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在我国的西部地区,地震波场十分复杂,信噪比低。本文采用波动方程正演模拟的方法研究复杂波场的形成原因。在模拟物性差异较大介质中的地震波场时,密度的影响不可忽略,因此,本文用含密度项的声波方程的交错网格有限差分法模拟地震波场并进行分析。设计了一个具有起伏地表、低速覆盖层和高速地层出露的复杂构造,从瞬时波场分布分析了形成复杂波场的原因。低速层对地震波场的影响明显,低速层中产生很强的槽波,低速层顶底形成的多次反射向地下传播又形成了复杂的反射波场。为了验证波场模拟结果的可靠性,对模拟波场用与正演模拟不同的算法进行叠前深度偏移,得到了与已知构造相同的偏移叠加剖面。
In the western part of China, the seismic wave field is very complicated with low signal-noise ratio. In this paper, the formation of complex wavefields is studied by forward modeling of wave equations. In the simulation of seismic wavefields with large difference in physical properties, the influence of density can not be neglected. Therefore, the seismic wavefield is modeled and analyzed by the staggered-grid finite difference method with density term acoustic wave equation. A complex structure with undulating ground surface, low velocity overburden and high velocity formation is designed. The reason of complex wave field is analyzed from the distribution of instantaneous wave field. The effect of low velocity layer on the seismic wave field is obvious. Strong groove wave is generated in the low velocity layer. The multiple reflections formed at the top and bottom of low velocity layer form a complex reflection wave field. In order to verify the reliability of wavefield simulation results, prestack depth migration is performed on the simulated wavefield using a different algorithm than forward modeling to obtain the same offset superimposed profile as the known one.