Three-Dimensional Wavefield in a Two-Dimensional Basin Structure due to Point Source.

Three-dimensional wavefield in a two-dimensional sedimentary basin is calculated by using the direct boundary element method and the characteristics of the wavefield are considered.The first derivatives with respect to the source coordinates of the Green's functions are calculated, which are basic functions to consider the wavefield excited from fault sources.Expressing the wavefield in the basin by the superposition of waves from the sources that are distributed on the basin-basement boundary and separating the Green's functions which express the contributions from distributed sources into the SH-wave part and the P-SV-wave part, we can separate the wavefield in the basin into the SH-wave part which consists of the SH-waves from the distributed sources on the boundary and the P-SV-wave part.In this separation, Love waves that are secondarily excited in the basin are included in the SH-wave part and Rayleigh waves excited in the basin are included in the P-SV-wave part.Furthermore, dividing the boundary into the positive part of the x-component from the observation point and the negative part, we can separate the wavefield into the part which consists of the waves whose x-component of the velocities have positive values and the part which consists of the waves whose x-component of the velocities have negative values.