海底地形校正在正确拾取OBS震相中的重要作用

The importance of seafloor topographic correction in identifying and picking seismic phases of OBS

海底地震仪(ocean bottom seismometer,OBS)探测是获得海底深部地壳结构的首选方法。正确拾取OBS记录中折射/反射震相,对获得准确的深部速度结构非常重要。当OBS布设在崎岖海底时,起伏的海底地形会影响OBS地震记录剖面中Pg、Pm P、Pn等岩石圈内部震相的展布特征,如南海东部次海盆中横穿珍贝-黄岩海山链的A4M4地震测线和西南印度洋中脊横穿扩张脊的Y3Y4测线,强烈的地形高差变化增加了这些测线上OBS台站地震剖面的震相识别难度。在震相拾取之前,通过地形校正方法消除海底地形对震相的影响;地形校正后,根据震相视速度及其展布趋势可以准确地识别震相,有效地提高了震相识别的可靠性。地形校正方法在上述地区的震相识别与速度结构研究方面发挥了重要作用,同时为今后在其他地形变化复杂地区的OBS震相识别提供了经验与借鉴。

Ocean bottom seismometer(OBS)survey is a preferred way to detect deep crustal structures beneath seafloor.It isimportant to identify and pick reflected/refracted seismic phases correctly in OBS seismic record sections to obtain deepseismic structures.When OBS instruments are deployed on rugged seafloor,the propagating characteristics of seismic phasesfrom the deep lithosphere,such as Pg,PmP and Pn,can be affected by undulated topography.For example,along the seismicline A4M4cutting across the Zhenbei and Huangyan seamounts in the East Sub-basin of the South China Sea,and along theline Y3Y4crossing the mid-ocean ridge in the Southwest India Ridge,the highly-varied reliefs increase the difficulty toidentify seismic phases in the OBS record sections.Topographic correction is done to eliminate the effects of seafloortopography before picking the travel times of seismic phases.Seismic phases can be identified accurately after the correctionaccording to different apparent velocities and propagating patterns of seismic phases.The method of seafloor topographiccorrection contributes greatly to recognizing seismic phases and studying crustal structures in these rough terrains,and it canprovide references and experiences for the identification of OBS seismic phases in other areas with complex topography.