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Very low frequency earthquakes near the western region of the Ryukyu subduction zone

Very low frequency earthquakes near the western region of the Ryukyu subduction zone. Masataka Ando, Yoko Tu and Cheng-Horng Lin Institute of Earth Sciences, Academia Sinica Yoshiko Yamanaka School of Environmental Sci., Nagoya Univ. Acknowledgement Prof. Kosuke Heki, Hokkaido Univ.

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Very low frequency earthquakes near the western region of the Ryukyu subduction zone

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  1. Very low frequency earthquakes near the western region of the Ryukyu subduction zone Masataka Ando, Yoko Tu and Cheng-Horng Lin Institute of Earth Sciences, Academia Sinica Yoshiko Yamanaka School of Environmental Sci., Nagoya Univ.

  2. Acknowledgement Prof. Kosuke Heki, Hokkaido Univ. for the slow slip data Dr. Hiroyuki Kumagai, NIED for the inversion program

  3. Why focused on Ishigaki-Yonaguni region? Purpose: Comparison of VLFE activity and biannual slow slips at depth (Heki and Kataoka, 2009) Advantages: Numerous large events (M>3.0) having simple waveforms recorded at nearby stations, YNG and ISG

  4. Biannual episodic slips beneath Ishigaki (Heki and Kataoka, 2009)

  5. Hirose et al. Science (2010)

  6. How to select VLFEs? • All seismograms in 2004-2010 were filtered through the bandpass of 0.02-0.05Hz . • Events listed on PDE, JMA, and CWB (Taiwan) catalogs were deleted. • Events recorded by stations <5 were deleted (M<2.0).

  7. An example of swarm-type VLFEs south of Ishigaki and Yonaguni Passband: 0.02-0.05 Hz 200s YNG 2500km IMG 30 min

  8. VLFEs recorded at ISG(Ishigaki), Dis= 50km Passband: 0.02-0.05 Hz E W 600s N S U D

  9. An example of Isolated VLF earthquake, Mw4.0 2010/01/10 01-03 Passband: 0.02-0.05 Hz YNG IMG 3 hours

  10. 01:h20m20s, JAN 2009 , Mw4.0 60s E W N S U D 01h 20m 50s

  11. 01:h20m20s, 10 JAN 2010 Mw4.0

  12. b-value of VLF events in the YNG and IGK region in 2007 1000 N=263 Log n=a-1.9Mw 100 Cumulative number 10 1 Magnitude

  13. Daily number of VLFE, 2004-2010 In the Ishigaki-Yonaguni region 2010 2008 2009 2007 2006 2005 2004

  14. Daily number of VLFE, 2004-2010 30-day running mean 2009 2010 2006 2007 2008 2004 2005

  15. Power spectral analysis of daily number of VLEF Daily number of VLEF 2004-2010 4.9 months 11.4 months 13.7

  16. Daily number of VLFE, 30-day running average v.s. Slow slips (Heki, 2011)

  17. Monthly number Interval, month This study Heki & Kataoka (2009)

  18. Summary • VLFEs in the Ishigaki-Yonaguni area between 2004 and 2010 have been analyzed. • Dominant intervals of VLFE activity are 5 and 12 months. • The VLFE activity is possibly related to the slow slip activity at depth. • Furthermore, the correlation between the VLFEs activity and the seismic moment should be analyzed.

  19. Supplemental

  20. Heki and Kataoka (2009)

  21. 2004-2010 30-day running average

  22. 2004-2010 30-day running average

  23. 2004-2010 30-day running average

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