Abstract:

Because the most used finite difference method to calculate wave propagation cannot handle irregular boundaries easily, a hybrid boundary element and finite difference method is proposed. Firstly, the boundary element method is used to obtain the wavefileds along a horizontal boundary which is going to be the boundary condition of the finite difference method in the next stop. Then the finite difference method is applied to obtain the wavefields under the interface. The wavefields are separated to vector P-wave and S-wave constituents, and considering the coherence of P-wave and S-wave in a conversion point, the image condition of cross-correlation between P- and S-waves is applied to obtain discontinuity image underground. Synthetic tests show the effectiveness of the proposed method.

Key words: irregular free-surface, boundary element method, finite difference method, passive source, reverse time migration

摘要：

为了在起伏自由边界条件下应用逆时偏移成像, 提出一种边界元与有限差分混合的方法来计算地震波场的逆时传播。首先, 使用边界元法反传地表台阵数据, 可以得到地下一水平界面上的波场位移数据; 然后, 将此水平面作为有限差分方法的边界, 并反传此水平面处的波形数据, 获得此水平面下空间的地震波场。为了应用成像条件, 利用地震波的性质, 将地震波场分离为矢量P波和S波成分, 对分离出的P波和S波分量, 应用互相关成像条件可获得地下界面。通过对理论数据的测试, 验证了方法的有效性。

关键词: 起伏地形, 边界元法, 有限差分法, 被动源, 逆时偏移成像