【作者】 王雪秋；

【导师】 孙建国；

【作者基本信息】 吉林大学 ， 地球探测与信息技术， 2009， 博士

【摘要】 本文的研究工作主要有两方面:任意起伏地表地震波数值模拟技术及近地表地震波场的传播特征和响应规律研究。在地震波的数值模拟方法中,分析和讨论了能够处理起伏地表自由边界条件的广义虚像法,构建了具有与内部介质模拟精度和阶数同步的高阶广义虚像法差分边界条件方程,分析了其在应用中的局限性,使其与地表条件充零法联合使用,使其在任意地表起伏模型中都能够应用;实现了完全弹性介质模型、粘弹性介质模型和横向各向同性介质模型的起伏地表情况下的地震波波场数值模拟。通过数值模拟得到了不同模型,不同介质的地震波场传播和地震合成记录,通过整理和分析得到了如下认识:在复杂近地表模型条件下,地形严重扭曲了地下波场的形态,并造成了波场的不可识别;水平自由界面情况下,面波和表层多次波是近地表干扰的主要因素,地表严重起伏情况下,二次绕射形成的侧反射波的干扰要强于面波;通过合成记录的频谱分析可以看到,地形对地震波场有一定的选频作用,突起模型的效果比较明显,对具有频率效应的介质如粘弹性介质作用的表现更加明显;地形的起伏对地震波场响应不会产生频散,也就是说地形影响不具有频散特征,同时由于地形的影响,介质类型所产生的频散特征也不是很明显。也就是说地形起伏造成的能量散射或反射都是高能量的无频散的,通过某个频带的滤波效果是不可预期的。更多还原

【Abstract】 Modeling and understanding the effect of seismic wave propagation involving the complex near surface in West China has been one of the important issues in seismic exploration. In fact, the earth’s free surface is rugged topography at complex free surface condition areas. So based on the conditions the exact solution can not get. But this is usually the location at which seismic observations are made, topography may have a significant influence on record data. In fact at complex free surface areas, such as some classical topography model in West China, the research of the construction of recorded data is more slowly than the practice of exploration.Generally the complex free surface has included rugged topography and variation of velocity in lateral near free surface rock layer or soil layer. Professor Sun Jianguo has given a generally summary which included arbitrary combination three as down lines is complex free surface. And the three down lines are : (1) the earth’s free surface topography;(2) the complex geological construction near free surface;(3) the complex media and rock physical parameters distribution near free surface. For exact geological solutions from the observation seismic data, we must do the modeling of seismic wave field.The use of synthetic seismograms is one of most useful methods in estimating the response of media at a given receiver. Various numerical approaches have been proposed to solve the seismic wave equations. I present synthetics of seismic wave propagation near free surface topography. Based on existing direct and imaging methods of a 10th order staggered finite-difference scheme, an improved algorithm for staggered finite-difference is proposed to implement rugged topographic free boundary conditions. This method assumes that the free surface can be implemented with horizontal and vertical free surface segments and their corners. Based on the same principle, the method is adapted to elastic wave equations, visco-elastic wave equations and isotropic elastic wave equations.Main research contents in the article include:(1) The construction of mathematical physical model;(2) Synthetics of seismic wave propagation near free surface topography;(3) The influence of free surface topography through the seismic wave modeling;(4) The influence of the type of media through the seismic wave modeling;(5) The influence of the distribution of rock physical parameters near free surface through the seismic wave modeling;(6) The influence of some seismic parameters by the wave modeling. And by the work of this thesis, I get some conclusions in two fields about the development of modeling computation technology and some features of seismic wave propagation.In computation technology, I use high-order staggered grid finite difference method to solve the seismic wave equations. This is a ripe method of seismic modeling. And my key work is to develop the combination method general imaging method with zero velocity method to deal with the topography. Besides the elastic media seismic wave equations, the method is adapted to many other earth models, such as isotropic media, visco-elastic media and so on. And it can be used in 3D computations.By the modeling of seismic wave propagation, some features are drawn:(1) In all effect factors of complex near surface, the topography is the most one, and the second one is the distribution of rock physical parameters near free surface;(2) The ratio of signal/noise of cave model’s response is more better than of apophasis model;(3) Besides the distortion in x-axis of symmetry by the topography, it also does the distortion in z-axis of symmetry by the asymmetric topography; (4) The topography may be choose some frequencies to absorb;(5) The dispersion by topography is not obvious, so it isn’t to expect filtering the influence by topography.更多还原