【摘要】：在地下介質(zhì)中傳播的地震波具有各向異性和粘滯性特點(diǎn),主要表現(xiàn)為地震波的速度隨方向變化、縱橫波之間的耦合作用、橫波分裂、子波峰值延遲、地震波振幅衰減、波形變寬和波形畸變等現(xiàn)象。地震波場在各項(xiàng)異性介質(zhì)和黏彈介質(zhì)中傳播特征的模擬是地震學(xué)研究的重要課題之一,它對(duì)理論算法驗(yàn)證、波場識(shí)別以及野外觀測系統(tǒng)設(shè)計(jì)等流程具有指導(dǎo)作用。旋轉(zhuǎn)交錯(cuò)網(wǎng)格將經(jīng)典交錯(cuò)網(wǎng)格中的速度、位移、應(yīng)力、應(yīng)變波場分量和介質(zhì)參數(shù)重新分布,應(yīng)力分量、介質(zhì)參數(shù)和速度分量被分別放置在單元網(wǎng)格沿對(duì)角線的兩個(gè)頂點(diǎn)上,通過兩個(gè)對(duì)角線方向上的導(dǎo)數(shù)值近似水平和垂直方向上的導(dǎo)數(shù)。當(dāng)采用旋轉(zhuǎn)交錯(cuò)網(wǎng)格對(duì)地下介質(zhì)中傳播的地震波數(shù)值模擬時(shí),不需要對(duì)彈性模量進(jìn)行平均,該優(yōu)點(diǎn)在模擬地震波在孔隙介質(zhì)、各向異性介質(zhì)中傳播時(shí)克服了經(jīng)典交錯(cuò)網(wǎng)格計(jì)算不穩(wěn)定的缺點(diǎn),提高了波場模擬的精度。根據(jù)地震波各向異性傳播理論,傳播在地下介質(zhì)中的縱橫波是相互耦合的,由常規(guī)模擬方法得到的地震記錄和波場快照中同時(shí)含有擬縱波和擬橫波分量,成為單獨(dú)研究縱波或橫波在各向異性介質(zhì)中傳播特征的難點(diǎn)�？v橫波的耦合現(xiàn)象也為地下目標(biāo)體的精確成像(逆時(shí)偏移成像等)帶來困難。在各向異性介質(zhì)中,擬縱波和擬橫波的極化方向和地震波的傳播方向通常含有一個(gè)夾角。采用各向同性介質(zhì)中波場分離分解方法將不能將縱橫波場完全分離。本文采用將各向異性介質(zhì)中的多分量波場分別投影到擬縱波和擬橫波的極化方向上,使得在各向異性介質(zhì)中傳播的相互耦合縱、橫波場分離,獲得只含有單一波場的地震記錄和波場快照。本文采用旋轉(zhuǎn)交錯(cuò)網(wǎng)格高階有限差分技術(shù)對(duì)具有傾斜對(duì)稱軸的橫向各向同性(titled transverse isotropy,簡稱TTI)介質(zhì)中傳播的地震波進(jìn)行了正演模擬,并在旋轉(zhuǎn)交錯(cuò)網(wǎng)格下對(duì)地震波場進(jìn)行了波場分解處理,由于X和Z速度分量在相同位置,不需要對(duì)速度分量進(jìn)行平均和插值處理,減小了計(jì)算誤差和計(jì)算耗時(shí)。為了削弱人為邊界對(duì)研究區(qū)域波場的影響,本文采用了CE衰減邊界條件和完全匹配層吸收邊界條件。
[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.
【學(xué)位授予單位】：長安大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2015
【分類號(hào)】：P631.4

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相關(guān)期刊論文 前1條

1 陳浩;王秀明;趙海波;;旋轉(zhuǎn)交錯(cuò)網(wǎng)格有限差分及其完全匹配層吸收邊界條件[J];科學(xué)通報(bào);2006年17期

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本文編號(hào)：2500500