The Correction of Shot and OBS Position in the 3D Seismic Experiment of the SW Indian Ocean Ridge

Abstract

AbstractIn a three‐dimensional (3D) 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 may adjust its heading direction, which makes the real shot position deviate from designed shot track; meanwhile, the real locations of Ocean Bottom Seismometers (OBS)s on the seafloor may drift from designed points (deployed locations) since OBSs are of free‐fall type and usually affected by sea currents during its descending. So, the calibration of air‐gun shots and OBSs' positions are basic steps for later studies on fine seismic velocity tomography. Our research is mainly focused on the correction of shot and OBS positions with up‐to‐date 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 air‐gun array. The correction of OBS positions were based on travel time of direct water wave, Monte Carlo method and least square method. In addition, we discuss the relationship between reduced travel time curves of direct water wave and OBS's deviation. Our results show that OBS's locations generally drift from the designed points about 1 km with an error range of 0~20 m, and shots are adjusted to its actual positions. The correction results not only supply a fundamental database for the 3D seismic tomography in our study area, but also provide valuable experiences for 3D seismic survey in the South China Sea in future.