Damage caused by the 1989 OFF-IZU Peninsula Earthquakes

Damage caused by the earthquake swarm off-shore of the Izu Peninsula, which started on June 30, particularly by the largest earthquake of July 9 of magnitude 5.5, was investigated. In spite of the large ground accelerations (233 gal) recorded on the basement of Ito City Hall, no severe damage to structures was observed, except that the ridge roof tiles of many houses fell off and tombstones in some cemeteries fell over. More than 90 percent of tombstones fell down in Hosenji temple, which stands on reclaimed ground on a hill side. This damage indicates that the vertical ground motion was particularly large, due to the short epicentral distance. Normal functioning of life line systems, i.e., gas, water, electricity, telephone and railways recovered within several hours of the earthquake. Damage was concentrated in the area around the JR (Japan Railways) Ito station and the Usami district about 2 km west of the epicenter. Each areas is no an alluvial basin surrounded by rocky hills. Because of the heavy rain before the earthquake, the ground contained much water and the retaining walls of reclaimed land broke, resulting in uneven settlement of the ground and subsidence of houses. Although there was relatively light damage to structures, unusual rumbling in the ground due to the movement of magma frightened people, and they witnessed the under-sea eruption on July 13. Also, some citizens fled due to rumors of a possible tsunami. Ito, a famous swimming resort in Japan, suffered large economical damage due to the cancellation of hotel reservations