Trapped modes in multilayered media included a low-velocity formation

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.