Journal cover Journal topic
Natural Hazards and Earth System Sciences An interactive open-access journal of the European Geosciences Union
doi:10.5194/nhessd-3-675-2015
© Author(s) 2015. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
22 Jan 2015
Review status
This discussion paper has been under review for the journal Natural Hazards and Earth System Sciences (NHESS). The manuscript was not accepted for further review after discussion.
Formation time and mean movement velocities of the 7 August Zhouqu debris flows extracted from broadband seismic records
Z. Li1, X. Huang1, Q. Xu2, J. Fan1, D. Yu1, Z. Hao3, and X. Qiao4 1China Earthquake Networks Center, Beijing, 100045, China
2State Key Laboratory of Geohazard Prevention and Geoenvironment Protection, Chengdu University of Technology, Chengdu, 610059, China
3Lanzhou Institute of Seismology, China Earthquake Administration, Lanzhou, 730000, China
4Institute of Seismology, China Earthquake Administration, Wuhan, 430071, China
Abstract. The catastrophic Zhouqu debris flows, which were induced by heavy rainfall, occurred at approximately midnight of 7 August 2010 (Beijing time, UTC + 8) and claimed 1765 lives. Broadband seismic signals recorded by the Zhouqu seismic station nearby are acquired and analyzed in this paper. The seismic signals are divided into two separate parts for the first time using the crucial time of 23:33:10 (Bejing time, UTC +8), with distinctly different frequency characteristics on time-by-time normalized spectrograms and amplitude increasing patterns on smoothed envelopes. They are considered to be generated by the development stage and the maturity stage of the Sanyanyu debris flow respectively. Seismic signals corresponding to the development stage have a broader main frequency band of approximately 0–15 Hz than that of the maturity stage, which is around 1–10 Hz. The N–S component can detect the development stage of the debris flow about 3 min earlier than other components due to its southward flow direction. Two sub-stages within the maturity stage are recognized from best-fitted amplitude increasing velocities and the satellite image of the Sanyanyu flow path and the mean movement velocities of the Sanyanyu debris flow during these two sub-stages are estimated to be 9.2 and 9.7 m s−1 respectively.

Citation: Li, Z., Huang, X., Xu, Q., Fan, J., Yu, D., Hao, Z., and Qiao, X.: Formation time and mean movement velocities of the 7 August Zhouqu debris flows extracted from broadband seismic records, Nat. Hazards Earth Syst. Sci. Discuss., 3, 675-695, doi:10.5194/nhessd-3-675-2015, 2015.
Z. Li et al.
Z. Li et al.

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Short summary
In this manuscript, the actual formation time of the August 7th Zhouqu debris flows is determined to be 23:33:10 using time-by-time normalized spectrograms of broadband seismic records for the first time. Seismic signals corresponding to the maturity stage are further divided into four sub-stages. Combined with the satellite image of the Sanyanyu flow path, the mean movement velocities of the Sanyanyu debris flow during sub-stages 2 and 3 are estimated to be 9.2 m/s and 9.7 m/s respectively.
In this manuscript, the actual formation time of the August 7th Zhouqu debris flows is...
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