山前带地震数据的波动方程叠前深度偏移方法

作为复杂介质中最精确的地震波成像技术，波动方程叠前深度偏移在山前带复杂构造成像中大有可为，但该方法对速度误差非常敏感，抗噪能力较差，其成败取决于叠前去噪、表层速度结构反演和偏移速度分析的有效性，要使山前带地震勘探取得更大突破，就需改善单程波动方程深度偏移对高陡、倒转界面的成像精度，研究出可提高初至层析分辨率的新方法以及自地表开始的偏移速度建模方法。基于广角隐式有限差分单程波传播算子与波场“逐步累加”技术，研制了直接自起伏地表进行波场延拓与成像的叠前深度偏移算法。SEG山前逆掩推覆构造模型偏移试验表明，该算法具有很高的精度；川西龙门山实际宽线地震资料成像的试处理结果，也展示了该方法相对于叠后深度偏移的优势。研究还表明，面向地质目标优化地震波照明与接收效果也是需要重视的问题。

WAVE EQUATION PRESTACK DEPTH MIGRATION OF FOOTHILLS SEISMIC DATA

As the most accurate seismic imaging technique in complex media,wave equation prestack depth migration is suitable for imaging complex geological structures in foothills.However,the successful application of this method highly depends on effective prestack noise suppression,shallow velocity structure inversion,and migration velocity analysis,due to its high sensitivity to velocity error and its low noise immunity. In order to make a larger breakthrough in seismic exploration of foothills,it is necessary to enhance the accuracy of high gradient and inversion boundary imaging with one way wave equation,and to develop a new method for improving first break chromatography resolution and for migration velocity modeling from topography.Based on the frequency domain wide-angle implicit finite difference one way wave propagator,we develop an effective algorithm of prestack depth migration that directly performs wave field continuation and imaging from topography by using the strategy of "adding the recorded wavefields from the non-planar surface step by step when the depth coincides with the elevation of the receiver".Migration results of the SEG foothills overthrust model synthetic data shows that this approach is in high imaging accuracy.Migration of the real data acquired in Longmen Mountain on the northwest edge of the Sichuan Basin also verifies the advantage of prestack wave equation depth migration over the corresponding poststack depth migration.In addition,more attentions should also be paid to target-oriented optimization of seismic wave illumination and visibility.