海底地形校正在正确拾取OBS震相中的重要作用*
作者简介:王建(1988—), 男, 湖南省株洲县人, 在读博士研究生, 主要从事海洋地球物理研究。E-mail: wangjian@scsio.ac.cn
收稿日期: 2016-10-27
要求修回日期: 2016-11-28
网络出版日期: 2017-09-22
基金资助
国家自然科学基金重大研究计划(91428204、91028002)
国家自然科学基金项目(41404050、41176053、41606064)
The importance of seafloor topographic correction in identifying and picking seismic phases of OBS
Received date: 2016-10-27
Request revised date: 2016-11-28
Online published: 2017-09-22
Supported by
Major Program of National Natural Science Foundation of China (91428204, 91028002)
Natural Science Foundation of China ( 41404050, 41176053, 41606064)
Copyright
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、PmP、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。
王建 , 赵明辉 , 张佳政 , 贺恩远 , 丘学林 . 海底地形校正在正确拾取OBS震相中的重要作用*[J]. 热带海洋学报, 2017 , 36(5) : 93 -100 . DOI: 10.11978/2016107
Ocean bottom seismometer (OBS) survey is a preferred way to detect deep crustal structures beneath seafloor. It is important to identify and pick reflected/refracted seismic phases correctly in OBS seismic record sections to obtain deep seismic structures. When OBS instruments are deployed on rugged seafloor, the propagating characteristics of seismic phases from the deep lithosphere, such as Pg, PmP and Pn, can be affected by undulated topography. For example, along the seismic line A4M4 cutting across the Zhenbei and Huangyan seamounts in the East Sub-basin of the South China Sea, and along the line Y3Y4 crossing the mid-ocean ridge in the Southwest India Ridge, the highly-varied reliefs increase the difficulty to identify seismic phases in the OBS record sections. Topographic correction is done to eliminate the effects of seafloor topography before picking the travel times of seismic phases. Seismic phases can be identified accurately after the correction according to different apparent velocities and propagating patterns of seismic phases. The method of seafloor topographic correction contributes greatly to recognizing seismic phases and studying crustal structures in these rough terrains, and it can provide references and experiences for the identification of OBS seismic phases in other areas with complex topography.
Fig. 1 Theoretical seismic phases for a normal oceanic crust. (a) Normal oceanic crustal model and ray-tracing paths; (b) theoretical travel-time curves of seismic phases. The velocities of seawater, sediment, Layer 2, Layer 3, and upper mantle are set to 1.5, 2.4-3.0, 3.4-6.4, 6.6-7.0, 7.8-8.0 km·s-1, respectively. The thicknesses of seawater, sediment, Layer 2 and Layer 3 are of 3.0, 1.5, 2.5, 3.5 km, respectively. The reduced travel time = (absolute travel time - distance/reduced velocity)/s, and the reduced velocity is 6.0 km·s-1图1 典型洋壳模型的理论震相展布图 |
Fig. 2 Bathymetric map of the East Sub-basin of the South China Sea and locations of OBSs. The gray circles indicate OBS stations; the thin white lines represent air-gun shooting tracks, and the bold white line represents seismic line A4M4图2 南海东部次海盆海底地形及OBS位置 |
Fig. 3 Bathymetry depth along the seismic line A4M4 in the East Sub-basin of the South China Sea图3 南海东部次海盆沿A4M4测线的水深 |
Fig. 4 Seismic record sections before and after topographic correction, ray-tracing and travel-times fitting for Station OBS05 along Profile A4M4. (a) The original seismic record section. Red line is the travel time of seismic wave passing through seawater, corresponding to the vertical ordinate on the right side; (b) seismic record section after topographic correction; (c) observed travel times (colored vertical error bars associated with uncertainties) compared to calculated travel times (black dots); (d) crust structure model and ray-tracing simulation, where different colored rays are comparable to the different colored travel times in (c). The reduced travel time = (absolute travel time - offset/reduced velocity)/s, and the reduced velocity is 6.0 km·s-1图4 A4M4剖面中OBS05台站地形校正前后地震记录剖面及射线追踪与走时模拟 |
Fig. 5 Seismic record sections before and after topographic correction, ray-tracing and travel-times fitting for Station OBS31 along Profile A4M4. Legends are the same as those in |
Fig. 6 Bathymetric map of the Southwest India Ridge and locations of OBSs. The gray circles indicate OBS stations; the thin white lines represent air-gun shooting tracks, and the bold white line represents seismic line Y3Y4图6 西南印度洋中脊海底地形及OBS位置 |
Fig. 7 Bathymetry depth along the seismic line Y3Y4 in the Southwest India Ridge图7 西南印度洋中脊沿Y3Y4测线的水深 |
Fig. 8 Seismic record sections before and after topographic correction, ray-tracing and travel-times fitting for Station OBS02 along Profile Y3Y4. Legends are the same as those in |
The authors have declared that no competing interests exist.
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[4] |
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[5] |
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[6] |
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[7] |
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[8] |
|
[9] |
|
[10] |
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[11] |
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[12] |
|
[13] |
|
[14] |
|
[15] |
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[16] |
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[17] |
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[18] |
|
[19] |
|
[20] |
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[21] |
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