The linear relation between logarithms of maximum amplitude and hypocentral distance are known to hold good observationally. But, the direct evaluation of the Q-1 factor from the linear coefficient has been difficult. Here, supposing a random and fractally homogeneous distribution of absorbers or scatterers with fractal dimension Da in a space of dimension d, we can analytically calculate the relation between amplitude and distance. The commonly accepted exponential decay formula corresponds to a special case of Da=d. The amplitude is written as a negative power of distance in the case of Da=d-1: the negative power is directly related to the linear coefficient between logarithms of amplitude and distance. If seismic faults correspond to absorbers or scatterers, the equality Da=d-1 is qualitatively in harmony with the well known fact that the hypocenter distribution of microearthquakes has a fractal dimension being smaller than d. ¿ American Geophysical Union 1988