The evolution of source characteristics of acoustic emission (AE) events and the surface topography of the fault surface during frictional sliding were investigated with the aim of improving current understanding of the microscopic process of friction. Both the AE source dimensions and the grain-scale topographies were well conserved against abrasion during the sliding, but the magnitude of stress drop was significantly reduced. The fractal-domain topographies, the wavelength of which is

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... than the fractal limit wavelength (λ c ), were significantly worn during the sliding. These results suggest that the grain-scale topography determined the AE source dimension, while the fractal-domain asperities controlled the magnitude of the stress drop. Since elastic wave radiation is one of the major energy consumption processes, the grain-scale and the fractal-domain topographies may play different roles, not only in the AE source process but also in the friction of rocks.