2. Seismic coupling, down-dip limit of the seismogenic zone, and dehydration of the slab Tetsuzo Seno （ Earthquake Res Inst, Univ of Tokyo ）

3. Along-arc variation of Seismic coupling & Down-dip limit of the seismogenic zone near Japan in relation to Dehydration from the subducted crust (Low-frequency tremor)

4. Seismic coupling along the Nankai - Sagami Troughs Eurasian plate Okhotsk plate Pacific plate Philippine Sea plate Seno et al. (1996) Seno et al. (1993)

5. Yagi (2002) Occurrence of smaller earthquakes in Hyuganada

6. 1703 Genroku 1923 Taisho Tokai, 1707, 1854 ~150 yrs ~400 ~1500 ∞ ∞ Central Honshu Recurrence intervals of great earthquakes Izu Kanto

7. Nankai Trough ~50% Sagami Trough ・ Vc = 3 cm/yr ・ U = 6 m ~100 % ・ Vc = 4 - 6 cm/yr ・ U = 4 - 6 m Seismic coupling coefficient ・ T = 90 - 150 yrs ・ T = ~400 yrs Taisho Kanto (Seismic slip/plate motion)

8. Oleskevich et al. (1999) Down-dip limit of the seismogenic zone

9. Seno & Pongsawat (1982), Seno et al. (1980) 1978 Miyagi-oki earthquake (M7.5) 50 km Miyagi-oki, n. Honshu

10. Kawakatsu & Seno (1983) Northern Honshu: three types of events Thrust Down-dip compression Down-dip tension

11. Kawakatsu & Seno (1983) Whole section: three types of events Thrust Down-dip compression Down-dip tension

13. Hori (1997) Philippine Sea slab beneath Kanto

14. ● ● ● ● ● ● thrust Goto (2001) S. Kyushu P-axes ●

15. Seismic coupling Down-dip limit of the seismogenic zone in relation to Dehydration from the subducted crust (Low-frequency tremor) Basic assumptions

16. 100 MPa1 GPA 3 km 30 km Lithostatic pressure Depth Tectonic stress Weakening Fault strength

17. Interplate earthquakes Elevated pore fluid pressure Slab earthquakes (intermediate-depth) Dehydration instability Weakening mechanisms

18. Dehydration instability: Serpentinite Raleigh & Paterson (1965)

19. (a) Cold slab type (b) Hot slab type Dehydration from crust Dehydration from crust Dehydration from serpentine Dehydration from serpentine Dehydration loci for slab seismicity Yamasaki & Seno (2003)

20. Obara (2002) Low-frequency Tremor in the upper plate wedge

21. Low freq. tremor Freq. great earthquakes Subduction of Normal oceanic crust Island-arc crust subduction No dehydration Dehydration from crust No low freq. tremor No great earthquakes No dehydration Hot slab type: Nankai Trough N. of Izu Crust Upper plate

22. Tokai district: easternmost Nankai Trough Seismicity: Matsumura (1997) 350°C Low frequency tremor (Obara, 2002) Dehydration From crust Piosson’s ratio (Kamiya & Kobayashi, in prep.) Temperature: Seno & Yamasaki, in prep.

23. Obara(2002) 震源 Low-frequency earthquakes & tremor: Upper plate

24. Okino et al. (1999) Low-frequency tremor ~ Moho depth (Obara, 2002) Kanto E. Shikoku S.Kyushu No tremor region

25. Okino et al. (1994) Kinan seamount chain

26. Subducted continental or island-arc crust is mainly composed of granite, then does not involve dehydration. No low-frequency tremor No earthquake within the subducted crust Hypothesis:

27. Later crustal phase Serpentine dehydration loci Serpenine dehydration loci a) Event in the oceanic crust b) Event in the mantle Generally along the Nankai Trough Discrimination of crustal events No later crustal phase

28. Hori (1997) PHS slab beneath Kanto (no tremor) No later phase (Hori, 1990)

29. Kurashimo et al. (2002) E. Shikoku (no tremor)

30. Hayashimoto et al. (2001) a a 110 km 200 km DDC DDT DDT, i.e., lower plane seismicity in the mantle S. Kyushu (no tremor)

31. Goto et al. (2001) DDTThrust mantle thrust S. Kyushu

32. Areas without earthquakes within the subducted crust Kanto E. Shikoku S. Kyushu （？） Areas without low-frequency tremor

33. Noguchi & Sekiguchi (2001)Obara (2002) High Vp Top of slab seismicity Izu Kanto Slab

34. Ni & Barazangi (1986) Mature collision zones: Zagros and Himalaya

35. Low freq. tremor Freq. great earthquakes Normal oceanic crust subductionIsland-arc crust or continental crust subduction No dehydration Dehydration from crust No low freq. tremor No great earthquakes No dehydration NankaiTroughN. of Izu, Zagros, Himalaya Crust Upper plate

36. Areas with island-arc or continental crust subducted Kanto, E. Shikoku, S. Kyushu Infrequent large interplate earthquakes vs. N. Izu, Zagros, Himalaya No or very rare large interplate earthquakes

37. Hori (1997) Philippine Sea slab beneath Kanto

38. Shikoku Basin Izu-Bonin Arc Trench Axis Serpentine stable V. F. Origin of the double seismic zone in Kanto Seno et al. (2001); Seno & Yamasaki, in prep.

39. No dehydration from crust No low freq. tremor Infreq. great earthquakes & deep thrusts Kanto Dehydration from serpentine

40. Kawakatsu & Seno (1983) Northern Honshu: three types of events Thrust Down-dip compression Down-dip tension

41. Kawakatsu & Seno (1983) 1994 aftershocks (Hino et al., 2000) Yamanaka et al. (2001)) Epicenter Asperity Larger events

42. (a) (b) Vp in northen part of n. Honshu S. Ito et al. (2000) Depth = 40 km WE

43. No serpentine Fractured zone Dehydration Ductile shear zone + hydrofracturing Repeated earthquakes Plastic flow Dehydration Cold mantle wedge N. Honshu, Kanto, S. Kyushu Iwate-oki, Bonin, Tonga Serpentine 350°C Anisotropic permeability

44. Plastic flow Dehydration Hot mantle wedge Nankai, Ryukyu, Cascadia, Mexico Ductile shear zone + hydrofracturing Serpentine 350°C

45. No serpentine Stable sliding with very high shear stress No dehydration Collision zone N. Izu, Himalaya, Zagros No serpentine No dehydration or delamination

46. Conclusions ・ Sudbduction of island-arc or continental crust does not involve dehydration of subducted crust, then does not induce low- frequency tremor in the wedge, or large interplate earthquake. ・ If sudbduction of island-arc crust accompanies dehydration of the serpentinized mantle, it produces large interplate earthquakes infrequently. ・ Thrust zone in the manle part may evolve into either of the two branches: earthquake-no serpentinized wedge or no earthquake-serpentinized wedge. This determines the down-dip limit of the seismogenic zone. ・ Earthquake occurrence in Kanto may be a result of no earthquake occurrence in Bonin; if Bonin generated great earthquakes, Kanto would have turned into a mountain belt.