匀弹性半空间地震波传播理论,分别推导得到SV波入射角在小于、大于等于临界角时地震动的计算表达式,通过模型算例研究SV波全反射作用下的地震动特性。研究发现：由SV波产生的地震动主要由入射波和反射波构成,滑行波作用可以忽略;地面运动轨迹具有面波旋转振动特点;随着入射角的增大,地面震动从以水平方向振动为主逐渐过渡到以垂直方向振动为主,两个方向的振动均小于入射波峰值的2倍。     

关于一种新型横波震源（SH型）的探讨

实现横波（SH波）勘探的关键问题是震源。现有的SH波震源--扭力振动器的缺点是辐射方向性不好,能量集中在水平方向,而在垂直方向辐射的能量几乎为零,这样的震源对于反射波勘探是不利的。 本文从理论上提出用垂直力矩构成横波震源。理论推导结果（高频渐近解）表明,该震源在方位角θ=90°方向上辐射纯SH波,SH波能量辐射集中在垂直方向,而在水平方向几乎为零。显然,这样的震源对于反射波勘探十分有利。 文中还采用Cagniard-deHoop回路积分技术计算了波场的精确解及最大振幅随离源角的变化,结果与解析解一致.     

基于Poynting矢量行波分离的最小二乘逆时偏移

因为在逆时偏移中基于双程波动方程构建震源波场和检波器波场,所以在波场延拓过程中地震波遇到波阻抗界面时,背向发育的反射波会与正常传播的波场互相关产生较强振幅的低频噪声.这一特点使得以逆时偏移为基础的最小二乘偏移方法在梯度计算时同样存在着低频噪声的干扰,从而导致反演收敛的速度减慢.考虑到计算量和存储成本的因素,本文借助Po...     

Love waves in an inhomogeneous fluid saturated porous layered half-space with linearly varying properties

The paper is concerned with the propagation of the Love waves in an inhomogeneous transversely isotropic fluid saturated porous layered half-space with linearly varying properties. The analysis is based on Biot's theory. Firstly, the dispersion equation in the complex form for the Love waves in an inhomogeneous porous layer is derived. Then the equation is solved by an iterative method. Detailed numerical calculation is presented for an inhomogeneous fluid saturated porous layer overlying a purely elastic half-space. The dispersion and attenuation of the Love waves are discussed. In addition, the upper and lower bounds of the Love wave speed are explored.     

Crustal structure beneath Liaoning province and the Bohai Sea and its adjacent region in China based on ambient noise tomography

The velocity structure of the crust beneath Liaoning province and the Bohai sea in China was imaged using ambient seismic noise recorded by 73 regional broadband stations. All available three-component time series from the 12-month span between January and December 2013 were cross-correlated to yield empirical Green's functions for Rayleigh and Love waves. Phasevelocity dispersion curves for the Rayleigh waves and the Love waves were measured by applying the frequencytime analysis method. Dispersion measurements of the Rayleigh wave and the Love wave were then utilized to construct 2D phase-velocity maps for the Rayleigh wave at8–35 s periods and the Love wave at 9–32 s periods,respectively. Both Rayleigh and Love phase-velocity maps show significant lateral variations that are correlated well with known geological features and tectonics units in the study region. Next, phase dispersion curves of the Rayleigh wave and the Love wave extracted from each cell of the 2D Rayleigh wave and Love wave phase-velocity maps,respectively, were inverted simultaneously to determine the3 D shear wave velocity structures. The horizontal shear wave velocity images clearly and intuitively exhibit that the earthquake swarms in the Haicheng region and theTangshan region are mainly clustered in the transition zone between the low-and high-velocity zones in the upper crust, coinciding with fault zones, and their distribution is very closely associated with these faults. The vertical shear wave velocity image reveals that the lower crust downward to the uppermost mantle is featured by distinctly high velocities, with even a high-velocity thinner layer existing at the bottom of the lower crust near Moho in central and northern the Bohai sea along the Tanlu fault, and these phenomena could be caused by the intrusion of mantle material, indicating the Tanlu fault could be just as the uprising channel of deep materials.     

三角网格有限元法波动模拟的数值频散及稳定性研究

三角网格有限元法能够准确模拟复杂构造和复杂介质条件下的地震波场,数值频散和稳定性条件是地震波数值模拟中参数选择的主要依据.基于均匀的线性三角网格单元,根据结构刚度矩阵的组装原理以及平面波理论,推导了集中质量矩阵下两种网格结构的声波频散函数以及稳定性条件,并对数值频散特性以及稳定性进行了详细研究:三角网格单元中波动的数值频散除了受到空间采样间隔、单元网格纵横比和波传播方向等常规因素的影响外,还受到网格布局的影响,过锐或过钝的三角单元会对波动数值频散产生不良的影响,不同类型的单元网格、单元纵横比对应着不同的稳定性条件,正三角单元中的波动具有较好的数值频散特性,其数值各向异性(频散随波传播方向的变化)效应最弱,稳定性条件也较为宽松.最后通过数值模拟直观地验证了以上分析结果,为有限元正演三角网格的剖分和参数的设置提供一定的理论依据.     

