海底地形校正在正确拾取OBS震相中的重要作用
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摘要
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 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, Pm P 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.
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, Pm P 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.
引文
李振五,1984.南海中部和北部地壳性质的探讨[J].地球物理学报,27(2):153-166.LI ZHENWU,1984.A discussion on the crustal nature of the central and northern parts of South China Sea[J].Acta Geophysica Sinica,27(2):153-166(in Chinese).
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王绪本,李永年,高永才,1999.大地电磁测深二维地形影响及其校正方法研究[J].物探化探计算技术,21(4):327-332.WANG XUBEN,LI YONGNIAN,GAO YONGCAI,1999.Two dimensional topographic responses in magneto-telluric sounding and its correction methods[J].Computing Techniques for Geophysical and Geochemical Exploration,21(4):327-332(in Chinese).
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张莉,赵明辉,王建,等,2013.南海中央次海盆OBS位置校正及三维地震探测新进展[J].地球科学--中国地质大学学报,38(1):33-42.ZHANG LI,ZHAO MINGHUI,WANGJIAN,et al,2013.Correction of OBS position and recent advances of 3D seismic exploration in the Central Sub-basin of South China Sea[J].Earth Science--Journal of China University of Geosciences,38(1):33-42(in Chinese).
张玮,魏正宇,张双狮,等,2011.高密度电阻率法探测汶川地震造成的不稳定斜坡[J].工程勘察,39(11):90-94.ZHANGWEI,WEI ZHENGYU,ZHANG SHUANGSHI,et al,2011.High density resistivity method detect unstable slope created by Wenchuan earthquake[J].Geotechnical Investigation&Surveying,39(11):90-94(in Chinese).
赵明辉,丘学林,夏戡原,等,2004.南海东北部海陆联测地震数据处理及初步结果[J].热带海洋学报,23(1):58-63.ZHAOMINGHUI,QIU XUELIN,XIA KANYUAN,et al,2004.Onshore-offshore seismic data processing and preliminary results in NE South China Sea[J].Journal of Tropical Oceanography,23(1):58-63(in Chinese).
赵明辉,丘学林,李家彪,等,2010.慢速、超慢速扩张洋中脊三维地震结构研究进展与展望[J].热带海洋学报,29(6):1-7.ZHAO MINGHUI,QIU XUELIN,LI JIAOBIAO,et al,2010.Research development and prospect on three-dimensional seismic structures of slow and ultraslow spreading ocean ridges[J].Journal of Tropical Oceanography,29(6):1-7(in Chinese).
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COHEN J K,STOCKWELL J W JR,1995.The SU User’s Manual[M].Colorado:Colorado School of Mines:1-40.
HE ENYUAN,ZHAO MINGHUI,QIU XUELIN,et al,2016.Crustal structure across the post-spreading magmatic ridge of the East Sub-basin in the South China Sea:Tectonic significance[J].Journal of Asian Earth Sciences,121:139-152.
JIANG KANG,HU CHANGMIAO,YU KAI,et al,2014.Landsat TM/ETM+topographic correction method based on smoothed terrain and semi-empirical model[J].Journal of Remote Sensing,18(2):287-306.
LUDWIG W J,KUMAR N,HOUTZ R E,1979.ProfilerSonobuoy measurements in the South China Sea Basin[J].Journal of Geophysical Research,84(B7):3505-3518.
NISSEN S S,HAYES D E,BUHL P,et al,1995.Deep penetration seismic soundings across the northern margin of the South China Sea[J].Journal of Geophysical Research,100(B11):22407-22433.
QIU XUELIN,SHI XIAOBIN,YAN PIN,et al,2003.Recent progress of deep seismic experiments and studies of crustal structure in northern South China Sea[J].Progress in Natural Science,13(7):481-488.
WANG JIAN,ZHAO MINGHUI,QIU XUELIN,et al,2016.3Dseismic structure of the Zhenbei-Huangyan seamounts chain in the East Sub-basin of the South China Sea and its mechanism of formation[J].Geological Journal,51(S1):448-463,doi:10.1002/gj.2781.
WHITE R S,MCKENZIE D,O'NIONS R K,1992.Oceanic crustal thickness from seismic measurements and rare earth element inversions[J].Journal of Geophysical Research,97(B13):19683-19715.
WILLIAM C T,JOSEPH E T,1991.SAC-Seismic Analysis Code Users Manual[M].Livermore,CA:Lawrence Livermore National Laboratory.
ZELT C A,SMITH R B,1992.Seismic traveltime inversion for2-D crustal velocity structure[J].Geophysical Journal International,108(1):16-34.
ZHANG JIAZHENG,ZHAO MINGHUI,QIU XUELIN,et al,2013.Seismic phases from the Moho and its implication on the ultra-slow spreading ridge[J].Acta Oceanologica Sinica,32(12):75-86.
ZHANG JIE,LI JIABIAO,RUAN AIGUO,et al,2016.The velocity structure of a fossil spreading Centre in the Southwest Sub-basin,South China Sea[J].Geological Journal,51(S1):548-561,doi:10.1002/gj.2778.
丘学林,赵明辉,徐辉龙,等,2012.南海深地震探测的重要科学进程:回顾和展望[J].热带海洋学报,31(3):1-9.QIUXUELIN,ZHAO MINGHUI,XU HUILONG,et al,2012.Important processes of deep seismic surveys in the South China Sea:retrospection and expectation[J].Journal of Tropical Oceanography,31(3):1-9(in Chinese).
