11:15 〜 11:30
[SSS27-08] 減衰媒体におけるスウィープ波形の伝播過程とその利用
キーワード：地震波減衰, 速度分散, スウィープ波形
The sweep signal is the most extensively used land seismic exploration technique. In conventional data processing using sweep signals, a received trace is cross-correlated with source sweep to convert the extended sweep signal into a pulse signal. For attenuation estimation, a time window is often used to compute the frequencies of the direct-arrival waveforms. Uncorrelated sweep signals are useful in the discussion of harmonics simply because the uncorrelated data are one of the few situations in which we commonly input a nearly pure frequency into the earth. Our previous study proposed a method that enables accurate measurement of ultrasonic attenuation using sweep signals under the assumptions that velocity dispersion can be ignored and the quality factor (Q) is not dependent on frequency. This method is independent of the effect of windowing while the windowing effect underestimates the attenuation results due to a spectral leakage effect. In most cases, however, the presence of attenuation is accompanied by velocity dispersion because of causality. The presence of velocity dispersion causes attenuation to be disturbed, although the proposed method is not so sensitive to the presence of velocity dispersion. The present paper elucidates the wave propagation process of sweep signals in attenuative media with velocity dispersion to develop the method which can take the effect of dispersion into account. We obtain a time-scale representation of sweep signals by using the continuous wavelet transform method to perform a time-series analysis of a seismic trace that decomposes the trace into its respective amplitude and phase components in both the frequency and time domains.