多层介质地层中有低速层出现时的陷模研究

TRAPPED MODES IN MULTILAYERED MEDIA INCLUDEDA LOWVELOCITY FORMATION

在三维情况下，利用Ｂ，Ｐ，Ｃ坐标系研究了水平多层介质中导波的能量分布，提出了一种计算大深度处位移和能流密度的方法，避免了精度丢失问题。在有低速层介质情况下，在深入分析瑞利模的基础上，首次研究了陷模的频散及能流分布，分析了它们的传播机制。导波能量可能分布在自由表面附近，表现为面波；也可能集中在自由界面下某一深度处，表现为沿低速层延伸方向传播的导波。

The energy distributions of guided waves in multilayered media have been investigated in three dimensions in B, P, C coordinate system. A method of calculating the displacement and energy flux density at large depth was presented, and the problem of precision loss was avoided. In the case that a lowvelocity medium was included, not only was Rayleigh mode analyzed thoroughly, but also the dispersions and energy distributions of trapped modes were studied for the first time, and their mechanisms were analyzed. The energy of guided waves can concentrate possibly in a little area near the free surface, which is corresponding to the surface wave, and it also possibly concentrates in a depth under the free surface, which is corresponding to a guided wave propagation along the stretching direction of the lowvelocity formation.