本文選題：波動方程 + 地震層析成像　； 參考：《清華大學》2016年博士論文

【摘要】：基于波動方程的層析成像方法被認為是研究地球內(nèi)部結(jié)構(gòu)和動力學過程的新一代成像方法。首先,本文利用伴隨方法、Born近似以及格林函數(shù)等發(fā)展了基于波動方程的地震層析成像和震源定位聯(lián)合反演方法。針對該方法需要求解正演波場和伴隨波場來計算層析成像的敏感核的問題,本研究提出了具有四階精度的高效率、低存儲需求、低數(shù)值頻散、易并行計算的三維近似解析中心差分方法,分析了其穩(wěn)定性和數(shù)值頻散關系,并針對不同的介質(zhì)模型給出了地震波傳播的波場模擬結(jié)果。GPU/CPU異構(gòu)并行加速試驗表明該方法具有優(yōu)良的并行加速效果。隨后,利用推導的差分方法在一個地殼-Moho面-地幔模型中計算了不同地震波震相,包括直達波、反射波、多次反射波以及首波的波形和走時敏感核。結(jié)果表明,無論是波形敏感核還是走時敏感核,都主要分布在以地震波傳播幾何路徑為中心的第一菲涅爾帶區(qū)域內(nèi);后續(xù)震相的敏感核不僅存在于第一菲涅爾帶,也包含反射點或散射點的等時線�；诓▌臃匠虒游龀上衩舾泻税葧r線是其能天然解決多路徑問題的原因之一。在應用方面,利用基于波動方程的走時層析成像對北京及其周邊區(qū)域地殼結(jié)構(gòu)進行層析成像研究。成像結(jié)果顯示該區(qū)域地殼的強非均勻性與地震的發(fā)生存在關聯(lián)性。唐山地震震中位置下方的低速異�？赡鼙砻髁黧w的存在;唐山地震及其余震的發(fā)生與流體對孕震層的弱化作用以及擴散、運移有關。在對美國南加利福尼亞Landers地震區(qū)域的層析成像研究中,嘗試了同時利用基于波動方程的層析成像方法和Moho反射震相對該區(qū)域整個地殼進行成像。檢測板測試結(jié)果表明Moho反射震相能夠顯著提高下地殼的層析成像結(jié)果分辨率。高分辨率成像結(jié)果揭示了近地表的非均勻性與地表地質(zhì)構(gòu)造有關;地震多發(fā)生于高速、低泊松比異常區(qū)域或者高低速異常交界區(qū)域。成像結(jié)果揭示的中下地殼中沿圣安德烈斯斷層東南端靠近索爾頓海槽存在明顯的低速異常,可能是巖漿擴張對地殼入侵和驅(qū)動作用導致下地殼存在流體所致;其北端的高速異常為含流體區(qū)域的邊界。在Big Bear地震震中下方存在一個高速P波,低速S波,高泊松比異常,該異常的形成可能與受上地幔中殘留的古法拉隆板塊下沉過程中對部分熔融的軟流圈物質(zhì)驅(qū)動所形成的低速異常對下地殼侵襲作用有關。
[Abstract]:The wave equation based tomography method is considered to be a new generation imaging method for studying the internal structure and dynamic processes of the earth. Firstly, the associated method born approximation and Green's function are used to develop seismic tomography and joint inversion method based on wave equation. In order to solve the problem that the forward wave field and the accompanying wave field need to be solved to calculate the sensitive core of tomography, this paper proposes a method with high efficiency, low storage requirement and low numerical dispersion with four order precision. A three-dimensional approximate analytical central difference method for parallel computation is presented, and its stability and numerical dispersion relationship are analyzed. The simulation results of seismic wave propagation in different media models are given. The parallel acceleration experiments of GPU / CPU show that this method has good parallel acceleration effect. Then, the seismic phases of different seismic waves, including direct wave, reflection wave, multiple reflection wave, first wave waveform and travel-time sensitive nucleus, are calculated in a crustal-Moho area-mantle model by using the derived difference method. The results show that both wave-sensitive nuclei and travel-time sensitive nuclei are mainly distributed in the first Fresnel zone centered on the geometric path of seismic wave propagation, and the subsequent seismic phase sensitive nuclei not only exist in the first Fresnel zone, but also in the first Fresnel zone. Isochronous lines that also contain reflection or scattering points. The inclusion of isochron in wave equation tomography is one of the reasons why it can solve multipath problem naturally. In application, the traveling time tomography based on wave equation is used to study the crustal structure in Beijing and its surrounding areas. The imaging results show that there is a correlation between the strong heterogeneity of the crust and the occurrence of earthquakes. The low velocity anomaly beneath the epicenter of the Tangshan earthquake may indicate the existence of the fluid, and the occurrence of the Tangshan earthquake and its aftershocks is related to the weakening, diffusion and migration of the fluid to the seismogenic layer. In the study of tomography in the Landers seismic region of Southern California, the method based on wave equation and the Moho reflection earthquake are used simultaneously to image the whole crust of the region. The measured results show that the Moho reflection phase can significantly improve the resolution of the tomography results of the lower crust. The high resolution imaging results reveal that the near surface heterogeneity is related to the surface geological structure, and the earthquakes mostly occur in the areas of high speed, low Poisson's ratio anomaly or the junction of high and low velocity anomalies. The imaging results reveal that there are obvious low-velocity anomalies in the middle and lower crust along the southeastern end of the San Andreas fault near the Solton trough, which may be caused by the intrusion and drive of magma to the crust and the existence of fluids in the lower crust. The high speed anomaly at the northern end is the boundary of the fluid-containing region. There is a high velocity P wave, low velocity S wave and high Poisson ratio anomaly below the Big Bear earthquake epicenter. The formation of the anomaly may be related to the invasion of the lower crust caused by the low-velocity anomaly driven by the partially melted asthenosphere material during the subsidence of the paleo-Faralon plate in the upper mantle.
【學位授予單位】：清華大學
【學位級別】：博士
【學位授予年份】：2016
【分類號】：O175
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本文編號：2034558