Journal of Natural Disaster Science

The July 1997 Landslide Disaster at Harubun, Sasebo, Japan

Keinosuke GOTOH and Minoru YAMANAKA
Faculty of Engineering, Nagasaki University,

(Received 24 July, 1998 and in revised form 12 February, 1999)

Abstract

Japan is a country of many geological hazards, including volcanic activity, earthquakes, and landslides. Of these, landslides triggered by heavy rainfall tend to occur during the yearly rainy season from early June through the middle of July. Sasebo City, located in the northwest part of Kyushu Island, is one of the most landslide-prone places in Japan.

Results of a series of investigations done to establish an outline of a landslide and its causes are reported. This information provides some important factors in disaster prevention for the Hokusho-type of landslide. The landslide described here is a typical, secondary sliding Hokusho-type, the result of erosion caused by rainfall on weak strata. It occurred on a gentle, concave hillslope, on which both surface and ground water tend to concentrate.

On the basis of its characteristics, the main causes and mechanism of this landslide are described and some lessons learned discussed. Constructive proposals and countermeasures to be taken to prevent the occurrence of landslides, which are based mainly on an effective drainage system are considered.

Key words

landslide, damage survey, land development, countermeasure works, evacuation