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Yoko Tu 1 , Kosuke Heki 1 , Masataka Ando 2 and Hiroyuki Kumagai 3

＊. The connections and variations between recurrent slow slip events and very low frequency earthquakes near the southwestern Ryukyu subduction zone. Yoko Tu 1 , Kosuke Heki 1 , Masataka Ando 2 and Hiroyuki Kumagai 3

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Yoko Tu 1 , Kosuke Heki 1 , Masataka Ando 2 and Hiroyuki Kumagai 3

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  1. ＊ The connections and variations between recurrent slow slip events and very low frequency earthquakes near the southwestern Ryukyu subduction zone Yoko Tu1, Kosuke Heki1, Masataka Ando2 and Hiroyuki Kumagai3 1.Department of Natural Historical Sciences, Hokkaido University, Sapporo, Japan 2.Center for Integrated Science and Education of Natural Hazard, Shizuoka University, Shizuoka, Japan 3.Department of Earth and Planetary Sciences, Nagoya University, Nagoya, Japan

  2. The Ryukyu subduction zone is decoupled ＊ No largethrust earthquake ＊ GPS velocity vectors show a trenchward motion. Marianatype ＊ Back-arc spreading system.

  3. The Ryukyu subduction zone is coupled ＊ SSEs(Heki & Kataoka, 2008; Nakamura,2009) Kyushu ＊ VLFEs(Ando et al., 2012) ＊ Seafloor geodetic surveys (Nakamura , 2010 ; Ando et al., 2014) Okinawa Ishigaki Island Ryukyu subduction zone Taiwan ＊ Tsunamideposits on Ishigaki Island (Ando et al., 2014)

  4. The mode of Ryukyu subductionzone Okinawa islands The Ryukyu subduction zone Sea level Ryukyu trench VLFEs Slow slips Lock ? Philippine Sea plate The Nankai trough Obara et. al ( 2005)

  5. What are SSEs and VLFEs ? ＊ Slow Earthquakes(Beroza and Ide, 2011) ＊ Low frequency VLFEs0.1~0.01HZ seismometers SSEs Day, Week, Month or Year global position system(GPS) ＊ Occur on subduction zones and relate to large thrust earthquakes.

  6. Where do SSEs and VLFEs occur in Japan? SSEs VLFEs Ikeda & Heki, 2014 Obara et al.2004 Japan trench Japan trench Ozawa et. al, 2003,2007 Hirose et. al,2010 Nankaitrough Obara,2010,2011 Nishimura et. al,2013 Nankaitrough Obara & Ito, 2005 Yamanaka, 2008

  7. Where do SSEs and VLFEs occur in Okinawa? SSEs VLFEs Nishimura, 2014 Ando et al., 2012 Nakamura., 2014:Asano, 2014 Heki & Kataoka, 2008 Nakamura, 2009 Ryukyu trench Ryukyu trench

  8. Pre-researches of SSEs and VLFEs SSEs VLFEs Ando et al., 2012 Heki and Kataoka, 2008 ＊ GEONET GPS datain 1997 ~2007 21 SSEs Recurrence Interval is 6 months 20-40 km depths ＊ ＊ ＊ F-net datain 2007 More than 2000 VLFEs All shallow thrust earthquakes 10-30 km depths ＊ ＊ ＊ ＊

  9. Methods of SSEs GEONETGPS 1997-2014 SSEs Daily displacements Okinawa Trough Irabu Find SSEs by vision Delete earthquakes and antenna change Yonaguni Miyako Tarama Ishigaki SSEs Iriomote Hateruma Coseismic dislocation model (Okada, 1992) Ryukyu trench Magnitude Fault patch

  10. Amount and recurrent interval of SSEs Haterumaw.r.tMiyako SSE#1 20 10 32 2 30 N20W (mm) 32events 1998/03M7.5 2001/12M6.7 2002/03M6.4 2013/04M6.1 Up (mm) 7.00 m Average interval 6.37m 6.24 m Interval (months) Number 4.5 m SSE#number Interval (months)

