Abstract The relocation of ocean bottom seismometers (OBSs) is a key step in analyzing the three-dimensional seismic tomographic structure of crust and mantle. In order to get the accurate location of OBSs on the seafloor, we analyze the travel times of direct water waves emitted by air-guns. The Monte Carlo and least square methods have been adopted to calculate the true OBS location. The secondary time correction is necessary if the arrivals of direct water waves show overall time drift during relocation which maybe originates from remnant of linear clock drift correction and average errors of travel time picking, mean water velocity assumption, and experiment geometry. We have improved the original OBS relocation procedure which we used previously for other experiments by deliberateness of a secondary time correction and automatically approaching the really mean water velocity. A series of synthetic tests are carried out firstly to document the feasibility of our procedure and then it is applied on a real experiment. In here, we relocate 28 OBSs in total were relocated in 3D seismic survey near Bashi Channel. Relocation results show that the drifting distances for the 28 OBSs range from 65 to 1136 m between the deployed and relocated locations deduced by relocation results. The Pearson correlation coefficient between OBS drifting direction and sea current direction is 0.79, indicating that the two sets of data are highly linearly related and further manifest the sea current as the most possible driving force for OBS drifting during landing on the seafloor but its detailed influence mechanism is unclear by now. This research is necessary and critical for velocity structure modeling, and the optimal relocation program provides valuable experiences for 3D seismic survey in other area.

中文翻译：

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最小二乘法和蒙特卡洛法相结合的OBS重定位在巴士海峡附近3D地震勘测中

摘要 海底地震仪（OBSs）的重定位是分析地壳地幔三维地震层析结构的关键步骤。为了获得OBS在海底的准确位置，我们分析了气枪发射的直接水波的传播时间。采用蒙特卡罗和最小二乘法计算真实的 OBS 位置。如果直接水波的到达在重定位过程中表现出整体时间漂移，这可能源于线性时钟漂移校正的残余和走时拾取的平均误差，平均水速假设和实验几何，则需要二次时间校正。我们已经改进了我们之前用于其他实验的原始 OBS 重定位程序，通过故意进行二次时间校正并自动接近真正的平均水流速度。首先进行了一系列综合测试以证明我们程序的可行性，然后将其应用于实际实验。在这里，我们在巴士海峡附近的 3D 地震调查中总共重新安置了 28 个 OBS。搬迁结果表明，根据搬迁结果推导出的28个OBS在部署和搬迁地点之间的漂移距离为65～1136 m。OBS漂流方向与海流方向的Pearson相关系数为0.79，表明两组数据呈高度线性相关，进一步表明海流是OBS在海底着陆时漂移的最可能驱动力，但其具体影响机制目前尚不清楚。这项研究对于速度结构建模是必要和关键的，优化重定位方案为其他地区的 3D 地震勘探提供了宝贵的经验。