Abstract
The Tertiary mudstone landslide slope around Ohoike pond in Itakura Town, Niigata Prefecture is complicated geologic structure characterized by the prevalence of faults and small landslides.
The strata of slope may be divided into fresh mudstone, weakly weathered mudstone, moderately weathered mudstone, strongly weathered mudstone and colluvial deposit from color and texture of boring core and N values. The groundwater vein-streams run off throuth colluvial deposit, strongly weatherd mudstone and moderately weathered mudstone.
The underground temperature survey reveals three groundwater vein-streams; the West groundwater veinstream, the Center groundwater vein-stream and the East groundwater vein-stream. The gamma-ray spectrometry reveals the NNE direction fault system and NE direction faults system.The NNE direction fault system consist of the West fault, the Central fault and the East fault.The points of radon concentration anomalie of soil-gas coincide with back-scar, side-scar and cracks of foot part of small landslide configurations. From the relationships of the distribution of groundwater vein-steams, fault and fissure zone of combination of the back-scar and side-scar of small landslides, it may be inferred as follows;
(1) The West groundwater vein-stream runs off through the passage of crack caused by the West fault.
(2) The Center and the East groundwater vein-streams run off through the passages of fissure zones.
