南海北部海陆过渡带地壳平均速度及莫霍面深度分析
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摘要
南海北部海陆过渡带是一条深地震探测的空白带,其地壳结构研究不仅可以揭示华南沿海地区地震活动规律和构造活动特征,而且可以将以往在海上和陆上使用深地震探测所获得的地壳结构模型进行有效的衔接。鉴于南海北部海陆过渡带地壳结构的重要性,2004年我们在香港外海域进行了一次海陆地震联测实验。本文以此次实验中广东和香港地区固定地震台网以及担杆岛流动台所获得的数据为基础,对各台站接收到的Pg和PmP震相进行了近似横向均一的二维结构模拟,获得了各台站对应的地壳平均速度和PmP反射点处的莫霍面深度值。其结果显示研究区地壳平均速度普遍为6.2km·s-1左右,比全球地壳平均速度6.45km·s-1要低,这可能与普遍发育于华南沿海地带的中地壳低速层有关。研究区东边的SHW台所获得的地壳平均速度为6.7km·s-1左右,要明显高于全球地壳平均速度,它可能是由于局部异常结构所造成的,其与地幔岩浆的侵入作用可能存在一定联系。研究区莫霍面深度在26—35km左右,变化趋势较为明显,从北西向南东方向逐渐变浅,属于地壳减薄型结构,推测其可能与南海北部边缘的形成演化有密切联系。研究表明南海北部海陆过渡带是一个明显的转换地带,它的深部地壳结构特征应该与南海的扩张演化有密切联系,这些认识推进了华南地区和南海北部陆缘地壳结构和构造属性的深入研究。
In order to study the crustal structure beneath the onshore-offshore transitional zone in the northern South China Sea,we carried out an onshore-offshore seismic experiment offshore of Hong Kong in 2004.Based on the data recorded by the permanent seismic stations in Guangdong Province and Hong Kong and by portable seismic stations on the Dangan Islands,we obtained a series of laterally homogeneous 2-D models using Pg and PmP phases for every station,determined the crustal average velocity,and constrained variations of Moho depth.The results show that the crustal average velocity is generally about 6.2km·s-1,which is lower than the global crustal average velocity of 6.45km·s-1.It suggests that a low velocity layer in the middle crust has developed the beneath onshore-offshore transitional zone in the northern South China Sea.However,the av-erage crustal velocity of 6.7km·s-1 in the eastern part of the study area was higher than the global average velocity(6.45km·s-1) according to the data at the SHW station,which could imply magma underplating and a high velocity layer in the lower crust.The Moho depth was about 26-35km and gradually thinned from northwest to southeast.These results indicate the onshore-offshore transitional zone is the transitional boundary between the northern South China Sea and South China.By modeling and analyzing these data,we have obtained some new knowledge: a low velocity layer of middle crust was generally detected and no high velocity body of lower crust was found on land,while the opposite occurred at sea,namely high velocity body of lower crust was detected and no low velocity layer of middle crust was found;and the thickness of crust thinned from land to sea.These results have improved our understanding on crustal structure and tectonics of South China and the northern South China Sea.
In order to study the crustal structure beneath the onshore-offshore transitional zone in the northern South China Sea,we carried out an onshore-offshore seismic experiment offshore of Hong Kong in 2004.Based on the data recorded by the permanent seismic stations in Guangdong Province and Hong Kong and by portable seismic stations on the Dangan Islands,we obtained a series of laterally homogeneous 2-D models using Pg and PmP phases for every station,determined the crustal average velocity,and constrained variations of Moho depth.The results show that the crustal average velocity is generally about 6.2km·s-1,which is lower than the global crustal average velocity of 6.45km·s-1.It suggests that a low velocity layer in the middle crust has developed the beneath onshore-offshore transitional zone in the northern South China Sea.However,the av-erage crustal velocity of 6.7km·s-1 in the eastern part of the study area was higher than the global average velocity(6.45km·s-1) according to the data at the SHW station,which could imply magma underplating and a high velocity layer in the lower crust.The Moho depth was about 26-35km and gradually thinned from northwest to southeast.These results indicate the onshore-offshore transitional zone is the transitional boundary between the northern South China Sea and South China.By modeling and analyzing these data,we have obtained some new knowledge: a low velocity layer of middle crust was generally detected and no high velocity body of lower crust was found on land,while the opposite occurred at sea,namely high velocity body of lower crust was detected and no low velocity layer of middle crust was found;and the thickness of crust thinned from land to sea.These results have improved our understanding on crustal structure and tectonics of South China and the northern South China Sea.
引文
[1]姚伯初,曾维军,HAYES D E,等著.中美合作调研南海地质专报[M].北京:中国地质大学出版社,1994:1-203.
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[3]QIU X L,YE S Y,WU S M,et al.Crustal structure across the Xisha Trough,northwestern South China Sea[J].Tec-tonophysics,2001,341:179-193.
