One of aims of crustal structural expedition is to obtain P-wave velocity structures underneath the ocean bottom. Seismic data used here are deep penetrating refraction and wide-angle reflection waves generated by a large airgun array system. Ocean Bottom Seismographs (OBS) are settled on the sea bottom and positioned by using a real time super short base line (SSBL) acoustic positioning system with accuracy of 1-3% of water depth. Since we have required a high resolution seismic image, a super-densely deployed OBS array with spacing of a few to 10 km is preferred. These seismic methods using OBS can be used for understanding of deeper structure.
Survey Specification
SOURCE : Airgun (Bolt Technology Inc.)
Shot Interval : 100-200m
Total Volume : 12000cu.in.[200L] (1999-) / 4000cu.in.[66L](-1998)
Pressure : 2000psi
Ocean Bottom Seismograph (OBS) :
Maximum Depth : 6000m
Sensor : Three-component Geophone & Hydrophone
[One vertical and two horizontal components, Natural frequency:4.5Hz, Sensitivity:0.69V/inch/s(OPEN)]
Recording System : Sampling continuously (Timer control is possible for start time.)
Recording Media : DAT(digital audiotape) or Hard Disk
Sampling Rate : 100Hz
Power : Rechargeable lithium-ion or alkali battery
Accoustic Communication & Release System: Transponder,Transducer, Forced electrochemical erosion
Attached Parts : Weight, Flush light, Radio beacon
Pressure Resistant Container : 17 inch glass sphere
| OBS Cruise List | ||||||||
|---|---|---|---|---|---|---|---|---|
| Year | Cruise ID | Survey Area | The Number of OBSs | Period | Deploy ment |
Shooting | Retrival | Method |
| 1997 | KR97-04 | Off Muroto, Nankai Trough | 25 | Jun.25.-Jul.22. | * | * | * | MCS OBS GM |
| 1997 | KR97-07 | Off Miyako, Japan Trench | 26 | Sep.30.-Oct.16. | * | * | * | MCS OBS GM |
| 1998 | KR98-04 | Off Miyagi, Japan Trench | 15 | Apr.16.-May.05. | * | * | * | MCS OBS GM |
| 1998 | KR98-06 | Off Shikoku - Kumano, Nankai Trough | 14 | Jun.06-Jul.08. | * | * | * | MCS OBS GM |
| 1998 | KR98-10 | Off Muroto, Nankai Trough | 15 | Oct.07.-Oct.23. | * | * | MCS OBS GM |
|
| 1998 | KY98-13 | Off Muroto, Nankai Trough | 15 | Oct.31.-Nov.07. | * | OBS | ||
| 1999 | KR99-04 | Off Muroto, Nankai Trough | 38 | May.02.-Jun.10. | * | MCS OBS GM |
||
| 1999 | KY99-03 | Off Muroto, Nankai Trough | 98 | Jun.01.-Jun.30. | * | * | * | OBS |
| 1999 | KY99-05 | Off Miyagi, Japan Trench | 39 | Jul.20.-Aug.20. | * | * | * | OBS |
| 2000 | KY00-02 | Off Aomori, Japan Trench | 46 | May.29.-Jun.23. | * | * | * | OBS |
| 2000 | KY00-05 | Off Nemuro, Kuril Trench / Okhotsk Sea | 45 | Jul.16.-Aug.14. | * | * | * | OBS |
| 2000 | KY00-08 | Off Miyake-jima / Kozu-shima | 77 | Oct.26.-Nov.05. | * | * | * | OBS |
| 2001 | KY01-06 | Off Tokai, Nankai Trough | 170 | Jul.29.-Sep.06. | * | * | * | OBS |
| 2002 | KY02-09 Leg 1 |
Off Tottori, Japan Sea | 35 | Aug.25.-Sep.07. | * | * | * | OBS |
| 2002 | KY02-09 Leg 2 |
Off Kumano, Nankai Trough | 5 | Sep.08.-Sep.24. | * | * | * | MCS OBS |
| 2003 | KY03-01 Leg 1 |
Middle Mariana Area | 106 | Jan.09.-Feb.01. | * | * | * | OBS |
| 2003 | KY03-06 Leg 2 |
Middle Mariana Area | 46 | Jun.28.-Jul.16. | * | * | * | OBS |
| 2003 | KR03-09 | Off Sanriku, Japan Trench | 60 | Aug.06.-Aug.28. | * | * | * | MCS OBS GM |
| 2004 | KY04-01 | Off Kii Peninsula, Nankai Trough | 100 | Jan.11.-Feb.12. | * | * | * | OBS |
| 2004 | KR04-10 Leg 1 |
Off Miyagi, Japan Trench | 72 | Aug.06.-Aug.19. | * | * | OBS GM |
|
| 2004 | KY04-13 | Off Kii Peninsula, Nankai Trough | 110 | Nov.10.-Nov.29. | * | * | * | OBS |
| 2006 | KY06-13 | Off Kii Peninsula, Nankai Trough | 90 | Nov.07.-Dec.02. | * | * | * | OBS |
| 2007 | KR07-10 | Nankai Trough | 78 | Jul.28.-Aug.16. | * | * | * | OBS GM |
| 2007 | KR07-E01 | off Niigata, Japan sea | 40 | Aug.18.-Aug.28. | * | * | * | MCS OBS GM |
| 2008 | KY08-04 | Izu-Bonin Arc | 110 | May.14.-Jun.09. | * | * | * | OBS |
| 2008 | KR08-09 | Izu-Bonin Arc / Off Kumano |
85 | Jul.27.-Aug.12. | * | * | MCS OBS GM |
|
| 2008 | KY08-08 | Izu-Bonin Arc | 85 | Aug.14.-Aug.28. | * | * | OBS | |
| 2008 | KY08-E03 | Izu-Bonin Arc | 61 | Nov.06.-Nov.21. | * | * | OBS | |
| 2008 | KR08-16 | Nankai Trough, Hyuganada | 160 | Dec.07.-Dec.26. | * | * | OBS GM |
|
| 2009 | KY09-E01 | Nankai Trough, Hyuganada | 160 | Jan.14.-Jan.28. | * | OBS | ||
| 2009 | KR09-06 | NW Pacific | 90 | Jun.19-Jul.05. | * | * | MCS OBS GM |
|
| 2009 | KY09-03 | NW Pacific | 90 | Jul.05.-Jul.21. | * | OBS | ||
| 2009 | KY09-06 | Eastern Margin of Japan Sea |
30 | Aug.06-Aug.19. | * | * | * | OBS |
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