南海西沙地块岛屿地震观测和海陆联测初步结果
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摘要
为了研究南海西沙地块下方的地壳结构,我们在岛屿区架设了流动地震台站进行天然地震观测和海底地震仪的人工地震探测.本文利用远震接收函数方法和射线追踪方法对琛航台的远震数据和海陆联测数据进行了初步处理和分析,建立了琛航岛下方的一维横波速度模型以及横穿琛航岛的二维地壳结构模型.琛航岛顶部存在2 km厚的新生代低速沉积层,下地壳存在明显低速层,横波速度只有3.5 km/s,莫霍面埋深24～26 km,岛屿两侧地壳厚度向外逐渐变薄,其西北侧地壳结构表现为裂谷特征,可能为西沙海槽在该地区的延伸表现.地幔热活动和区域拉张应力作用引起的上地幔物质的韧性流变构造和各向异性排列可能是产生下地壳低速层的主要原因.
Temporary earthquake stations were installed on islands of Xisha Block and onshore-offshore deep seismic experiment was carried out in order to study the crustal structure beneath Xisha Block.The seismic data were analyzed and processed.A 1-D shear wave velocity model beneath Chenhang island(CHH) was constructed by applying receiver function method to the teleseismic data.A 2-D P-wave velocity crustal structure was modeled by ray-tracing and travel-time simulation.A 2 km-thick low-velocity sediment exists on the top of CHH which is attributed to Cenozoic deposition.In the lower crust,there exists a prominent Low-Velocity Layer(LVD with average shear wave velocity of 3.5 km/s;Moho interface lies at the depth of 24～26 km right beneath CHH.The crustal thickness gradually decreases outward along the onshore-offshore seismic line.The crustal structure has the typical characteristics of rift valley in the NW side of CHH.which belongs to the extension of Xisha Trough.The presence of anisotropy of upper mantle minerals and the ductile rheological structure arising from hot mantle activities may result in the generation of the LVL in lower crust.
Temporary earthquake stations were installed on islands of Xisha Block and onshore-offshore deep seismic experiment was carried out in order to study the crustal structure beneath Xisha Block.The seismic data were analyzed and processed.A 1-D shear wave velocity model beneath Chenhang island(CHH) was constructed by applying receiver function method to the teleseismic data.A 2-D P-wave velocity crustal structure was modeled by ray-tracing and travel-time simulation.A 2 km-thick low-velocity sediment exists on the top of CHH which is attributed to Cenozoic deposition.In the lower crust,there exists a prominent Low-Velocity Layer(LVD with average shear wave velocity of 3.5 km/s;Moho interface lies at the depth of 24～26 km right beneath CHH.The crustal thickness gradually decreases outward along the onshore-offshore seismic line.The crustal structure has the typical characteristics of rift valley in the NW side of CHH.which belongs to the extension of Xisha Trough.The presence of anisotropy of upper mantle minerals and the ductile rheological structure arising from hot mantle activities may result in the generation of the LVL in lower crust.
引文
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[12]赵明辉,丘学林,叶春明等.南海东北部海陆深地震联测与滨海断裂带两侧地壳结构分析.地球物理学报,2004,47 (5):845-852 Zhao M H,Qiu X L,Ye C M,et al.Analysis on deep crustal structure along the onshore-offshore seismic profile across the Binhai(Littoral) Fault Zone in northeastern South China Sea.Chinese J.Geophys.(in Chinese),2004,47(5):845- 852
[13]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.Journal of Asian Earth Sciences,2010,37 (5-6):460-472
[14]Okaya D,Henrys S,Stern T.Double-sided onshore-offshore seismic imaging of a plate boundary:"super-gathers" across South Island,New Zealand.Tectonophysics,2002,355(1-4):247-263
[15]黄海波,丘学林,胥颐等.利用远震接收函数方法研究南海西沙群岛下方地壳结构.地球物理学报,2011,54(11): 2788-2798 Huang H B,Qiu X L,Xu Y,et al.Crustal structure beneath the Xisha Islands of the South China Sea simulated by the teleseismic receiver function method.Chinese J.Geophys. (in Chinese),2011,54(11):2788-2798
[16]Leahy G M,Park J.Hunting for oceanic island Moho. Geophysical Journal International,2005,160(3):1020-1026
