海底地震仪实测信号特性分析
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摘要
置于海底数百米至数千米的海底地震仪(OBS)的实测信号相比陆地地震仪具有不同的特性;由于水的作用或记录信号源频率的不同,短周期OBS和宽频带OBS记录的信号又有明显的差异。文章对南海西南次海盆地震探测期间记录的人工气枪震源和天然地震实测信号进行了时频分析,结果如下。1)气枪作业后在海底激发两种噪声:一是水的波动不断叠加形成的长波,周期50s左右,以水平分量为主;二是高频噪声,主要是OBS底座细微晃动引起的。2)宽频OBS对于水下移动目标激发海底波动具有很好的探测能力,特别是水平分量可以获得大振幅且周期特征清晰的记录,并能够指示方向。3)宽频OBS能记录到清晰的天然地震信号,为研究调查区岩石圈结构增添了更多的信息,短周期OBS对远震直达P波有很好的记录。国产宽频I-4C型OBS碰巧记录了日本M9.0级大震。
Seismic signals of ocean bottom seismometer(OBS) on the seafloor hundreds or thousands meters deep are different from those of land seismometer.The records of short-period OBS are also obviously different from those of broad-band OBS due to effects of sea water or signal frequency.This study carried out time-frequency analysis and compared the seismic signals excited by air gun as well as earthquake signals of OBS during a seismic survey in the southwest sub-basin of the South China Sea.The results are as follows.1) Air-gun shooting generated two kinds of noises: one is long-wave noise due to the superposition of water fluctuation,with a period of 50s mainly in the horizontal component;the other is high-frequency noise,mainly due to fin vibration of OBS pedestal itself.2) Broad-band OBS is able to detect the fluctuation caused by moving object under water,especially in the horizontal component whose amplitude is large and whose frequency feature is clear,from which the direction of the signal source can be distinguished.3) During this survey broad-band OBS recorded many high-quality earthquakes that will benefit our study on the lithosphere structure of the survey area,while short-period OBS had also obtained direct P-wave arrivals clearly.The I-4C type OBS happened to record the catastrophe earthquake of M9.0 occurred near Japan in March 2011.
Seismic signals of ocean bottom seismometer(OBS) on the seafloor hundreds or thousands meters deep are different from those of land seismometer.The records of short-period OBS are also obviously different from those of broad-band OBS due to effects of sea water or signal frequency.This study carried out time-frequency analysis and compared the seismic signals excited by air gun as well as earthquake signals of OBS during a seismic survey in the southwest sub-basin of the South China Sea.The results are as follows.1) Air-gun shooting generated two kinds of noises: one is long-wave noise due to the superposition of water fluctuation,with a period of 50s mainly in the horizontal component;the other is high-frequency noise,mainly due to fin vibration of OBS pedestal itself.2) Broad-band OBS is able to detect the fluctuation caused by moving object under water,especially in the horizontal component whose amplitude is large and whose frequency feature is clear,from which the direction of the signal source can be distinguished.3) During this survey broad-band OBS recorded many high-quality earthquakes that will benefit our study on the lithosphere structure of the survey area,while short-period OBS had also obtained direct P-wave arrivals clearly.The I-4C type OBS happened to record the catastrophe earthquake of M9.0 occurred near Japan in March 2011.
引文
[1]阮爱国,李家彪,冯占英,等.海底地震仪及其国内外发展现状[J].东海海洋,2004,22(2):19-27.
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[7]吴振利,李家彪,阮爱国,等.南海西北次海盆地壳结构:海底广角地震试验结果[J].中国科学:D辑,2011,41(10):1463-1476.
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[10]卫小冬,赵明辉,阮爱国,等.南海中北部OBS2006-3地震剖面中横波的识别与应用[J].热带海洋学报,2010,29(5):72-80.
[11]阮爱国,丘学林,李家彪,等.中国海洋深地震探测与研究进展[J].华南地震,2009,29(2):10-18.
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[13]QIU XL,CHEN Y,ZHU RX,et a1.The application of largevolume airgun sources to the onshore-offshore seismicsurveys:Implication from the experimental results innorthern South China Sea[J].Chinese Science Bulletin,2007,52(4):553-560.
[14]赵明辉,丘学林,夏少红,等.大容量气枪震源及其波形特征[J].地球物理学报,2008,51(2):558-565.
[15]CHANG E T Y,HSU S K,LEE C S.Earthquake swarmrecorded by an ocean bottom seismic array in southwestoffshore of Taiwan in October,2005[J].Terr Atmos Ocean Sci,2008,19:717-728,doi:10.3319/TAO.2008.19.6.717(PT).
[16]游庆瑜,刘福田,冉崇荣,等.高频微功耗海底地震仪研制[J].地球物理学进展,2003,18(1):173-176.
[17]王嘹亮,张志荣,阎贫,等.潮汕坳陷地壳结构探测初步成果[J].南海地质研究,2004,15:62-67.
[18]游庆瑜,刘福田,冉崇荣.MCI微功耗宽频带数字地震仪[J].地球物理学报,2003,46(3):347-354.
