TTI介质旋转交错网格波场数值模拟及波场分离
发布时间：2019-06-15 20:43
【摘要】：在地下介质中传播的地震波具有各向异性和粘滞性特点,主要表现为地震波的速度随方向变化、纵横波之间的耦合作用、横波分裂、子波峰值延迟、地震波振幅衰减、波形变宽和波形畸变等现象。地震波场在各项异性介质和黏弹介质中传播特征的模拟是地震学研究的重要课题之一,它对理论算法验证、波场识别以及野外观测系统设计等流程具有指导作用。旋转交错网格将经典交错网格中的速度、位移、应力、应变波场分量和介质参数重新分布,应力分量、介质参数和速度分量被分别放置在单元网格沿对角线的两个顶点上,通过两个对角线方向上的导数值近似水平和垂直方向上的导数。当采用旋转交错网格对地下介质中传播的地震波数值模拟时,不需要对弹性模量进行平均,该优点在模拟地震波在孔隙介质、各向异性介质中传播时克服了经典交错网格计算不稳定的缺点,提高了波场模拟的精度。根据地震波各向异性传播理论,传播在地下介质中的纵横波是相互耦合的,由常规模拟方法得到的地震记录和波场快照中同时含有拟纵波和拟横波分量,成为单独研究纵波或横波在各向异性介质中传播特征的难点。纵横波的耦合现象也为地下目标体的精确成像(逆时偏移成像等)带来困难。在各向异性介质中,拟纵波和拟横波的极化方向和地震波的传播方向通常含有一个夹角。采用各向同性介质中波场分离分解方法将不能将纵横波场完全分离。本文采用将各向异性介质中的多分量波场分别投影到拟纵波和拟横波的极化方向上,使得在各向异性介质中传播的相互耦合纵、横波场分离,获得只含有单一波场的地震记录和波场快照。本文采用旋转交错网格高阶有限差分技术对具有倾斜对称轴的横向各向同性(titled transverse isotropy,简称TTI)介质中传播的地震波进行了正演模拟,并在旋转交错网格下对地震波场进行了波场分解处理,由于X和Z速度分量在相同位置,不需要对速度分量进行平均和插值处理,减小了计算误差和计算耗时。为了削弱人为边界对研究区域波场的影响,本文采用了CE衰减边界条件和完全匹配层吸收边界条件。
[Abstract]:Seismic waves propagated in underground media have the characteristics of anisotropy and viscosity, such as the variation of seismic wave velocity with direction, the coupling between P-S waves, shear wave splitting, wavelet peak delay, seismic wave amplitude attenuation, waveform broadening and waveform distortion. The simulation of seismic wave field propagation characteristics in heterosexual media and viscous elastic media is one of the important topics in Seismology. It plays a guiding role in the verification of theoretical algorithm, wave field identification and field observation system design. The velocity, displacement, stress, strain wave field component and medium parameter in the classical staggered grid are redistributed in the rotating staggered grid. The stress component, the medium parameter and the velocity component are placed on the two points of the diagonal line of the element grid respectively, and the derivatives in the horizontal and vertical directions are approximated by the derivative values in the two diagonal directions. When rotating staggered grid is used to simulate the seismic wave propagating in underground medium, it is not necessary to average the elastic modulus. This advantage can overcome the instability of classical staggered grid calculation and improve the accuracy of wave field simulation when simulating the propagation of seismic wave in porous medium and anisotropic medium. According to the anisotropy propagation theory of seismic wave, the P-S wave propagated in underground medium is coupled with each other. The seismic record and wave field snapshot obtained by conventional simulation method contain both quasi-P-wave and quasi-shear wave components, which becomes a difficult point to study the propagation characteristics of P-wave or S-wave in anisotropic medium alone. The coupling phenomenon of P-S wave also brings difficulties to the accurate imaging of underground target (inverse time migration imaging, etc.). In anisotropic media, the polarization direction of quasi-longitudinal wave and quasi-shear wave and the propagation direction of seismic wave usually contain an angle. The longitudinal and transverse wave fields can not be completely separated by the wave field separation and decomposition method in isotropic media. In this paper, the multi-component wave fields in anisotropic media are projected onto the polarization direction of quasi-longitudinal waves and quasi-shear waves, respectively, so that the coupled longitudinal and shear wave fields propagated in anisotropic media are separated, and the seismic records and wave field snapshot with only a single wave field are obtained. In this paper, the high-order finite difference technique of rotating staggered grid is used to simulate the seismic wave propagated in transversely isotropic (titled transverse isotropy, (TTI) medium with inclined symmetrical axis, and the wave field is decomposed under rotating staggered grid. Because the X and Z velocity components are in the same position, it is not necessary to average and interpolation the velocity components, which reduces the calculation error and calculation time. In order to weaken the influence of artificial boundary on the wave field in the study area, the CE attenuation boundary condition and the perfectly matched layer absorption boundary condition are used in this paper.