[17]丘学林,曾钢平,胥颐等.南海西沙石岛地震台下的地壳结构研究.地球物理学报,2006,49(6):1720-1 729 Qiu X L,Zeng G P,XuY,et al.The crustalstructure beneath the Shidao Station on Xisha Islands of South China Sea.Chinese J.Geophys.(in Chinese),2006,49(6):1720- 1729
[18]阮爱国,李家彪,郝天姚等.石岛地震台远震记录反演研究.海洋学报,2006,28(2):85-91 Ruan A G,Li J B,Hao T Y,et al.Inversion of far-field seismic waves at Shidao Seismographic Station.Acta Oceanologica Sinica(in Chinese),2006,28(2):85-91
[19]Cassidy J F.Numerical experiments in broadband receiver function analysis.Bulletin of the Seismological Society of America,1992,82(3):1453-1474
[20]游庆瑜,刘福田,冉崇荣等.高频微功耗海底地震仪研制.地球物理学进展,2003,18(1):1 73-176 You Q Y,Liu F T,Ran C R,et al.High frequency micropower ocean bottom seismograph.Progress in Geophysics(in Chinese),2003,18(1):173-176
[21]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.地球物理学报,2010,53(4):1015-1018 Ruan AG,Li J B,Chen Y S,et al.The experiment of broad band I-4C type OBS in the Southwest India ridge.Chinese J. Geophys.(in Chinese),2010,53(4):1015-1018
[22]伍忠良.海洋天然气水合物三维地震与海底地震勘探中的震源技术研究.热带海洋学报,2011,30(1):49-60 Wu Z L.Study of source in 3-D seismic and OBS exploration for marine gas hydrate.Journal of Tropical Oceanography (in Chinese),2011,30(1):49-60
[23]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.地球物理学报,2010,53 (12):2982-2991 Ao W,Zhao M H,Qiu X L,et al.The correction of shot and OBS position in the 3D seismic experiment of the SW Indian Ocean Ridge.Chinese J.Geophys.(in Chinese), 2010,53(12):2982-2991
[24]Zelt C A,Smith R B.Seismic traveltime inversion for 2-D crustal velocity structure.Geophysics Journal International, 1992,108(1):16-34
[25]黄海波,夏少红.丘学林等.海陆地震联测:相邻地震台站的信号及震相特征对比.热带海洋学报,2010,29(6):153- 161 Huang H B,Xia S H,Qiu X L,et al.Onshore-offshore seismic experiment;signal characteristics and seismic phases received by two adjacentseismic stations.Journal of Tropical Oceanography(in Chinese),2010,29(6):153- 161
[26]赵明辉,丘学林,夏少红等.大容量气枪震源及其波形特征.地球物理学报,2008,51(2):558-565 Zhao M H,Qiu X L,Xia S H,et al.Large volume air-gun sources and its seismic waveform characters.Chinese J. Geophys.(in Chinese),2008,51(2):558-565
[27]Zhao M,Qiu X,Xia S,et al.Seismic strucutre in the northeastern South China Sea:S-wave velocity and V_p/V_s ratios derived from three-component OBS data.Tectonophysics, 2010,480:183-197
[2]Qiu X L,Chen Y,Zhu R X,et al.The application of large volume airgun sources to the onshore-offshore seismic surveys:implication of the experimental results in northern South China Sea.Chinese Science Bulletin,2007,52(4): 553-560
[3]Qiu X L,Ye S Y,Wu S M,et al.Crustal structure across the Xisha Trough,northwestern South China Sea.Tectonophysics, 2001,341(1-4):179-193
[4]敖威.南海西北部OBS2006-2测线深部地壳结构研究[硕士论文].北京:中国科学院研究生院,2011 Ao W.Crustal structure of the northwestern South China Sea:Wide-angle reflection/refraction data of OBS2006-2(in Chinese)[Master s thesis].Beijing:Graduate School of the Chinese Academy of Sciences,2011
[5]Ammon C J,Randall G E,Zandt G.On the nonuniqueness of receiver function inversions.Journal of Geophysical Research, 1990,95(B10):15303-15318
[6]Langston C A.Structure under Mount Rainier,Washington, inferred from teleseismic body waves.Journal of Geophysical Research,1979,84(B9):4749-4762
[7]吴庆举,曾融生.用宽频带远震接收函数研究青藏高原的地壳结构.地球物理学报,1998,41(5):669-679 Wu Q J,Zeng R S.The crustal structure of Qinghai-Xizang plateau inferred from broadband teleseismic waveform. Chinese J.Geophys.(Acta Geophysica Sinica)(in Chinese), 1998,41(5):669-679
[8]刘启元,Rainer K,李顺成.中国数字地震台网的接收函数及其非线性反演.地球物理学报,1 997,40(3):356-368 Liu Q Y,Rainer K,Li S C.Receiver functions at the stations of the Chinese Digital Seismic Network(CDSN) and their nonlinear inversion.Chinese J.Geophys.(Acta Geophysica Sinica)(in Chinese),1997,40(3):356-368
[9]Yuan X,Sobolev S V,Kind R,et al.Subduction and collision processes in the Central Andes constrained by converted seismic phases.Nature,2000,408(6815):958- 961
