【作者】 叶佩；

【导师】 李庆春；

【作者基本信息】 长安大学 ， 固体地球物理学， 2011， 硕士

【摘要】 地震波速度参数贯穿于整个地震数据采集、处理和解释流程,在地震勘探的每个环节中,速度均起着至关重要的作用。因此精确求取地震波在地下介质中的传播速度,直是地震勘探中值得深入研究的问题。地震旅行时层析成像是通过观测到的地震旅行时信息,应用模型重建算法反演地下介质结构、速度分布及弹性参数等重要信息的一种反演方法。地震旅行时层析成像问题是一个非线性反演问题,只利用单种波的旅行时信息进行反演不能够更准确、更全面的重构地下速度信息,因此尽可能的利用更多的地震数据信息进行反演一直是探索研究的方向。初至波易识别,易追踪,在井间地震或近地表速度分析及复杂地表静校正中,稳定性高,优势明显。与初至波旅行时相比,反射波携带地下更丰富信息,能够反映地下不同深度不同位置更精细尺度的结构和参数分布。因此,寻找一种有效的方法利用初至波和反射波旅行时进行联合层析,可以为高精度的地震勘探提供更稳定、更精确的速度分析。论文主要对地震初至波、反射波旅行时联合层析成像方法进行了研究,以此更精细的来建立中深层速度模型,为高精度地震勘探数据处理、解释提供速度信息。旅行时层析需要解决正演问题和反演问题。根据目前联合层析成像中较新的技术及其存在的问题,论文在正演中采用旅行时线性插值(LTI)射线追踪方法,反演采用LSQR法,针对正演方法的稳定性、计算精度、计算效率、功能扩展及反演中旅行时层析的混定特点,完成了部分技术改进。一、传统的LTI法在向前处理过程中没有考虑来自各个方向的射线,导致在横向速度变化剧烈的介质中,追踪出来的射线路径不满足最小旅行时。因此,本文对LTI法向前处理过程进行了改进,采用全方位循环的方法来计算各网格节点旅行时,通过模型测试验证了改进后的方法对复杂模型的适应性更强。二、LTI法是基于线性假设的,因此其计算精度与网格剖分的大小有关,但网格剖分太细又会增加计算耗时,为了保证LTI法的计算精度,同时保证计算效率,本文采用在网格边界插入次生节点的技巧,通过模型测试发现在网格剖分精度相同的情况下,加入次生节点的方法计算精度更高、耗时更短。三、LTI法是基于最短旅行时原理用于追踪初至波的,结合分区多步计算技术,提出了分区多步LTI法,该方法可以追踪二维复杂层状介质中的任意多次或一次透射、转换、反射波,通过模型试算及误差分析,验证了该方法具有误差收敛、数值稳定等特点,并且对复杂模型具有很强的适应能力,为多次波模拟提供了一种思路。四、针对旅行时层析成像中射线覆盖不均匀从而导致反演中Jacobi矩阵混定的特点,本文提出多尺度渐进反演策略,并在Jacobi矩阵中对模型参数进行加权及正则化处理,最后用LSQR法迭代求解,通过多组理论模型和实际资料试算及结果分析,验证了本文所采用方法的有效性及实用性。更多还原

【Abstract】 Seismic wave velocity is important during every procedure of seismic prospecting, including collection, processing and explanation of seismic data. Therefore, how to precisely get propagation velocity of seismic wave underground is one of the essential problems in seismic prospecting all the time.Seismic travel-time tomography is one of inversion method which can inverse important information of underground medium such as structure, velocity distribution and elastic parameter by reconstructing algorithm with models using seismic travel-time information collected. Seismic travel-time tomography is nonlinear inversion problem. Comprehensive velocity information can’t be obtained just through single wave inversion. So inversion with as more seismic information as possible has always been an important way sought by geophysicists. First-break has high stability and obvious advantages in velocity analysis of cross-hole or near surface and complex surface static move-out because it is easy to distinguish and trace while reflection wave can reflect deeper and finer structure and parameter distribution underground because of its strong energy with abundant underground information. Consequently, joint tomography with first-break and reflection travel-time is needed to provide more stable and precise velocity analysis for high-precision seismic prospecting. The main purpose of this paper is to construct mid-depth velocity model by the method of joint tomography with first-break and reflection travel-time, which can provide velocity information for data processing and explanation of high-precision seismic prospecting.Travel-time tomography is needed to resolve forward problerm and inversion problerm. In this paper, linear travel-time interpolation (LTI) ray tracing method is used in forward simulation, and LSQR method is adopted in reversion progress. We do reasearch about the calculation precision, calculation efficiency, function expansion in the forward simulation and mixed set feature of travel-time tomography in the inversion progress.1. In traditional LTI method, ray from different direction isn’t completely considered during tracing forward, which leads to traced ray path dissatisfy minimum travel-time in medium with strong transverse velocity variation. Calculating travel-time of each grid node by all-round cycle method during tracing forward is adopted in this paper. Model test shows that the improved method is more suitable for complex model.2. LTI method is based on linear assumption. Its precision depends on grid division. But calculation time become longer while the grid become smaller. In order to ensure both the precision and efficiency, new idea of inserting secondary nodes in grid boundary is put forward in this paper. It is proved by model test that the new method has higher precision and is less time consuming in the case of same grid division.3. LTI method traces first-break based on minimum travel-time theory. Multi-stage LTI method is proposed in this paper combining the improved LTI method with the multi-stage calculation technology, which can trace any multiple or single transmission wave as well as converted wave and reflection wave in two dimensional complex lamellar medium. The stability and precision of this method is checked by model test and error analysis. It provides a new way for multiple wave simulation.4. In order to solve the mixed set problem of Jacobi matrix during reversion caused by non-uniform ray covering in travel-time tomography, multi-scale gradual inversion method is raised, which weight and regularize model parameter in Jacobi matrix and then get the solution by LSQR iteration. It proves to be valid through multiple group model test and result analysis.更多还原