Divergent boundary

1. Three types of plate boundaries Divergent boundary Transform fault Convergent boundary Fig. 1

2. Morphologies, seismicity and plate boundaries Deep-sea trench Mid-ocean ridge Fracture zone Fig. 2

3. Planform of thermal convection Downwelling Upwelling Benard (1901) Fig. 3

4. Surface velocities Poloidal component Toroidal component Bercovich (1995) Fig. 4

5. Earthquake = Faulting Normal fault Modified from Paterson (1958) Fig. 5

6. Fault parameters of an earthquake Fault plane strike dip angle rake or slip angle amount of slip f - y slip vector direction usinlcosd/ucosl = tan(f - y) cosdtanl = tan(f - y) Fig. 6

7. Focal mechanism of an earthquake Fig. 7a

8. Auxiliary plane Fault plane Fig. 7b

9. Slip vector and auxiliary plane Fig. 8

10. Age distribution of ocean floor Fig. 9 Sclater et al. (1981)

11. Ocean floor topography profile East Pacific Rise Tonga Trench Fig. 10

12. Formation of Oceanic Crust M.O.R. Basalt Melt Gabbro, Cumulates Moho Partial melting Detrick et al. (1987) Fig. 11

13. Decompressional melting Melting temperature Asthenosphere Start of melting Fig. 12

14. Magnetic anomaly stripes Atlantic Spreading axis Cox et al. (1967) Fig. 13

15. History of magnetic reversals Harland et al. (1982) Fig. 14

16. MOR activities at different spatial scales Basalts are altered (metamorphosed) by hydrothermal circulations. RIDGE Planning Office (1989) Fig. 15

17. Normal fault-type focal mechanisms Atlantic Sykes (1967) Fig. 16

18. Normal Faulting km Macdonald (1982) Fig. 17

19. Ridge-ridge transform fault M.O.R. Transform fault Fracture zone C ● D ● Plate A Plate B M.O.R. Fig. 18

20. Transform faults Atlantic Fracture zone Fig. 19

21. Fracture zone Delong et al. (1979) Fig. 20

22. Focal Mechanisms Engeln et al. (1986) Fig. 21

23. Continental rifting and sea-floor spreading Africa S. America Sibuet & Mascle (1978) Atlantic Fig. 22

24. Energy discippation Fig. 23

25. Trench-trench transform Fig. 24

26. Trench-trench type transform fault North Fiji Basin Vanuatu Tonga Fig. 25

27. Two types of convergent boundaries Collision zone Subduction zone Fig. 26

28. Subduction zone Indian Ocean Fig. 27

29. Tectonic elements in the subduction zone Karig (1974) Fig. 28

30. Three brothers: earthquakes in subduction zones Fig. 29

31. Eldest brother: 1994 Sanriku (Ms 7.6) Fig. 30 Nakayama & Takeo (1997)

32. Slip vectors Wei & Seno (1989) Fig. 31

33. Lubrication by pore fluid pressure s* = s - p w Effective stress Fig. 32

34. Seafloor topography in the outer-rise region Cardwell et al. (1976) Fig. 33

35. Trench – Outer rise earthquakes Tension ○: tension ●: compression Compression Seno and Yamanaka (1996) Seno and Gonzalez (1987) Fig. 34

36. Age/depth of outer-rise earthquakes Age of the plate (Ma) White: tension Depth Black: compression Seno and Yamanaka (1996) Fig. 35

37. Intermediate-depth earthquakes: Northern Honshu double seismic zone Matsuzawa et al. (1986) Fig. 36

38. Bonin arc Deep seismicity van der Hilst & Seno (1993) Fig. 37

39. Dehydration embrittlement: Serpentinite Raleigh & Paterson (1965) Fig. 38

40. Dehydration locus for slab seismicity (a) Cold slab type (b) Hot slab type Dehydration from crust Dehydration from crust Dehydration from serpentine Dehydration from serpentine Yamasaki & Seno (2003) Fig. 39

41. Active faults in Japan Fig. 40

42. Fault-types of active faults in Japan Reverse Strike-slip Normal Huzita (1980) Fig. 41

43. Volcanoes in Japan Volcanic front Fig. 42

44. Accretion: Offscarping at the toe of the trench Seely et al. (1974) Fig. 43

45. Accretionary prism at the Nankai Trough Trough axis Kuramoto et al. (2000) Decollement Fig. 44

46. Geological terranes of Japan Y. Saito (unpublished material) Fig. 45

47. Subduction zone Collision zone Fig. 46

48. Himalayas Himalayan Frontal Thrust Indus-Zangpo Suture Zone 300 km Molnar (1984) Fig. 47

49. Fig. 48 Tapponnier et al. (1982)