下総震動地塊について  [in Japanese] Strong motion of the Shimofusa seismic quaked massif  [in Japanese]

A major earthquake hited the south of Kanto district causing widespread damage to houses on the afternoon of Thursday, the 17th of December, 1987. The quake, which was centered about 10 km east off the Kujukuri coast, registered magnitude 6.7 on the JMC scale. Near epicenter, sand with underground water boiled out and cliffs breaked down. Chiba prefecture suffered most of this strong earthquake. The remarkable earthquake-stricken district is bordered on the north by the river Tone alluvial plain, on the west by the lake Inba low ground and on the south by the Mineoka hill. Numerous houses were wrecked by the violent motion in the above mentioned area. A great deal of damage was done to the roofing tile, especiallly ridge tile. An analysis of this injury pattern shows that many of breakage of roofing tile can be explained as a result of distortion of houses causing by the strong motion of the quake. Elsewhere in the soft ground area, it is thought that wooden house is easy to break. But the soft sediments such as an artificial ground and Holocene sediments are restricted in distribution in the studied area. Accordingly, it can not be considered that the greatspehere damage is caused only by the soft ground. Widespread strong initial motion seems to be influenced by the deep-seated fault block. The writer named this fault block by the Shimofusa seismic quaked massif.