Masashi TAKAHASHI

Comparison with ground damage investigation in Mid Niigata Earthquake and the earthquake damage of the past

Satoru OHTSUKA

In 2004 Mid Niigata Earthquake, severe damages on natural and artificial slopes generated. It is found the same damages were observed in the former earthquakes as 1847 Zenkoji Earthquake and 1978 Miyagiken-oki Earthquake. It is therefore very important to make good use of the obtained lessons from disasters in disaster prevention measures. In this study, comparative survey on disasters with 2004 Mid Niigata Earthquake was conducted especially on damages of both natural slope and residential area.
It is seen from the survey that not only features of topography and geology, but also forms of disasters are very similar between 2004 Mid Niigata Earthquake and 1847 Zenkoji Earthquake. Both areas are made of soft rock and areas of landslides. Due to active folding stratum, great landslides took place at dip slopes and surface landslides generated at reverse dip slopes. River blockages occurred in both earthquakes at great landslides and it becomes a big subject of disaster prevention measure. Both areas are famous of rice farm shelves constructed on landslide spots and scenic places. The resident has lived with disasters and we have to learn from lessons from the past measures in both areas.
Damage of residential areas was more severe and its recovery was difficult in comparison with public structures. It was found the damage was prominent at border between cutting and filling in both 2004 Mid Niigata Earthquake and 1978 Miyagiken-oki Earthquake. It is apparent that the damage is greater when the base ground is declined and embankment at water catchment landform needs proper drainage measures to reduce disasters.