实测数据揭示海底地震仪上浮速率与出水点规律

Floating Rate and Sea Surface Outlet Point of Ocean Bottom Seismometer

使用海底地震仪(OBS)对极地浮冰区进行探测时,存在上浮的OBS被浮冰遮挡而难以发现和回收等困难,为提高两极浮冰区海底地震探测效率,亟需对OBS上浮出水时间和位置进行较为准确地预测.本研究以2019年南海OBS观测、2020年西太平洋OBS探测以及2011年南海东部次海盆三维OBS探测现场作业的实测距离和位置信息等数据为基础,分析了OBS上浮速率、投放点和出水点的特征,开展了OBS在水中下沉和上浮的运动过程研究,总结了OBS出水点的分布规律.结果表明:(1)在垂直方向上,OBS上浮速率近似匀速,可用平均速率代替,进而可精确计算上浮出水时间;(2)OBS在海底的位置与投放位置的偏移距随机分布,这表明投放点水深与重定位偏移距离无明显线性相关性;(3)OBS上浮出水点与投放点有重合的趋势,两者距离在300 m以内的概率大于31%,两者距离在500 m以内的概率大于59%.

Ocean bottom seismometer(OBS) active and passive experiments are the most useful methods to reveal crustal and upper mantle structures under the ocean, but till now, few OBS experiments have been done in the Arctic and Antarctica, where the main challenges are finding and recovering the OBSs sheltered by the high coverage rate of floating ices. For the forthcoming OBS experiments in the polar regions, it is necessary to study the time and the location of OBS surfacing to the sea(outlet position). To reveal the process of OBS sinking and floating in the sea and to find the law of OBS’s outlet position, we use the information of the up-floating rate, deployment position and recovery position of OBS during three expeditions of the 2019 South China Sea OBS observation, 2020 Western Pacific OBS experiment and 2011 the South China Sea three-dimension OBS experiment in this study. The main results are as follows:(1) The OBS shows stable up-floating rate in the vertical direction,which will be helpful to predict the moment of OBS surfacing to the sea;(2) the OBS locations on the sea bottom are randomly distributed with the offset of the drop location, which indicates that the water depth at the drop point has no obvious linear correlation with the relocation offset distance;(3) the outlet position and deployment position of OBS suggest very close distance,with a statistical estimate of <300 meters(31%) and <500 meters(59%).