Abstract
The 1995 Hyogo-ken Nanbu earthquake of JMA magnitude 7.2 caused serious damage widely throughout the Hanshin and Awaji areas in the Kinki district of southwest Japan . Damage to artificial structures was observed widely, even in the Osaka area 30-50 km east of the epicenter. Most of the damage was accompanied by ground failures such as liquefaction, lateral spreading and landslides of reclaimed lands along the coastal zone and river channels and ponds in the inland areas . Damage to artificial structures not accompanied by ground failure was also observed in several areas. Most of this type of damage was concentrated in narrow zones along the Butsunenji-yama fault and the Uemachi fault trending in the N-S direction . As the concentration of damage suggests that seismic waves were strongly amplified in limited zones around faults, we examined the focusing effect of seismic waves as one of possible interpretation . A velocity structure model composed of four homogeneous layers with curved interfaces referring to the result of a seismic reflection survey was utilized for this purpose. Two-dimensional calculations of wave paths and surface amplitudes support the possibility that vertical displacement of a subsurface geologic structure along the fault caused seismic waves to focus at the margin of the subsided block, resulting in the narrow zone of damage.
