Abstract
Structural feature of the weathered zone developed in granites was analysed by mirage method, and it was clearified that the increasing rate of P-wave velocity at land surface is proportional to the surface velocity there. This fact suggests that weathering is a kind of diffusion process satisfying the diffusion equation with the surface evaporation boundary condition at the land surface, because that the velocity is proportional to the rock density, namely to the mass concentration, approximately. The upper most portion of the weathered zone has been truncated by erosion and this is reflected in the oblique relation of the iso-velocity plane to the land surface. Mutual relationship between the velocity at the surface and the landform parameters, the slope gradient and the equivalent slope length, was obtaind to discuss the stability of slope in connection with the general topographic profile of the survey area.
