Waveform Retrieval and Phase Identification for Seismic Data from the CASS Experiment
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ure and Applied Geophysics
Waveform Retrieval and Phase Identification for Seismic Data from the CASS Experiment ZHIWEI LI,1 QINGYU YOU,2 SIDAO NI,1 TIANYAO HAO,2 HONGTI WANG,3 and CANTAO ZHUANG3 Abstract—The little destruction to the deployment site and high repeatability of the Controlled Accurate Seismic Source (CASS) shows its potential for investigating seismic wave velocities in the Earth’s crust. However, the difficulty in retrieving impulsive seismic waveforms from the CASS data and identifying the seismic phases substantially prevents its wide applications. For example, identification of the seismic phases and accurate measurement of travel times are essential for resolving the spatial distribution of seismic velocities in the crust. Until now, it still remains a challenging task to estimate the accurate travel times of different seismic phases from the CASS data which features extended wave trains, unlike processing of the waveforms from impulsive events such as earthquakes or explosive sources. In this study, we introduce a time-frequency analysis method to process the CASS data, and try to retrieve the seismic waveforms and identify the major seismic phases traveling through the crust. We adopt the Wigner-Ville Distribution (WVD) approach which has been used in signal detection and parameter estimation for linear frequency modulation (LFM) signals, and proves to feature the best time-frequency convergence capability. The Wigner-Hough transform (WHT) is applied to retrieve the impulsive waveforms from multi-component LFM signals, which comprise seismic phases with different arrival times. We processed the seismic data of the 40-ton CASS in the field experiment around the Xinfengjiang reservoir with the WVD and WHT methods. The results demonstrate that these methods are effective in waveform retrieval and phase identification, especially for high frequency seismic phases such as PmP and SmS with strong amplitudes in large epicenter distance of 80–120 km. Further studies are still needed to improve the accuracy on travel time estimation, so as to further promote applicability of the CASS for and imaging the seismic velocity structure. Key words: Controlled source, Wigner-Ville distribution, Wigner-Hough transform, seismic waveform, seismic phases.
1 State Key Laboratory of Geodesy and Earth’s Dynamics, Institute of Geodesy and Geophysics, Chinese Academy of Sciences, Wuhan 430077, China. E-mail: [email protected]; [email protected] 2 Key Laboratory of Petroleum Resource Research, Institute of Geology and Geophysics Chinese Academy of Sciences, Beijing 100029, China. E-mail: [email protected] 3 Institute of Earthquake Science, China Earthquake Administration, Beijing 100036, China.
1. Introduction The active seismic techniques, such as deep seismic sounding, provide high resolution measurements of the crustal velocity structure. Fruitful results on the seismic velocity structure of the crust have been achieved by classic active seismic techniques with explosion source, which is very important to in
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