The Correction of Shot and OBS Position in the 3D Seismic Experiment of the SW Indian Ocean Ridge
The Correction of Shot and OBS Position in the 3D Seismic Experiment of the SW Indian Ocean Ridge
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DOI：
10.1002/cjg2.1577
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发表时间：
2010-11
期刊：
影响因子：
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通讯作者：
W. Ao;Minghui Zhao;X. Qiu;Jiabiao Li;A. Ruan;Li Shoujun;Jiazheng Zhang
中科院分区：
文献类型：
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作者：
W. Ao;Minghui Zhao;X. Qiu;Jiabiao Li;A. Ruan;Li Shoujun;Jiazheng Zhang
在海上进行三维（3-D）地震实验时，由于船上GPS天线与海水中气枪震源中心的距离，以及风、海流等环境因素，测量船会调整其航向，导致炮弹的真实位置偏离预设的炮弹轨迹；同时，由于OBS属于自由落体类型，在下降过程中通常会受到海流的影响，OBS在海底的实际位置会偏离设计点（部署位置）。因此，气枪射击和海底地震仪（OBS）位置的校准是后续精细地震速度层析成像研究的基本步骤。我们的研究重点是利用西南印度洋海脊的新 3D 地震实验的最新数据来校正炮点和 OBS 位置。利用舰船航向、GPS天线和气枪阵列之间的几何关系修正射击位置。 OBS位置修正基于直达水波的传播时间，采用蒙特卡罗法和最小二乘法。此外，我们还讨论了直达水波的缩短走时曲线与OBS偏差之间的关系。结果表明，OBS位置普遍偏离设计点1km左右，误差范围为0~20m左右，镜头调整至实际位置。研究成果不仅为西南印度洋海脊三维地震层析成像提供了基础数据库，也为今后南海三维地震勘探提供了宝贵的经验。
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.