In the first half of this paper, possibility of damage to houses and housing sites in the event of a similar earthquake to the 1978 Off-Miyagi Earthquake is discussed based on the investigation of long term variation in N values in the ground below severely damaged houses. Thus, we performed bore tests and Japanese standard penetration tests at 18 locations in the five housing districts in 1978, 1985 to Ô86, and 1996 to Ô97. In addition, the effectiveness of preventative repair works in the twenty years following the earthquake is investigated. In the second half of this paper, an empirical method for predicting liquefaction-induced damage to houses was proposed. This method is derived from the relationship between the thickness of the non-liquefied layer (H1) and that of the liquefied layer (H2), which were obtained from the result of the surveys: bore tests, Japanese standard penetration tests, grain size analysis and interviews with residents. In addition, it is reported what kind of foundations, which had been executed before the earthquake, remained intact during the 1983 Nihonkai-Chubu Earthquake. Thus, an empirical method reducing liquefaction-induced damage to house is proposed.
(1) Midorigaoka housing district Figure.1 is an aerial view of extremely damaged housing sites in Midorigaoka 1-chome. Eleven houses in block A and seven houses in block B, as shown by hatching in Figure.1 were so severely damaged by the earthquake that these owners were obliged to move. During the six months following the earthquake, the slope has been moving in the direction of A-AÕ, and at the depth of 18.5m where in the sandstone bedrock, a sliding plane was observed.