珠江口外伶仃洋海底含气沉积物声波反射及衰减特征
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摘要
高分辨率地震剖面显示,在珠江口外伶仃洋海底有大面积含气沉积物。根据含气沉积物地震反射特征将其分为声学空白、声学幕、声学扰动、不规则强反射顶部和相位下拉等类型。对含气沉积物声波衰减初步分析表明约在3.3 kHz附近有一衰减峰值,将实际资料与理论模型计算进行对比,认为此峰值频率对应于等效半径约6 mm的气泡的特征振荡频率,此等效半径气泡的阻尼振荡是引起声波衰减的主要原因。
High-resolution seismic profiles indicate that there is a large area of seafloor gas-containing sediment in the outer Lingding Bay of the Zhujiang Estuary.According to the seismic reflection characteristics of gas-containing sediment,the seismic features of shallow gas are divided into five types: an acoustic blanket,an acoustic curtain,acoustic turbidity,an irregular strong top reflection boundary,and a reflection phase pull-down.The acoustic attenuation of gas-containing sediment is primarily analyzed.The result indicates that there is an attenuation peak near the frequency of 3.3 kHz.According to the comparison between surveying data and model results,it is demonstrated that the attenuation peak frequency corresponds to the fundamental resonance frequency of bubbles with 6 mm equivalent radium.The primary conclusion is drawn that the acoustic attenuation is mainly caused by the damping resonance of bubbles with the 6 mm equivalent radium.
High-resolution seismic profiles indicate that there is a large area of seafloor gas-containing sediment in the outer Lingding Bay of the Zhujiang Estuary.According to the seismic reflection characteristics of gas-containing sediment,the seismic features of shallow gas are divided into five types: an acoustic blanket,an acoustic curtain,acoustic turbidity,an irregular strong top reflection boundary,and a reflection phase pull-down.The acoustic attenuation of gas-containing sediment is primarily analyzed.The result indicates that there is an attenuation peak near the frequency of 3.3 kHz.According to the comparison between surveying data and model results,it is demonstrated that the attenuation peak frequency corresponds to the fundamental resonance frequency of bubbles with 6 mm equivalent radium.The primary conclusion is drawn that the acoustic attenuation is mainly caused by the damping resonance of bubbles with the 6 mm equivalent radium.
引文
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[2]ANDERSON A L,HAMPTON L D.Acoustics of gas-bearing sediments:Ⅰ.Background[J].J Acoust Soc Am,1980,67(6):1865—1889.
[3]ANDERSON A L,HAMPTON L D.Acoustics of gas-baring sediments:Ⅱ.Measurements and model[J].J Acoust Soc Am,1980,67(6):1865—1889.
[4]SCULER F.Undersuchungen ulber die Machtigkeit von Schlickschichtem mit Hilfe des Echographen[J].Dt Hydrographiche Zeitung,1952,5:220—231.
[5]FADER G B J.Gas-related sedimentary features from the eastern Canadian continental shelf[J].Cont Shelf Res,1991,11:1123—1153.
[6]ISMAIL K,MAKOTO O,HIROMI M S,et al.Seafloor gas seeps and sediment failures triggered by the August 17,1999 earthquake inthe eastern part of the Gulf of Izmit,Sea of Marmara,NW Turkey[J].Marine Geology,2005,215:193—214.
[7]MISSIAEN T,MURPHY S,LONCKE L,et al.Very high-resolution seismic mapping of shallow gas in the Belgian coastal zone[J].Cont Shelf Res,2002,22:2291—2301.
[8]ANNA C,ANTONIO S,GIAN M,et al.Gas seeps and rock formation in the northern Adriatic Sea[J].Cont Shelf Res,2002,22:2333—2344.
[9]TAYLOR D I.Nearshore shallow gas around the U K coast[J].Cont Shelf Res,1992,12:1135—1144.
[10]WILKENS R H,RICHARDSON M D.The influence of gas on sediment acoustic properties:in situ,laboratory,and theoretical resultsfrom Eckernforde Bay,Balti Sea[J].Cont Shelf Res,1998,18:1859—1892.
[11]ANDERSON A L,ABEGG F,HAWKINS J A,et al.Bubble populations and acoustic interaction with the gassy floor of EckernfordeBay[J].Cont Shelf Res,1998,18:1807—1838.
[12]GORGASA T J,KIMB G Y,PARKC S C.Evidence for gassy sediments on the inner shelf of SE Korea from geoacoustic properties[J].Cont Shelf Res,2003,23:821—834.
[13]周良勇,刘健,刘锡清,等.现代黄河三角洲滨浅海区的灾害地质[J].海洋地质与第四纪地质,2004,24(3):19—27.
[14]项培林,成利民,王如金,等.浙江省三北浅滩浅层天然气地质灾害[J].中国地质灾害与防治学报,2005,16(2):38—42.
[15]鲍才旺,姜玉坤.中国近海海底潜在地质灾害类型及特征[J].热带海洋,1999,18(3):24—31.
[16]杨木壮,梁修权,王宏斌,等.南海北部湾海洋工程地质特征[J].海洋地质与第四纪地质,2000,20(4):47—52.
[17]顾兆峰,张志,刘怀山,等.南黄海西部地区浅层气地震特征[J].海洋地质与第四纪地质,2006,26(3):65—74.
[18]李官保,刘保华,吴金龙,等.伶仃洋南部断裂构造特征[J].海洋科学进展,2006,24(3):320—328.
[19]COURTNEY R C,MAYER L A.Calculation of acoustic parameters by a filter-correlation method[J].J Acoust Soc Am,1993,93(2):1145—1154.
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