【学位授予单位】：长安大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P631.4
本文编号：2500500
[Abstract]:Seismic waves propagated in underground media have the characteristics of anisotropy and viscosity, such as the variation of seismic wave velocity with direction, the coupling between P-S waves, shear wave splitting, wavelet peak delay, seismic wave amplitude attenuation, waveform broadening and waveform distortion. The simulation of seismic wave field propagation characteristics in heterosexual media and viscous elastic media is one of the important topics in Seismology. It plays a guiding role in the verification of theoretical algorithm, wave field identification and field observation system design. The velocity, displacement, stress, strain wave field component and medium parameter in the classical staggered grid are redistributed in the rotating staggered grid. The stress component, the medium parameter and the velocity component are placed on the two points of the diagonal line of the element grid respectively, and the derivatives in the horizontal and vertical directions are approximated by the derivative values in the two diagonal directions. When rotating staggered grid is used to simulate the seismic wave propagating in underground medium, it is not necessary to average the elastic modulus. This advantage can overcome the instability of classical staggered grid calculation and improve the accuracy of wave field simulation when simulating the propagation of seismic wave in porous medium and anisotropic medium. According to the anisotropy propagation theory of seismic wave, the P-S wave propagated in underground medium is coupled with each other. The seismic record and wave field snapshot obtained by conventional simulation method contain both quasi-P-wave and quasi-shear wave components, which becomes a difficult point to study the propagation characteristics of P-wave or S-wave in anisotropic medium alone. The coupling phenomenon of P-S wave also brings difficulties to the accurate imaging of underground target (inverse time migration imaging, etc.). In anisotropic media, the polarization direction of quasi-longitudinal wave and quasi-shear wave and the propagation direction of seismic wave usually contain an angle. The longitudinal and transverse wave fields can not be completely separated by the wave field separation and decomposition method in isotropic media. In this paper, the multi-component wave fields in anisotropic media are projected onto the polarization direction of quasi-longitudinal waves and quasi-shear waves, respectively, so that the coupled longitudinal and shear wave fields propagated in anisotropic media are separated, and the seismic records and wave field snapshot with only a single wave field are obtained. In this paper, the high-order finite difference technique of rotating staggered grid is used to simulate the seismic wave propagated in transversely isotropic (titled transverse isotropy, (TTI) medium with inclined symmetrical axis, and the wave field is decomposed under rotating staggered grid. Because the X and Z velocity components are in the same position, it is not necessary to average and interpolation the velocity components, which reduces the calculation error and calculation time. In order to weaken the influence of artificial boundary on the wave field in the study area, the CE attenuation boundary condition and the perfectly matched layer absorption boundary condition are used in this paper.
【学位授予单位】：长安大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P631.4
【参考文献】
相关期刊论文 前1条
1 陈浩;王秀明;赵海波;;旋转交错网格有限差分及其完全匹配层吸收边界条件[J];科学通报;2006年17期
，本文编号：2500500
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