[19]罗文造,阎贫,温宁,等.南海北部潮汕坳陷海区海底地震仪调查实验[J].热带海洋学报,2009,28(4):59-65.
[20]BROCHER T M,PARSONS T,CREAGER K C,et al.Wide-angle seismic recordings from the 1998 SeismicHazards Investigation of Puget Sound(SHIPS),WesternWashington and British Columbia[R]//U.S.GeologicalSurvey Open-File Report,1999:129-314.
[21]TODA SHINJI,LIN JIAN,STEIN R S.Using the 2011M=9.0 Tohoku earthquake to test the Coulomb stresstriggering hypothesis and to calculate faults brought closer tofailure[J].Earth Planets and Space,2011,(63):725-730.
[22]邹立晔.地震震相分析与测量的进展[J].国际地震动态,2004,(10):1-8.
[23]STORCHAK D A,SCHWEITZER J,BORMANN P.TheIASPEI standard seismic phase list[J].SeismologicalResearch Letters,2003,74(6):791-772.
[2]牛雄伟,阮爱国,李家彪,等.洋中脊构造及地震调查现状[J].华南地震,2009,29(4):72-84.
[3]李湘云,吴振利,薛彬,等.SEDIS IV型短周期自浮式海底地震仪及应用体会[J].热带海洋学报,2007,26(5):35-39.
[4]阮爱国,李家彪,陈永顺,等.国产I-4C型OBS在西南印度洋中脊的试验[J].地球物理学报,2010,53(4):1015-1018.
[5]阮爱国,牛雄伟,吴振利,等.潮汕坳陷中生代沉积的折射波2D速度结构和密度[J].高校地质学报,2009,15(4):522-528.
[6]吴振利,阮爱国,李家彪,等.南海南部海底地震仪试验及初步结果[J].海洋学研究,2010,28(1):55-60.
[7]吴振利,李家彪,阮爱国,等.南海西北次海盆地壳结构:海底广角地震试验结果[J].中国科学:D辑,2011,41(10):1463-1476.
[8]敖威,赵明辉,阮爱国,丘学林.利用海底地震仪数据分析台风对海底环境噪音的影响[J].热带海洋学报,2009,28(6):61-67.
[9]敖威,赵明辉,丘学林,等.西南印度洋中脊三维地震探测中炮点与海底地震仪的位置校正[J].地球物理学报,2010,53(12):2982-2991.
[10]卫小冬,赵明辉,阮爱国,等.南海中北部OBS2006-3地震剖面中横波的识别与应用[J].热带海洋学报,2010,29(5):72-80.
[11]阮爱国,丘学林,李家彪,等.中国海洋深地震探测与研究进展[J].华南地震,2009,29(2):10-18.
[12]王泽中.海洋学研究的新知——深海底流沉积[J].大自然探索,1997,16(3):86-89.
[13]QIU XL,CHEN Y,ZHU RX,et a1.The application of largevolume airgun sources to the onshore-offshore seismicsurveys:Implication from the experimental results innorthern South China Sea[J].Chinese Science Bulletin,2007,52(4):553-560.
[14]赵明辉,丘学林,夏少红,等.大容量气枪震源及其波形特征[J].地球物理学报,2008,51(2):558-565.
[15]CHANG E T Y,HSU S K,LEE C S.Earthquake swarmrecorded by an ocean bottom seismic array in southwestoffshore of Taiwan in October,2005[J].Terr Atmos Ocean Sci,2008,19:717-728,doi:10.3319/TAO.2008.19.6.717(PT).
[16]游庆瑜,刘福田,冉崇荣,等.高频微功耗海底地震仪研制[J].地球物理学进展,2003,18(1):173-176.
[17]王嘹亮,张志荣,阎贫,等.潮汕坳陷地壳结构探测初步成果[J].南海地质研究,2004,15:62-67.
[18]游庆瑜,刘福田,冉崇荣.MCI微功耗宽频带数字地震仪[J].地球物理学报,2003,46(3):347-354.
[19]罗文造,阎贫,温宁,等.南海北部潮汕坳陷海区海底地震仪调查实验[J].热带海洋学报,2009,28(4):59-65.
[20]BROCHER T M,PARSONS T,CREAGER K C,et al.Wide-angle seismic recordings from the 1998 SeismicHazards Investigation of Puget Sound(SHIPS),WesternWashington and British Columbia[R]//U.S.GeologicalSurvey Open-File Report,1999:129-314.
[21]TODA SHINJI,LIN JIAN,STEIN R S.Using the 2011M=9.0 Tohoku earthquake to test the Coulomb stresstriggering hypothesis and to calculate faults brought closer tofailure[J].Earth Planets and Space,2011,(63):725-730.
[22]邹立晔.地震震相分析与测量的进展[J].国际地震动态,2004,(10):1-8.
[23]STORCHAK D A,SCHWEITZER J,BORMANN P.TheIASPEI standard seismic phase list[J].SeismologicalResearch Letters,2003,74(6):791-772.
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