SPATIAL VARIATIONS AND DIRECTIONALITY OF GROUND MOTIONS FOCUSED ON IRREGULAR UNDERGROUND STRUCTURE

Spatial variations and ground motion directionality in two horizontal directions focused on the irregular underground structure is investigated. During the ۱۹۹۴ Sanriku Haruka oki earthquake, the amplification from Hachinohe ۱MA (JMA) located on the rock site to Hachinohe City Hall (HCH) located on sediment site showed strong directionality, especially the NS component at HCH was largely amplified at axound ۱ Hz compared to ENV one. To explain the phenomena, the authors perform wave propagation analysis for an assumed two-dimensional soil model. The spatial variations and ground motions directionality due to the effect of the underground irregularity are discussed. The analytical results show that this amplification is due to the constructive interference of basin-induce surface waves (Love wave) and body waves (SH-wave) including refracted waves