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The earthquakes occurred underneath the ocean bottom can be observed on land, but the size of detectable earthquakes has the limit and focal distribution cannot know accurately.
Observations by the ocean bottom seismograph (OBS) allow to detect the microearthquakes occurred underneath the sea floor and obtain the accurate focal distribution.

Survey Specification

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 errosion
Attached Parts : Weight, Flush light, Radio beacon
Pressure Resistant Container : 17 inch glass sphere

Earthquake Observations
Year Survey Area The
Number
of OBSs		   Period (Cruise ID)
2010 Off Shikoku - Kii / Nankai Trough 154+20 deploy Oct.13-Nov.10.2010 (KR10-11)
retrieve Dec.20-Dec.29.2010 (NT10-21) /
Jan.04-Jan.22.2011 (NT11-01)
Jul.15-Jul.23.2011 (NT11-12) /
Sep.13-Oct.10,.2011 (KR11-09)
2009 Off Shikoku / Nankai Trough 180+21 deploy Sep.30-Oct.20.2009 (KR09-14)
retrieve Jan.28-Feb.17.2010 (KY10-02)
Jun.16-Jun.22.2010(KY10-08)
2008 Hyuganada / Nankai Trough 160 deploy Dec.7.-Dec.26.2008 (KR08-16)
retrieve Jan.14.-Jan.28.2009 (KY09-E01)
Off Kii Peninsula / Nankai Trough 39 deploy Jul.24.-Jul.31.2008 (KY08-06)
retrieve Oct.7.-Oct.12.2008 (KY08-11)
2006 Northern Izu-Bonin
(Hachijojima-Torishima) 2 		3 deploy July.18.-Jul.30.2006 (KY06-08)
retrieve Sep.30.-Oct.25.2006 (KR06-13)
Northern Izu-Bonin
(Hachijojima-Torishima) 1 		36 deploy Apr.19.-Apr.28.2006 (KY06-05)
retrieve July.18.-Jul.30.2006 (KY06-08)
2005 Off Shima Peninsula / Nankai Trough 28 deploy Mar.12.-Mar.18.2005 (KY05-03)
retrieve Jun.3.-Jun.10.2005 (NT05-07)
2004 Off Kochi / Nankai Trough 27 deploy Mar.8.-Mar.16.2004 (KY04-03)
retrieve May.23.-May.30.2004 (KY04-05)
2003 Off Kii Peninsula / Nankai Trough 30 deploy Mar.8.-Mar.15.2003 (KY03-03)
retrieve May.23.-May.30.2003 (KY03-05)
2001 Nankai Trough / Off Kumano 24 deploy Nov.4.-Dec.3.2001 (KR01-14)
retrieve Feb.4.-Feb.13.2002 (KY02-02)

Click the Area name, you can move to each cruise page.

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