[10]Qiu X L,Priestley K,McKenzie D.Teleseismic P-waveform receiver function analysis and its application to Qiongzhong station(QIZ) of Hainan Island,NW South China Sea. Journal of Geosciences of China,2002,4(1):1-8
[11]胥颐,刘建华,傅竹武等.西沙群岛和哀牢山—红河地区的宽频带地震观测.热带海洋学报,2003,22(2):83-88 Xu Y,Liu J H,Fu Z W,et al.Broadband earthquake observation in Xisha Islands and Ailao Shan-Red River region.Journal of Tropical Oceanography(in Chinese), 2003,22(2):83-88
[12]赵明辉,丘学林,叶春明等.南海东北部海陆深地震联测与滨海断裂带两侧地壳结构分析.地球物理学报,2004,47 (5):845-852 Zhao M H,Qiu X L,Ye C M,et al.Analysis on deep crustal structure along the onshore-offshore seismic profile across the Binhai(Littoral) Fault Zone in northeastern South China Sea.Chinese J.Geophys.(in Chinese),2004,47(5):845- 852
[13]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.Journal of Asian Earth Sciences,2010,37 (5-6):460-472
[14]Okaya D,Henrys S,Stern T.Double-sided onshore-offshore seismic imaging of a plate boundary:"super-gathers" across South Island,New Zealand.Tectonophysics,2002,355(1-4):247-263
[15]黄海波,丘学林,胥颐等.利用远震接收函数方法研究南海西沙群岛下方地壳结构.地球物理学报,2011,54(11): 2788-2798 Huang H B,Qiu X L,Xu Y,et al.Crustal structure beneath the Xisha Islands of the South China Sea simulated by the teleseismic receiver function method.Chinese J.Geophys. (in Chinese),2011,54(11):2788-2798
[16]Leahy G M,Park J.Hunting for oceanic island Moho. Geophysical Journal International,2005,160(3):1020-1026
[17]丘学林,曾钢平,胥颐等.南海西沙石岛地震台下的地壳结构研究.地球物理学报,2006,49(6):1720-1 729 Qiu X L,Zeng G P,XuY,et al.The crustalstructure beneath the Shidao Station on Xisha Islands of South China Sea.Chinese J.Geophys.(in Chinese),2006,49(6):1720- 1729
[18]阮爱国,李家彪,郝天姚等.石岛地震台远震记录反演研究.海洋学报,2006,28(2):85-91 Ruan A G,Li J B,Hao T Y,et al.Inversion of far-field seismic waves at Shidao Seismographic Station.Acta Oceanologica Sinica(in Chinese),2006,28(2):85-91
[19]Cassidy J F.Numerical experiments in broadband receiver function analysis.Bulletin of the Seismological Society of America,1992,82(3):1453-1474
[20]游庆瑜,刘福田,冉崇荣等.高频微功耗海底地震仪研制.地球物理学进展,2003,18(1):1 73-176 You Q Y,Liu F T,Ran C R,et al.High frequency micropower ocean bottom seismograph.Progress in Geophysics(in Chinese),2003,18(1):173-176
[21]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.地球物理学报,2010,53(4):1015-1018 Ruan AG,Li J B,Chen Y S,et al.The experiment of broad band I-4C type OBS in the Southwest India ridge.Chinese J. Geophys.(in Chinese),2010,53(4):1015-1018
[22]伍忠良.海洋天然气水合物三维地震与海底地震勘探中的震源技术研究.热带海洋学报,2011,30(1):49-60 Wu Z L.Study of source in 3-D seismic and OBS exploration for marine gas hydrate.Journal of Tropical Oceanography (in Chinese),2011,30(1):49-60
[23]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.地球物理学报,2010,53 (12):2982-2991 Ao W,Zhao M H,Qiu X L,et al.The correction of shot and OBS position in the 3D seismic experiment of the SW Indian Ocean Ridge.Chinese J.Geophys.(in Chinese), 2010,53(12):2982-2991
[24]Zelt C A,Smith R B.Seismic traveltime inversion for 2-D crustal velocity structure.Geophysics Journal International, 1992,108(1):16-34
[25]黄海波,夏少红.丘学林等.海陆地震联测:相邻地震台站的信号及震相特征对比.热带海洋学报,2010,29(6):153- 161 Huang H B,Xia S H,Qiu X L,et al.Onshore-offshore seismic experiment;signal characteristics and seismic phases received by two adjacentseismic stations.Journal of Tropical Oceanography(in Chinese),2010,29(6):153- 161
[26]赵明辉,丘学林,夏少红等.大容量气枪震源及其波形特征.地球物理学报,2008,51(2):558-565 Zhao M H,Qiu X L,Xia S H,et al.Large volume air-gun sources and its seismic waveform characters.Chinese J. Geophys.(in Chinese),2008,51(2):558-565
[27]Zhao M,Qiu X,Xia S,et al.Seismic strucutre in the northeastern South China Sea:S-wave velocity and V_p/V_s ratios derived from three-component OBS data.Tectonophysics, 2010,480:183-197
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