(6)The Earthquake off the East Coast of Chiba Prefecture (December 17, 1987, M 6.7)


This earthquake occurred at a somewhat deeper location of about 50 km near Kujukurihama Beach on the Boso Peninsula. It occurred within the subducted Philippine Sea Plate, causing fault movement along a plane that split the plate vertically. Seismic intensity 5 in JMA scale were observed in Chiba, Choshi, and Katsuura Cities. Two fatalities occurred in Chiba Prefecture (Fig.5-27); no tsunami was observed with this earthquake.

This earthquake attracted a great deal of public attention because it was the first since the Kanto earthquake of 1923 to have caused extensive damage over a wide area in Tokyo. There were many instances in which roof tiles on wooden houses broke and fell off, sharply sloping land collapsed, and block walls collapsed. A large amount of damage from liquefaction was observed in areas with relatively soft ground, including the Tokyo Bay coast, the Kujukuri Plain, and the Tonegawa lowlands (Fig.5-28 and Fig.5-29, Fig.5-30).

The largest aftershock M 5.2 occurred about one month after the main shock (Fig.5-31).