[S-SS11] Strong Ground Motion and Earthquake Disaster

[SSS11-02] Spectral decomposition by cepstrum from strong motion records in autocorrelation analysis

*Tomotsugu Watanabe¹, Hiroshi Takenaka¹ (1.Okayama University )

Keywords:seismic motion, strong motion, autocorrelation function

We propose a spectral decomposition method by the cepstrum from seismic waveforms to elucidate the real sedimentary structures. Recently, the application of the autocorrelation function from strong motion records has been studied based on seismic interferometry for investigating the interface between the bedrock and sedimentary layers. The trace of the autocorrelation function corresponds to the zero-offset reflection profile in seismic exploration whose signals represent reflected waves from the boundaries with large contrasts in the seismic velocity. We have emphasized that the cepstrum, which is the inversed Fourie transform of the logarithmic power spectrum, is a powerful tool for detecting signals from shallow sedimentary structures with high resolution (Watanabe and Takenaka, 2024, JpGU; SSJ; AOGS).

Strong motion waveforms consist of source, propagation path, and site amplification characteristics. The spectral whitening method is the key to the successful way in the autocorrelation analysis for extracting the information of sedimentary structures in detail. This method is performed by dividing the original power spectrum by its smoothing one, but the smoothing bandwidth for this operation is selected empirically by trial and error. In this study, we assume both source and attenuation effects as the omega-squared model and the exponential function and then subtract these models from the cepstrum instead of the spectral whitening method. In the quefrency domain, spectral decomposition is easily conducted because lower order of the cepstrum mainly includes the source effects and higher has site ones.