The correction of shot and OBS position in the 3D seismic experiment of the SW Indian Ocean Ridge

In a three-dimensional (3-D) seismic experiment carried out at sea, due to the distance between GPS antenna on ship and the center of air gun sources in sea water, and some environmental factors such as wind and sea current, the survey ship would adjust its heading direction which causes the shot's real position to deviate from presupposed shot track; meanwhile, real locations of OBSs on the seafloor would drift from designed points (deployed locations) since OBSs are of free-fall type and are usually affected by sea current during descending. So, the calibration of air gun shot and Ocean Bottom Seismometer (OBS) locations are basic steps for later studies on fine seismic velocity tomography. Our research focuses on the correction of shot and OBS positions with latest data from a new 3D seismic experiment in the SW Indian Ocean Ridge. The shot positions were corrected with geometric relationship among ship's heading, GPS antenna and the air gun array. The correction of OBS positions was based on travel times of direct water waves, and Monte Carlo and Least Square Methods were adopted. In addition, we discuss the relationship between reduced travel time curve of direct water wave and OBS deviation. Our results show that OBS locations generally drifted from the design points about 1 km, with an error range of 0 similar to 20 m and shots were adjusted to their actual positions. The research results do not only supply a fundamental database for the 3D seismic tomography in SW Indian Ocean Ridge, but also provide valuable experiences for 3D seismic survey in the South China Sea in future.