[4]YAN P,ZHOU D,LIU Z.A crustal structure profile across the northern continental margin of the South China Sea[J].Tectonophysics,2001,338:1-21.
[5]WANG T K,CHEN M K,LEE C S,et al.Seismic imaging of the transitional crust across the northeastern margin of the South China Sea[J].Tectonophysics,2006,412:237-254.
[6]吴振利,阮爱国,李家彪,等.南海中北部地壳深部结构探测新进展[J].华南地震,2008,28(1):21-28.
[7]廖其林,王振明,王屏路,等.福州—泉州—汕头地区地壳结构的爆炸地震研究[J].地球物理学报,1988,31(3):270-280.
[8]尹周勋,赖明惠,熊绍柏,等.华南连县—博罗—港口地带地壳结构及速度分布的爆炸地震探测结果[J].地球物理学报,1999,42(3):383-392.
[9]嘉世旭,李志雄,徐朝繁,等.雷琼拗陷地壳结构特征[J].地球物理学报,2006,49(5):1385-1394.
[10]郝天珧,刘建华,宋海斌,等.华南及其相邻边缘海域一些重要断裂的地球物理证据[J].地球物理学进展,2002,17(1):13-23.
[11]吴世敏,周蒂,丘学林.南海北部陆缘的构造属性问题[J].高校地质学报,2001,7(4):419-426.
[12]丘学林,施小斌,阎贫,等.南海北部地壳结构的深地震探测和研究新进展[J].自然科学进展,2003,13(3):231-236.
[13]HAYES D E,NISSEN S S.The South China Sea margings:Implications for rifting contrasts[J].Earth and Planetary Science Letters,2005,237:601-616.
[14]丘学林,陈,朱日祥,等.大容量气枪震源在海陆联测中的应用:南海北部试验结果分析[J].科学通报,2007,54(2):463-469.
[15]陈恩民,黄咏茵.华南十九次强震暨南海北部陆缘地震带概述[J].华南地震,1984,4(1):11-32.
[16]刘以宣.华南沿海的活动断裂[J].海洋地质与第四纪地质,1985,5(3):11-21.
[17]徐杰,张进,周本刚,等.关于南海北部滨海断裂带的研
[18]钟建强.滨海断裂带之所在及其活动性初探[J].华南地震,1987,7(4):1-7.
[19]赵明辉,丘学林,夏戡原,等.南海东北部滨海断裂带的研究现状与展望[J].华南地震,2003,23(1):20-27.
[20]夏少红,丘学林,赵明辉,等.香港与珠三角地区海陆联合地震探测的数据处理[J].热带海洋学报,2007,26(1):35-38.
[21]赵明辉,丘学林,夏戡原,等.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,2004,23(1):58-63.
[22]COHEN J K,STOCKWELL J W.The SU user’s manual[M].Colorado School of Mines,1995:1-40.
[23]ZELT C A,SMITH R B.Seismic traveltime inversion for 2-D crustal velocity structure[J].Geophys J Int,1992,108:16-34.
[24]LI H,MOROZOV I B,SMITHSON S B.3D seismic analy-sis of the Coast Shear Zone in SE Alaska and Western British Columbia:Broadside analysis of ACCRETE wide-angle data[J].Tectonophysics,2008,448:20-32.
[25]XIA S H,ZHAO M H,QIU X L,et al.Crustal structure in an onshore-offshore transitional zone near Hong Kong,northern South China Sea[J].Journal of Asian Earth Sciences,2010,37:460-472.
[26]赵明辉,丘学林,叶春明,等.南海东北部海陆联测与滨海断裂带两侧地壳结构分析[J].地球物理学报,2004,47(5):845-852.
[27]ZHANG Z,WANG Y.Crustal structure and contact relation-ship revealed from deep seismic sounding data in South China[J].Phys Earth Planet Interiors,2007,165:114-126.
[28]蔡学林,朱介寿,曹家敏,等.中国大陆及邻区岩石圈地壳三维结构与动力学型式[J].中国地质,2007,34(4):543-557.
[29]CHRISTENSEN N I,MOONEY W D.Seismic velocity structure and composition of the continental crust:A global view[J].J Geophys Res,1995,101:9761-9788.
[30]赵明辉,丘学林,徐辉龙,等.南海北部沉积层和地壳内低速层的分布和识别[J].自然科学进展,2007,17(4):471-479.
[31]夏少红,丘学林,赵明辉,等.香港地区海陆地震联测及深部地壳结构研究[J].地球物理学进展,2008,23(5):1389-1397.
[32]丘学林,赵明辉,叶春明,等.南海东北部海陆联测与海底地震仪探测[J].大地构造与成矿学,2003,27(4):究[J].华南地震,2006,26(4):8-13.295-300.
[2]NISSEN S S,HAYES D E,YAO B,et al.Gravity,heat flow,and seismic constrains on the process of crustal extension:Northern margin of the South China Sea[J].Journal of Geo-physical Research,1995,100(B11):22447-22483.
