Body-wave spectral structure of 14 earthquakes with m_b? 6.0 determined from long-period records of WWSSN stations for 1964?74

Abstract

The far-field displacement amplitude spectra of 14 earthquakes from Iran, Fiji Islands, Tonga-Kermadec Islands, and South America were obtained using the long-period P and S-wave records of the WWSSN stations.Despite recent improvements in theories of the seismic-source mechanism there is continuing doubt concerning the interpretation of the observed seismic spectrum. Although the dislocation model has been adopted by many investigators, and in particular Brune's model is widely used, there has often not been satisfactory evidence in the observed spectral data to justify this. Generally speaking, however, the spectral structures obtained in the present work have a form closely similar to those calculated by Brune and Savage, and it is shown that anomalies in the observed amplitude spectral structure are most likely due to noise and propagation effects.In order to show the effect of noise in the amplitude spectra an average noise spectrum was obtained from several noise samples taken immediately before the arrival of P waves (Fig. 5). The spectra were corrected in the same way as the earthquake records. Fig. 5 shows that the 9 Body-wave spectral stmcture of earthquakes 23 7