SPECTRAL ANALYSIS OF SEISMIC WAVES : PART 1. DATA WINDOWS FOR THE ANALYSIS OF TRANSIENT WAVES

Abstract

Causes of strong undulations generally observed in the spectra of seismic initial phases have been theoretically investigated and attributed to the effects of the sharp truncation of signals and of the incidence of later phases. Characteristics of observed amplitude and phase spectra have been shown to coincide well with theoretical considerations. In order to derive the fine structure of the spectra of initial phases, the choice of data windows suitable for the purpose and the selection of an appropriate time interval of analysis to exclude the effects of later phases are indispensable. Further, in the spectral analysis of seismograms, care must be taken over the worsening of spectra caused by the simplification of analytical procedure, namely, the reversion of the order of steps, correction of instrumental response and superposition of data windows, especially when a heavy data window is applied. The behavior of data windows to be superposed on initial phases and that of the corresponding spectral windows have been examined in detail.