  11. Can we find any seasonalityof SSEs? Heki and Kataoka, (2008) 1997-2007 1997-2014 Numberof events JFMAMJJASOND Occurrence ＊ ＊ Spring /Autumn Summer /Autumn

  12. Fault patch detection EX : SSE#17 Coseismic dislocation model DC3D/DC3D0 by OKADA, 1992 94km Strike: 250° 66km Dip: 15° NNE Depth: 32km Center : 123.78 , 24.45

  13. Fault patches of 32 SSEs 6.6 (Mw)

  14. Correction between recurrence interval and fault slips Heki and Kataoka, (2008) ＊

  15. Cumulative slip by SSEs 1997 to 2014 Eq#1 Eq#2 Eq#3/4 6.6cm/yr 30 10.51cm/yr 20 8.67cm/yr Cumulative slip (m) 9.53cm/yr the polynomial of degree 5 10 Eq#5 SSE#1 Time (yr)

  16. Methods of VLFEs BATS F-net VLFEs Data Base Band-pass Filter, 20-50s Delete Catalogued Earthquakes (PDE, JAM and CWB) VLFE Inversion Technique (Nakano et al. ,2008) CMTSolution Location

  17. One example of VLFEs 2007-06-11 RAWdata Bp 20-50s

  18. The location and focal mechanisms of VLFEs

  19. Number of VLFEs in 2007 to 2009 ＊ 936 events Yunagoni Ishigaki Miyago

  20. The time series of VLFEs in 2007 to 2009 Daily data Monthly data

  21. The connection of occurrence time SSEc Monthly VLFEs Daily VLFEs

  22. The connection between the slip value variations of SSEs and the number of VLFEs 6.6cm/yr Eq#1 Eq#2 Eq#3/4 10.51cm/yr 30 20 9.53cm/yr 8.67cm/yr Cumulative slip (m) 374 319 10 243 Eq#5 SSE#1 Time (yr)

  23. The connection between the slip value variations of SSEs and seismic data---Ryukyu trench 1997-2014 6.6cm/yr Cumulative slip (m) Eq#1 Eq#2 Eq#3/4 10.51cm/yr 30 9.53cm/yr 20 8.67cm/yr Mw 10 Eq#5 SSE#1 Number

  24. The connection between the slip value variations of SSEs and seismic data---Okinawa trough 1997-2014 6.6cm/yr Cumulative slip (m) Eq#1 Eq#2 Eq#3/4 10.51cm/yr 30 9.53cm/yr 20 8.67cm/yr Mw 10 Eq#5 SSE#1 Number

  25. Conclusions ＊ 32SSEs and 936 VLFEs were detectedfrom GEONET GPS data and F-net board band seismicdata near Ishigaki Island, southwest Japan. ＊ Thoseevents occur along the Ryukyu subduction zone. The depths of SSEs are between 20-40km and the depths of VLFEs are between 10-30km. ＊ The average recurrence interval of SSEs is 6.3 months. However, the interval period suddenly decreases to 4.5months during 2005 to 2007and then back to the previous level. ＊ The slip volume ofSSEs in this area was not aconstant. From 1997 to 2008, slip volume is about 10cm/year, but the volume became 6cm/year only in 2008 to 2014.

  26. ＊ Taking into the results of slip amount variations of SSEs and the amount of VLFEs, we find that SSEs and VLFEs activities have a negative correlation in this area. ＊ Moreover, magma injection which occurred in Okinawa trough could relate to the activity of SSEs.

  27. Thank you for your attention ＊

  28. YNG&IGK ZMM&KGM AMM KYK&TAS M7.9shichuanearthquake

  29. TAS 2007-2008 KYK AMM KGM ZMM IGK YNG TDCB NACB YULB TWGB

  30. 2007-2008 TAS KYK AMM KGM ZMM IGK YNG TDCB NACB YULB TWGB

  31. B A B̕ A̕

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