OBS(Ocean Bottom Seismograph)
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.