Seismic survey using Ultra-Deep OBS in the Japan Trench axis area

We have developed “Ultra-Deep OBS (Ocean Bottom Seismograph)” which can be used in 9000 m of water depth. In January 2013, we conducted a seismic survey using two Ultra-Deep OBSs in the Japan Trench axis area off Miyagi, northeastern Japan. The survey was planned to obtain reflection seismic images and velocity structure around the drill site C0019 by the Integrated Ocean Drilling Program. One of Ultra-Deep OBSs was deployed near the drill site at ~6900 m water depth, and the other was deployed on the vicinity of trench axis at ~7500 m water depth. The OBSs recorded the seismic waves emitted from R/V Kairei’s tuned air gun array with 7800 inch which was fired every 50 m along the survey lines. The OBS data shows several phases, e.g., direct water wave arrival, refraction from oceanic crust. The data contains noises from previous shot signal but they can be cleaned up with time shift and dip filters. The OBS data will be incorporated into the velocity modeling during the reflection data processing. The Ultra-Deep OBS will make it possible to conduct seismological surveys in the extremely deep oceans with resolution comparable to surveys in the shallower oceans.