Figure 6. Spectral amplitudes of records for the events with 2.5 M_L 3 (gray circle) versus hypocentral distance, at the frequencies 2, 5, and 10 Hz. The left frames are for P waves, the right ones for S waves. The solid curves are logA(f, r) obtained from inversion performed at the corresponding frequency. An arbitrary offset has been added to the spectral-amplitude data to make the comparison easier.