Fig. 18

\(ka-kL\) diagram (Aki and Richards 1980) for a classification of wave propagation, where k is the wavenumber, a is the scale of heterogeneities, and L is the propagation distance. Red lines show propagation distances from 10 to 150 km, and blue lines show those from 150 to 2000 km. The mean free path at 0.03 Hz is 5000 km, that at 0.1 is 500 km, and that at 0.2 Hz is 30 km