CALCULATION OF DISPERSION CURVES AND AMPLITUDE-DEPTH DISTRIBUTIONS OF LOVE CHANNEL WAVES IN HORIZONTALLY-LAYERED MEDIA*

We present dispersion curves, and amplitude-depth distributions of the fundamental and first higher mode of Love seam waves for two characteristic seam models. The first model consists of four layers, representing a coal seam underlain by a root clay of variable thickness. The second model consists of five layers, representing coal seams containing a dirt band with variable position and thickness. The simple three-layer model is used for reference. It is shown that at higher frequencies, depending on the thickness of the root clay and the dirt band, the coal layers alone act as a wave guide, whereas at low frequencies all layers act together as a channel. Depending on the thickness, and position of the dirt band and the root clay, in the dispersion curves of the group velocity, secondary minima grow in addition to the absolute minima. Furthermore, the dispersion curves of the group velocity of the two modes can overlap. In all these cases, wave groups in addition to the Airy phase of the fundamental mode (propagating with minimum group velocity) occur on the seismograms recorded in in-seam seismic surveys, thus impeding their interpretation. Hence, we suggest the estimation of the dispersion characteristics of Love seam waves in coal seams under investigation preceding actual field surveys. All numerical calculations were performed using a fast and stable phase recursion algorithm.     

STUDIES OF ROADWAY MODES IN A COAL SEAM BY DISPERSION AND POLARIZATION ANALYSIS: A CASE HISTORY*

Field data from two-component in-seam seismic measurements are used to study roadway modes and their interaction with reflected seam waves. Using the multiple-filter technique to investigate the dispersion behaviour of the different waves, it can be shown that the roadway modes disperse very similarly to the related transmitted seam waves. However, because of the free surface of the coal face, the dispersion curves of the roadway modes show a velocity reduction and a slight shift to lower frequencies compared to those of the related transmitted seam waves. Polarization analysis using hodograms, rectilinearity and polarization angle confirms these results. The parameters found by polarization analysis can be used to design polarization filters which help to separate roadway modes and reflected events in the traveltime range of superposition in the presented field case.     

Inversion of SASW dispersion curves based on maximum flexibility coefficients in the wave number domain

Spectral analysis of surface waves (SASW) is a nondestructive in-situ testing method that is used to determine stiffness profiles of soil and pavement sites based on dispersion characteristics of Rayleigh-type surface waves.Inversion of the Rayleigh wave dispersion curve of a site provides information on the variation of shear-wave velocity with depth. In the inversion procedures currently used for SASW tests, the field dispersion curve is matched with a theoretical dispersion curve obtained for the fundamental mode of surface wave propagation.In order to overcome difficulties associated with the presence of multi-modes in SASW signals, a new inversion method based on the maximum vertical flexibility coefficient is introduced in this paper. Unlike root-searching methods, the new method easily identifies the predominant propagation modes. In this new approach, the simplex method is used to match field and theoretical dispersion curves automatically. The purpose of this paper is to present the details of the new method and to demonstrate its advantages.     

考虑地震波激振方向的浅埋偏压双联拱黄土隧道动力响应规律研究

以实际工程为背景,在模型试验结果和数值模拟结果验证合理的基础上,通过建立三维数值模型,研究兰州人工波在不同激振方向下坡-隧体系动力响应规律,通过小波包变换从能量和频域角度对衬砌结构动力响应规律进行分析。研究结果表明：水平、竖直面内垂直隧道轴向(X、Z)的地震波在隧道最大埋深处引起较大响应,水平面平行于隧道轴向的地震波(Y)对埋深较浅的洞口处的结构最为不利。频率在0～12.5 Hz范围内的低频波是引起隧道结构响应的主要波段,该频段中竖直向地震波(Z)能量相较于其他方向地震波能量占比最高。地震作用中衬砌结构的存在对坡体内的围岩变形有一定的抑制效应。X、Y向地震波容易引起坡脚附近的围岩发生剪切破坏,Y向地震波对隧道洞口段仰坡的稳定性影响最大;Z向地震波容易造成坡顶附近区域围岩的拉伸破坏,且对隧道拱顶附近产生最不利响应。研究成果对浅埋偏压双联拱隧道的抗震优化设计具有借鉴意义。