Many structures were damaged in the vicinity of the epicenter, including Kobe-city and Ashiya-city, and severe damage occurred along an east-northeast trending narrow zone, so-called “the linear earthquake damage zone.” Structure damage also extended sporadically farther to Itami-city, Takarazuka-city, Toyonaka-city and Osaka-city where seismic motion with more than 5 of Richter scale was recorded. The damage grade becomes smaller concentrically from the epicenter except the linear damage zone.
The occurrence of the narrow severe damage zone has been explained by several hypothesis, e. g. the possible movement of hidden active faults under sediment, geomorphologic effect, amplification of earthquake motion in surface soft sediment, contrast of load-proof strength of structures between damaged and undamaged area, deep geological structure, etc.
After the earthquake, deep geological investigations involving dynamic explorations have been performed. and seismic simulation has been carried out by several organizations, which revealed detailed geological structures and dynamic character of the basement. These results are going to lead a true cause of earthquake damages.
This chapter first clarifies that earthquake damages caused by the geomorphologic and geological structure. However detailed study on it has already been described in the interim report, so new data was straightened in this paper. Secondly, we focus target structure of the basement and it's particular physical properties from the investigation of geological and geomorphologic consideration and earthquake motion simulation. Finally relationships between damages in the distant places and geological structure, geological distribution and geotechnical characteristics were described.
