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目前从野外地震记录中提取优质资料细节的兴趣,已激发了对数字模型过程的研究,这种过程能产生复杂的地下几何形状以及任意的震源——接收点排列情况下的合成地震记录,在对于此目的有效的种种方法中,将二维波动方程用有限差分表达式代替具有特殊的优点,这种方法简单,可以容易地完成。它能自动地估计各种到达波的原有的相对振幅,包括转换波、瑞利波、从断层带来的绕射波以及首波的分布。试验了两种计算方案,一是所谓“匀质法”,(homogeneous formulation)在不同弹性介质之间的标准边界条件必须被明显地满足,另一是“异质法”(heterogeneous formulation)此时的弹性性质可以在有限差分网格的每一个格点上被规定,而边界条件被暗含地满足,两种情况下震源的恰当模拟都要求特殊的处理。对具有勘探意义的几种模型所计算的合成地震记录可以说明,这个方法将如何帮助解释员。这些例子也说明了有限差分法的各个辅助方面,其中包含诸如网格色散,模型边缘的人为反射,以及空间与时间步长的选择等。
The current interest in extracting high-quality material details from field seismograms has stimulated the study of digital modeling processes that can produce complex subsurface geometries and synthetic seismograms of any source-receiver arrangement, Among the various methods that are effective for this purpose, replacing the two-dimensional wave equation with a finite difference expression has the particular advantage that this method is simple and can be easily accomplished. It automatically estimates the original relative amplitudes of various arrival waves, including converted waves, Rayleigh waves, diffraction waves from faults, and the distribution of the first wave. Two calculation schemes were tested. One was the so-called “homogeneous formulation” where the standard boundary conditions for the different elastic media had to be clearly satisfied, and the other was the “heterogeneous formulation” The elastic properties can be specified at every grid of the finite difference grid, while the boundary conditions are implicitly satisfied. In either case, proper simulations of the source require special handling. Synthetic seismograms calculated for several models of exploration significance illustrate how this method can help interpreters. These examples also illustrate the various auxiliary aspects of finite difference methods, including such things as grid dispersion, artificial reflections at the edges of the model, and the choice of space and time steps.