The source region of the Earthquake off the Coast of Izu peninsula was at the southern tip of Izu Peninsula. Seismic intensity 5 in JMA scale was observed at Irozaki in Minamiizu (Fig.6-30). There were a total of 30 fatalities and 134 houses completely collapsed in this area. Damage also occurred to roads, bridges, and water pipes (Fig.6-31). This damage was particularly severe in the Nakagi region of Minamiizu, where landslide occurred, engulfing an inhabited area and killing 27. Tide stations in Omaezaki and Minamiizu observed a small tsunami of less than 20 cm. In conjunction with this earthquake, fault offset was visible at the earth's surface for a length of about 5.5 km in a northwest direction from the vicinity of Irozaki (Irozaki fault, Fig.6-32). The maximum offset was 45 cm in the vertical direction, with upheaval on the southwest side, and 25 cm in the lateral direction.

As shown in Fig.6-33, the number of perceptible and imperceptible aftershocks decayed. The largest aftershocks (M 4.5) occurred about one hour after the main shock (Fig.6-34).

Various phenomenon occurred frequently on Izu Peninsula and the surrounding area after the earthquake, including M 6-7 earthquakes, swarm activity, and crustal deformation of upheavals. A volcano erupted on the sea floor off the coast of Ito City in July 1989.

The source region of the Earthquake Near the Coast of Izu Oshima Island extended from western Izu Oshima Island to central Izu Peninsula. Seismic intensity 5 in JMA scale was observed in Izu Oshima and Yokohama (Fig.6-35). There was extensive damage in central and southern Izu Peninsula, with 25 fatalities, 96 houses completely collapsed, and damage to railroads and roads. In addition, some houses on Izu Oshima Island were partially collapsed (Fig.6-36). Much of this damage was caused by the landslides and falling rock (Fig.6-37). In addition, the embankment at the site for piling slag at the Mochikoshi Mine in Yugashima was destroyed, causing further destruction when muddy flows that contained noxious material entered the Kanogawa River. The largest aftershock (M 5.8) occurred the following day, causing damage in the western Izu Peninsula. The main shock generated a small tsunami. Tide stations recorded its height at 70 cm in Izu Oshima Okada, 14 cm at Minamiizu, and 22 cm at Mera in Chiba Prefecture.

Foreshock activity occurred on the previous day. There were dozens of earthquakes, the largest of which was M 3.7, on the western side of Izu Oshima. These lasted from after 5 p.m. on January 13 to late at night. The activity began again after 8 a.m. on the 14th, and included many earthquakes, two of which were M 4.9 events. The Japan Meteorological Agency issued earthquake information at 10:50 a.m. that day, stating that an earthquake with the potential to cause damage could occur. The main shock occurred about 90 minutes later. As shown in Fig.6-38, the number of perceptible aftershocks decreased, with the largest aftershock (M 5.8) occurring on January 15 (Fig.6-39).

The eastern half of the earthquake's source region was at sea, so it is not known whether offset caused by faulting occurred on the sea floor. Slip caused by faulting was confirmed on Izu Peninsula.

The descriptions of damage for this earthquake show that extensive damage frequently occurs in the Izu Peninsula area due to the landslide caused by seismic ground motion.