Abstract
The Nishikawa landslide in Kôchi prefecture is one of representive landslides occured in the Mikabu green rocks. In order to investigata the mechanism of this landslide, geophysical investigations have been carried out. In this paper, the results of seismic prospecting are discussed.
The relation between rock facies and P wave velosities measured is as follows:
1st layer: 0.3km/s, 5m thick, soil
2nd layer (1): 1.0-1.5km/s, 20m thick, soft, clastic sediment and talus deposit
2nd layer (2): 2.2km/s, 15m thick, soft clastic sediment and weathering part of basement rock
3rd layer: 2.7-3.2km/s, 50m thick, weathering part of basement rock (black schist of Sambagawa southern marginal belt (2.7km/s) and phillitic green rock of the Mikabu green rocks (3.2km/s))
4th layer: 4.0km/s, basement rock
The landslide in this area is closely connented with the weathering Mikabu green rocks, because the head of the landslide exists in the Mikabu green rocks and the sliding part occures in the clastic sediments consisting mainly of the weathering Mikabu green rocks. We must give attention to that it is quite within the bounds of possibillity that the 3rd layer flows plastically for a long time giving a great infuluence on the 1st and 2nd layers and as its result this landslide has occured.
