人工源和随机源激发地震波的时域有限差分模拟研究

【作者】 彭菲；

【导师】 陈颙； 陈棋福； 刘澜波；

【作者基本信息】 中国地震局地震预测研究所 ， 固体地球物理， 2008， 硕士

【摘要】 地震波模拟是模拟地震波在介质中传播的一种数据模拟技术,是理解波在介质中传播的最有效方法。地震波数值模拟是探测地下结构的地震观测系统布设、资料采集、处理和解释等必不可少的重要环节,对于地震深部构造探测和地震场地条件调查,以及油气和矿产资源勘探等具有重要的科学意义。随着地震波理论和计算机技术的发展,现已形成以有限差分法、有限元法、伪谱法和积分方程法等现代地震波数值模拟技术。相对而言,交错网格有限差分法在综合性能(占内存大小、模拟精度、计算效率和并行算法实现)上是实用性最好的方法之一。本论文采用时域有限差分法,模拟探讨了炸药爆破和陆地气枪的人工源与环境噪声及各种微动信号导致的随机源激发的地震波信号特征,为采用近似点源的人工源地震测深方法分析瞬态的地震波场特征及探测提取地下目标体的空间分布特征及物性参数,及利用地脉动随机源探测方法从稳态/似稳态的波场中分析场地的地震动响应特性,提供正演模拟对比分析的参考依据。有限差分正演模拟采用有限大小的模型仿真无限大小的模型,需要对无限大小模型进行人工的截断,并在所建立的差分模型边界设置吸引边界用于吸收由于人工截断引起的假反射。本论文分析并实现了复频移-拉伸函数的完美匹配层(Perfectly Matched Layer, PML)吸收边界算法,实验模型结果表明该吸收边界算法计算稳定、效率高。在人工源地震测深数据资料实测与正演模型比对分析中,依据炸药震源进行探测的安新-宽城深地震剖面和气枪震源探测地下结构的上关湖水库实验的地壳结构反演结果,建立了分层的数值模拟模型,采用时域有限差分方法(finite difference time domain,即FDTD)模拟得到的合成理论地震图,与实际观测记录的主要震相匹配甚好,PML吸收边界条件能够有效模拟吸收边界处的地震波,模拟结果较传统的射线追踪合成记录有显著改善,表明了FDTD方法在模拟地震波传播方面的有效性和适用性。对于地脉动随机源模拟,基于地脉动探测的基本原理,分别建立了水平层状、倾斜层状、直立断层、正断层及逆冲断层五种由简单到复杂的模型进行模拟分析。对数值模拟获得的数据利用H/V谱比分析法(Nakamura方法)反演对比符合良好,表明FDTD的全波正演能很好的模拟获得各种模型在随机源激发下产生的稳定波场信息,为地脉动探测研究和应用提供了科学的依据。更多还原

【Abstract】 Numerical simulation technique is one of the most effective methods in understanding seismic wave propagation in complex media. It can be used in all steps in assisting seismic surveys for a variety of purposes, from survey design, all the way to the final stage of result interpretation. With the development of the seismic wave theory and the computer technology, numerical simulation using full-wave approaches such as finite difference, finite element, pesudospectral and integral equation methods have gained wide applications in many scientific and engineering fields.In general, based on the consideration of memory usage, accuracy, efficiency and parallel computation, the staggered grid finite difference method is reputed as one of the best methods. In this paper, the finite difference time domain (FDTD) method is used to discuss the characteristics of the seismic wave triggered by the artificial explosive and airgun sources and the random ambient noise and microtremors. The simulation results can provide a reference model for characterizing underground objects’distribution and material properties with the artificial quasipoint source sounding. It can also be used to study the seismic response caused by the static/quasi-static wave field due to random microtremor vibrations.FDTD technique models wave propagation in a finite domain, which is only a truncated portion of the real world. The absorbing boundary conditions are applied to absorb the unwanted reflection from the artificial truncation boundaries. In this thesis, the perfectly matched layer (PML) absorbing boundary condition using stretched coordinate function is adapted and implemented. The simulated results of the modeling cases discussed in this thesis have approved the superior stabilities and efficiencies of this algorithm.Based on the field seismic data acquired from the Anxin-Kuancheng deep seismic sounding profile and the inversion result of the crustal structure obtained from the research of the Shang Guan Lake reservoir underground structure using explosive and airgun sources, the simulated seismic waveforms are obtained with the finite difference time domain (FDTD) method. The simulation results match the recorded waveforms quite well in all main phases. The results are also compared with wave fields using traditional approaches. These results illustrated that FDTD method is highly effective and robust in simulating seismic wave propagation in complex tectionic structures.FDTD seismic wave simulations are also conduted for understanding the interaction of microtremor with 5 kinds of fundamental structures: they are horizontal layers, inclined layers, vertical fault, normal fault and reverse fault. The results match the inversion obtained from the H/V spectral contrast method (Nakamura method) very well, which means the FDTD method can also be a good simulation method to obtain the wave field information generated by random sources, and can provide valuable scientific insight for microtremor applications in earthquake engineering studies.更多还原