CHARACTERISTICS OF WEAK EARTHQUAKE GROUND MOTIONS IN THE SUMIYOSHI AREA OF KOBE

After the Hyogo-ken Nanbu earthquake of 1995, an array observation of aftershocks was done from north to south along the Sumiyoshi River in Kobe City. The degree of damage varied drastically following the river from north to south. The spectral ratio shapes for different sites wi thin the heavily damaged area were almost the same, suggesting that th e variation in soil condition among the sites is small in this area. A clear difference in spectral ratio was observed between the observati on points in the heavily damaged area and other areas. The amplificati on of spectral ratio within the frequency range 2-3 Hz, which possibly affected the wooden houses in the area, showed drastic change around the Hankyu Kobe line, with large values between SH3 and SME. This tren d of variation in spectral ratio might be similar to the damage distri bution of wooden houses. The above observation indicates that the site might have a relation to the damage distribution of wooden houses, ev en though aftershocks are a low strain level phenomena.