Study on Time-Space Variations of Earthquake Waves Considering Non-Uniformity of Ground Surface Conditions

本研究的目的是阐明地面条件对地震动的影响。本研究考虑了不规则形状的地面，大量的树木和建筑物，它们在地面上有序地存在。即使先前已经指出具有不规则表面的地面可能引起复杂的地震响应，但是产生这种复杂响应的过程尚未被阐明。在本研究中，也对这一过程进行了探讨。例如，关于不规则地面的影响，指出了不规则地面会引起复杂的地震反应。然而，产生这种复杂反应的过程还不清楚。在本研究中，我们发展了边界元摄动法来研究不规则地表对地震波的散射。该方法基于频域边界元法和采用Neumann级数的摄动法。利用该方法，可以将地面反应分解为入射波和散射波引起的地面反应。数值结果表明，散射波的振幅受不规则表面到观测点的距离和方向的影响。

The purpose of this study is to clarify the effects of the conditions of the ground surface on the earthquake ground motions. Irregular shaped ground, lots of trees and buildings, Which are existing ordinally at the ground surface, were considered in this study. Even if it has been pointed out previously that the ground with an irregular surface may cause complicated seismic responses, the process of generating this complex response has not yet been clarified. In this study, such a process was also examined.Regarding the effects of the irregular ground surface, for example, it has been pointed out that the ground with an irregular surface causes complicated seismic responses. However, the process of generating this complex response is not yet clarified. In this study, boundary element-perturbation method has been developed to investigate scattering of seismic waves due to an irregular surface. This method is based on the boundary element method in frequency domain and perturbation technique employing the Neumann series. By using this method, the ground response can be separated into those induced by incident waves and scattered waves. Numerical results showed that the amplitudes of the scattered waves are affected by both distance and direction of the irregular surface to the observation points.