Behavior of the Elastic Waves Propagating through the Irregular Structures : III. Love Waves Propagating through the Nonhorizontal Structures

The characteristics of Love waves propagating through the laterally heterogeneous structures were studied using the finite element method. The waves generated by the transient excitation are identified as Love waves through the waveforms with depth, phase velocity, and amplitude characteristics. On the basis of these verifications, we have treated the following problems. First, we treated the problem of Love waves propagating the structure with a discontinuity. It was shown from a comparison of both Sato\u27s and Alsop\u27s solutions that the effects of body waves scattered at the vertical continuity are not negligible. In the case of the structure with a slant discontinuity, it was found that the smaller the slant angle of discontinuity the larger the amplitude of reflected Love waves. Secondly, the problem of Love waves propagating through a structure with a convexity was examined. It was found that the higher a convexity the larger the amplitude of reflected Love waves. The Love waves were formed anew after passing through the outcropped convexity. Furthermore, we studied the characteristics of Love waves propagating through the structures of the Tokyo metropolitan area from the viewpoint of an earthquake disaster counterplan. The finite element solutions for the models close to the real structures gave about a two-fold amplification at the period about 15 sec in the northern part of the 23 wards of Tokyo in comparison with the solutions assuming the horizontal layers. We are alarmed about the influence of such waves on the huge oil tanks and high rise buildings etc., which may have a longer natural period. We emphasize from the results of this study that it is very important to investigate the underground structures in detail