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| | Abstract | | Damage of wooden houses was observed in Iizuma in the Nagano prefecture during the 2007 Niigataken Chuetsu-oki earthquake, although the town is about 90km away from the epicenter. The seismic intensity and peak ground acceleration at a strong motion station in the damaged area of the town are 6-upper in the JMA scale and 620 cm/s/s, while those at a site without any damaged wooden houses in the town are 5-upper and 280 cm/s/s. Since the two stations are only 4km apart from each other, it is suggested that site amplification is one of the possible reasons for the differences of the ground motions. We investigated the reasons why the seismic intensity in the town is so high from filed surveys. First, we conducted aftershock observation at 11 sites in the town to understand spatial distribution of earthquake ground motion. Then, geophysical explorations were conducted in the area to known S-wave velocity profiles. Next we investigated effects of shallow soils on earthquake ground motion in the area using the results of the earthquake observation and the geophysical explorations. |
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