[3]QIU X L,YE S Y,WU S M,et al.Crustal structure across the Xisha Trough,northwestern South China Sea[J].Tec-tonophysics,2001,341:179-193.
[4]YAN P,ZHOU D,LIU Z.A crustal structure profile across the northern continental margin of the South China Sea[J].Tectonophysics,2001,338:1-21.
[5]WANG T K,CHEN M K,LEE C S,et al.Seismic imaging of the transitional crust across the northeastern margin of the South China Sea[J].Tectonophysics,2006,412:237-254.
[6]吴振利,阮爱国,李家彪,等.南海中北部地壳深部结构探测新进展[J].华南地震,2008,28(1):21-28.
[7]廖其林,王振明,王屏路,等.福州—泉州—汕头地区地壳结构的爆炸地震研究[J].地球物理学报,1988,31(3):270-280.
[8]尹周勋,赖明惠,熊绍柏,等.华南连县—博罗—港口地带地壳结构及速度分布的爆炸地震探测结果[J].地球物理学报,1999,42(3):383-392.
[9]嘉世旭,李志雄,徐朝繁,等.雷琼拗陷地壳结构特征[J].地球物理学报,2006,49(5):1385-1394.
[10]郝天珧,刘建华,宋海斌,等.华南及其相邻边缘海域一些重要断裂的地球物理证据[J].地球物理学进展,2002,17(1):13-23.
[11]吴世敏,周蒂,丘学林.南海北部陆缘的构造属性问题[J].高校地质学报,2001,7(4):419-426.
[12]丘学林,施小斌,阎贫,等.南海北部地壳结构的深地震探测和研究新进展[J].自然科学进展,2003,13(3):231-236.
[13]HAYES D E,NISSEN S S.The South China Sea margings:Implications for rifting contrasts[J].Earth and Planetary Science Letters,2005,237:601-616.
[14]丘学林,陈,朱日祥,等.大容量气枪震源在海陆联测中的应用:南海北部试验结果分析[J].科学通报,2007,54(2):463-469.
[15]陈恩民,黄咏茵.华南十九次强震暨南海北部陆缘地震带概述[J].华南地震,1984,4(1):11-32.
[16]刘以宣.华南沿海的活动断裂[J].海洋地质与第四纪地质,1985,5(3):11-21.
[17]徐杰,张进,周本刚,等.关于南海北部滨海断裂带的研
[18]钟建强.滨海断裂带之所在及其活动性初探[J].华南地震,1987,7(4):1-7.
[19]赵明辉,丘学林,夏戡原,等.南海东北部滨海断裂带的研究现状与展望[J].华南地震,2003,23(1):20-27.
[20]夏少红,丘学林,赵明辉,等.香港与珠三角地区海陆联合地震探测的数据处理[J].热带海洋学报,2007,26(1):35-38.
[21]赵明辉,丘学林,夏戡原,等.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,2004,23(1):58-63.
[22]COHEN J K,STOCKWELL J W.The SU user’s manual[M].Colorado School of Mines,1995:1-40.
[23]ZELT C A,SMITH R B.Seismic traveltime inversion for 2-D crustal velocity structure[J].Geophys J Int,1992,108:16-34.
[24]LI H,MOROZOV I B,SMITHSON S B.3D seismic analy-sis of the Coast Shear Zone in SE Alaska and Western British Columbia:Broadside analysis of ACCRETE wide-angle data[J].Tectonophysics,2008,448:20-32.
[25]XIA S H,ZHAO M H,QIU X L,et al.Crustal structure in an onshore-offshore transitional zone near Hong Kong,northern South China Sea[J].Journal of Asian Earth Sciences,2010,37:460-472.
[26]赵明辉,丘学林,叶春明,等.南海东北部海陆联测与滨海断裂带两侧地壳结构分析[J].地球物理学报,2004,47(5):845-852.
[27]ZHANG Z,WANG Y.Crustal structure and contact relation-ship revealed from deep seismic sounding data in South China[J].Phys Earth Planet Interiors,2007,165:114-126.
[28]蔡学林,朱介寿,曹家敏,等.中国大陆及邻区岩石圈地壳三维结构与动力学型式[J].中国地质,2007,34(4):543-557.
[29]CHRISTENSEN N I,MOONEY W D.Seismic velocity structure and composition of the continental crust:A global view[J].J Geophys Res,1995,101:9761-9788.
[30]赵明辉,丘学林,徐辉龙,等.南海北部沉积层和地壳内低速层的分布和识别[J].自然科学进展,2007,17(4):471-479.
[31]夏少红,丘学林,赵明辉,等.香港地区海陆地震联测及深部地壳结构研究[J].地球物理学进展,2008,23(5):1389-1397.
[32]丘学林,赵明辉,叶春明,等.南海东北部海陆联测与海底地震仪探测[J].大地构造与成矿学,2003,27(4):究[J].华南地震,2006,26(4):8-13.295-300.
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