In order to detect groundwater distributed nonuniformly over a landslide area, methods utilizing mechanical or electrical properties of soil and water have been applied up to now. However, groundwater by these techniques can be either that having a direct influence on the landslide activity or that having little influence on it, and therefore, prevention works undertaken on the basis of the obtained results have been very often unsatisfactory. The author has come to the view that the utilization of thermal properties of water and soil, to which little attention has been paid so far, will make it possible to detect groundwater-vein stream having a significant influence on the landslide activity, and has pursued theoretically the applicability of exploring the vein by measuring one-meter-depth underground temperature (Takeuci,1980). As a result of the investigation, it revealed that this method is an effective method of determining the location of groundwater in the formed vein stream.

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