Abstract
The destruction by the Tokachi-oki Earthquake in Towada City on the Sambongi-hara fan, eastern Aomori Prefecture, was concentrated at the northeastern quarter of the built up area. Here, the main irrigation canal on the fan had acted as a supply origin of ground water, because of the lack of water-proof lining 800m long.
The heavy rain of 3 days before the earthquake added the supply of ground water, and the building grounds were soaked and getting fragile against any shake.
The fact that the distribution of severe damage coincides with the flow direction of ground water tells us the influence of ground water in bringing the earthquake damages.
The destruction in Misawa City to the east of Towada City was concentrated at the reclaimed land of Furumagi area, where houses were crowded on the soft reclaimed ground.
