【作者】 邢庆祝；

【导师】 黄真萍；

【作者基本信息】 福州大学 ， 环境岩土工程， 2005， 硕士

【摘要】 地震CT(层析成像)是一种通过分析观测到的穿过地球内部的地震波的运动学和动力学特征,获得地震的破裂过程以及沿射线路径上介质物性信息的重要的地球物理方法。根据不同的研究目的和需要,既可以利用天然地震也可以借助于人工地震来获得不同深度的地球介质的分层或构造图像。地震波正演模拟技术作为地震CT实现的关键一步,它的精度与实现效率直接影响着地震CT的成像效果,因此加强地震波正演模拟技术研究至关重要。基于此,本文作者在对现有正演方法进行研究基础上,提出一种新的正演模拟方法(动态扫描法),并编制了实现该方法的程序。通过动态扫描法的试算,并与解析解的比较,动态扫描法的总体误差达到10-6s;又与最短路径法进行了对比,动态扫描法相对误差的均方差在1.5以下,而最短路径法相对误差的均方差在25以上。在对动态扫描法进行验证,认为具有较高精度的基础上,利用该方法分别对不同地层模型内地震波的传播从时间领域和空间领域进行了模拟,结果基本与事实相符。并用该方法模拟了井间CT观测系统下地震波初至规律,建立了地震波初至与深度的关系式,实现了地震波波前对模型异常体的识别模式。除此之外,本文还研究了近地表连续介质的几种速度分布函数以及变速介质中地震波传播规律,并推出了速度随深度线性变化介质的射线路径和波前面方程,为变速介质地震波的正演奠定了理论基础;总结了现有正演方法,并从基本原理到计算机实现过程进行了详细的论述;对经典试射法程序进行了编制与调试,成功实现了对反射波的正演模拟。本文的主要创新点:实现了高精度的动态扫描法在井间层析成像观测系统下地震波初至的模拟过程;提出和实现了采用地震波波前对异常体的识别方法和采用正演方法建立初至与深度关系式的方法。更多还原

【Abstract】 The seismic Computerized Tomography is one of an important geophysics technology utilized to obtain the medium information in the course of wave breaking process of the earthquake and on the ray route by analyzing kinematics and dynamics characteristic of seismic wave while penetrating through the earth. The medium information in different depth of the earth can be obtained either by natural earthquake or by artificial earthquake according to different researching purposes and needs. But the observing precision and realizing efficiency of seismic Computerized Tomography is directly influenced by the forward modeling technology of seismic wave which is a key step in the processing course of CT observation and it is essential to focus the study on the forward modeling simulation technology of seismic wave. Based on existing methods, a new kind of forward modeling simulation method, the dynamic scanning method, is proposed and realized by the developing of the forward modeling system. By comparative study, the global error of dynamic scanning method is about 10-6s, the mean deviation of relative error for dynamic scanning method is under 1.5 which is less than that of the shortest path method more than 25. Based on the high accuracy, separately imitating the spread of seismic wave in different geological model inland from time field and space field, its result is in conformity with fact basically. Under observation system of cross-well CT, the first break rule of seismic wave is simulated and the relational expression between the first break and the depth is established. In addition, the unusual body in the model is identified by seismic wave-fronts. Except for the above-mentioned works, the researches on several velocity functions of near-surface layer with <WP=5>variable velocity and seismic wave propagation law have been completed. Equations of wave-front and ray-paths in a continue velocity medium with vertical as well as horizontal velocity gradients are deduced which prepare the theoretical basis for the subsequent forward problems of first arrival times. The basic principles of all forward modeling methods and their processing courses are discussed and based on these methods the dynamic scanning method is proposed. The forward modeling of the reflection wave is completed on the basis of the computerized processing system developed for the classical ray method.The mian initiative of this paper: under observation system of cross-well CT, the simulating process of the first break rule of seismic wave is achieved by accurate dynamic scanning method, and the methods, which identifying the unusual body in the model by seismic wave-fronts and establishing the relational expression between the first break and the depth by the forward modeling, is proposed and realized.更多还原