Analysys of building damage in Kashiwazaki city due to the 2007 Niigata-Ken Chuetu-Oki earthquake

This study investigates the building damage in Kashiwazaki city due to the 2007 Niigata-Ken Chuetsu-Oki, Japan earthquake. Most building fragility functions, used for damage estimation in scenario earthquakes in Japan, were developed based on the actual damage data from the 1995 Hyogoken-Nanbu (Kobe) earthquake. However, already sixteen years have passed after this event, and hence it is better to employ recent earthquake data. In this study, the damage ratios of buildings are investigated from the view points of structural material and the construction period. As a result, for wooden houses, the damage ratio gets higher as the construction period becomes older. It is clearly observed that within the construction period 1982-2007, the damage ratio becomes smaller for newer wooden houses. The reduction of damage ratio with construction period is also observed for other structural materials (RC and steel), but the ratios are much smaller than those for wooden houses. The spatial distribution of damaged buildings is further investigated with their position information on a geographic information system (GIS). The results are compared with the distribution of recorded peak ground velocity (PGV) values and the damage ratio is plotted comparing with the empirical fragility function from the Kobe earthquake. It is observed that the building damage ratios in the 2007 Niigata-Ken Chuetsu-Oki earthquake are lower than those from the Kobe earthquake.