王绪本,李永年,高永才,1999.大地电磁测深二维地形影响及其校正方法研究[J].物探化探计算技术,21(4):327-332.WANG XUBEN,LI YONGNIAN,GAO YONGCAI,1999.Two dimensional topographic responses in magneto-telluric sounding and its correction methods[J].Computing Techniques for Geophysical and Geochemical Exploration,21(4):327-332(in Chinese).
姚伯初,曾维军,HAYES D E,等,1994.中美合作调研南海地质专报[M].武汉:中国地质大学出版社.YAO BOCHU,ZENG WEIJUN,HAYES D E,et al,1994.The Geological Memoir of South China Sea Surveyed Jointly by China&USA[M].Wuhan:China University of Geosciences Press(in Chinese).
张莉,赵明辉,王建,等,2013.南海中央次海盆OBS位置校正及三维地震探测新进展[J].地球科学--中国地质大学学报,38(1):33-42.ZHANG LI,ZHAO MINGHUI,WANGJIAN,et al,2013.Correction of OBS position and recent advances of 3D seismic exploration in the Central Sub-basin of South China Sea[J].Earth Science--Journal of China University of Geosciences,38(1):33-42(in Chinese).
张玮,魏正宇,张双狮,等,2011.高密度电阻率法探测汶川地震造成的不稳定斜坡[J].工程勘察,39(11):90-94.ZHANGWEI,WEI ZHENGYU,ZHANG SHUANGSHI,et al,2011.High density resistivity method detect unstable slope created by Wenchuan earthquake[J].Geotechnical Investigation&Surveying,39(11):90-94(in Chinese).
赵明辉,丘学林,夏戡原,等,2004.南海东北部海陆联测地震数据处理及初步结果[J].热带海洋学报,23(1):58-63.ZHAOMINGHUI,QIU XUELIN,XIA KANYUAN,et al,2004.Onshore-offshore seismic data processing and preliminary results in NE South China Sea[J].Journal of Tropical Oceanography,23(1):58-63(in Chinese).
赵明辉,丘学林,李家彪,等,2010.慢速、超慢速扩张洋中脊三维地震结构研究进展与展望[J].热带海洋学报,29(6):1-7.ZHAO MINGHUI,QIU XUELIN,LI JIAOBIAO,et al,2010.Research development and prospect on three-dimensional seismic structures of slow and ultraslow spreading ocean ridges[J].Journal of Tropical Oceanography,29(6):1-7(in Chinese).
BARRY K M,CAVERS D A,KNEALE C W,1975.Recommended standards for digital tape formats[J].Geophysics,40(2):344-352.
COHEN J K,STOCKWELL J W JR,1995.The SU User’s Manual[M].Colorado:Colorado School of Mines:1-40.
HE ENYUAN,ZHAO MINGHUI,QIU XUELIN,et al,2016.Crustal structure across the post-spreading magmatic ridge of the East Sub-basin in the South China Sea:Tectonic significance[J].Journal of Asian Earth Sciences,121:139-152.
JIANG KANG,HU CHANGMIAO,YU KAI,et al,2014.Landsat TM/ETM+topographic correction method based on smoothed terrain and semi-empirical model[J].Journal of Remote Sensing,18(2):287-306.
LUDWIG W J,KUMAR N,HOUTZ R E,1979.ProfilerSonobuoy measurements in the South China Sea Basin[J].Journal of Geophysical Research,84(B7):3505-3518.
NISSEN S S,HAYES D E,BUHL P,et al,1995.Deep penetration seismic soundings across the northern margin of the South China Sea[J].Journal of Geophysical Research,100(B11):22407-22433.
QIU XUELIN,SHI XIAOBIN,YAN PIN,et al,2003.Recent progress of deep seismic experiments and studies of crustal structure in northern South China Sea[J].Progress in Natural Science,13(7):481-488.
WANG JIAN,ZHAO MINGHUI,QIU XUELIN,et al,2016.3Dseismic structure of the Zhenbei-Huangyan seamounts chain in the East Sub-basin of the South China Sea and its mechanism of formation[J].Geological Journal,51(S1):448-463,doi:10.1002/gj.2781.
WHITE R S,MCKENZIE D,O'NIONS R K,1992.Oceanic crustal thickness from seismic measurements and rare earth element inversions[J].Journal of Geophysical Research,97(B13):19683-19715.
WILLIAM C T,JOSEPH E T,1991.SAC-Seismic Analysis Code Users Manual[M].Livermore,CA:Lawrence Livermore National Laboratory.
ZELT C A,SMITH R B,1992.Seismic traveltime inversion for2-D crustal velocity structure[J].Geophysical Journal International,108(1):16-34.
ZHANG JIAZHENG,ZHAO MINGHUI,QIU XUELIN,et al,2013.Seismic phases from the Moho and its implication on the ultra-slow spreading ridge[J].Acta Oceanologica Sinica,32(12):75-86.
ZHANG JIE,LI JIABIAO,RUAN AIGUO,et al,2016.The velocity structure of a fossil spreading Centre in the Southwest Sub-basin,South China Sea[J].Geological Journal,51(S1):548-561,doi:10.1002/gj.2778.