Non-destructive evaluation of deterioration of the rock-cliff Buddha sculptures (Magaibutsus) in Oita Prefecture, Japan, based on magnetic susceptibility and moisture content

摘要

Deterioration of the rock-cliff Buddha sculptures (Magaibutsus) in Oita Prefecture, Japan, was evaluated by using portable magnetic susceptibility meter and moisture meter. Investigation was carried out for the Magaibutsus of Sugao, Ogata Miyasako, Inukai, Usuki, Monzen and Oita Motomachi. These Magaibutsus were carved in the rock-cliff of the Aso-4 pyroclastic flow sediments.There is a tendency that magnetic susceptibility is high (more than 7 X 10~(-3)SI unit) for the non-deteriorated Magaibutsus preserving pigments on the surface, and moisture content for those Magaibutsus is low (less than 3 percent). On the other hand, deteriorated Magaibutsus have low magnetic susceptibility and high moisture content. The results suggest that the deterioration proceeds in the following order: Ogata Miyasako, Sugao