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

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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.