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1 热带海洋学报 JOURNAL OF TROPICAL OCEANOGRAPHY 海洋地球物理学 doi: / 年第 35 卷第 5 期 : 75 * 陈金虎 1,2, 夏少红 1, 曹敬贺 1, 万奎元 1,2, 丘学林 1.,, , : (ocean bottom seismometer, OBS), /,, OBS, Tomo2D,, OBS, ( 4km), ( 2km), ;,, ;, ; 10km, 5km, 3km, 20km 30km 10km 3km : (OBS); ; ; ; 中图分类号 : P738.4 文献标识码 : A 文章编号 : (2016) Analysis on uncertainty in velocity structure inversion in wide-angle seismic experiments CHEN Jinhu 1,2, XIA Shaohong 1, CAO Jinghe 1, WAN Kuiyuan 1,2, QIU Xuelin 1 1. Key Laboratory of Marginal Sea Geology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou , China 2. University of Chinese Academy of Sciences, Beijing , China Abstract: Ocean bottom seismometer (OBS) wide-angle seismic exploration is an important geophysical method to obtain elaborate crust-mantle structure of deep sea. The main theory is to invert the deep crustal structure by refraction and reflection seismic phase and to provide basal seismic information for studying crust structural features. Based on the principle of seismic tomography structure inversion, we aimed at the uncertainty of velocity structure inversion in OBS wide-angle seismic experiment in this study. Several synthetic models and data were built by Tomo2D to study issues such as how different sedimentary layers may influence the inversion result of whole crust velocity structure, how the OBS space may influence the resolving accuracy of high velocity layer (HVL) in lower crust and the effectiveness of identifying the deep crust anomalous 收稿日期 ; 修订日期 : 基金项目 ( ); 作者简介 (1989),,, jinhuchen@scsio.ac.cn * Received date: ; Revised date: Editor: SUN Shujie Foundation item: National Natural Science Foundation of China ( ); Program for Distinguished Young Scholars of Chinese Academy of Science Author: CHEN Jinhu. jinhuchen@scsio.ac.cn

2 76 Vol. 35, No. 5 / Sep., 2016 bodies. Our results show that the HVL thicker than 4 km can be well inverted and the thinner HVL (<2 km) is poorly inverted for its scale and shape. The deviation of sedimentary thickness in initial model can influence how to identify HVL; the larger deviation corresponds to worse identification. The low-velocity layer within the crust has significant impact on inverting the scale of HVL in lower crust, but the thickness of the low-velocity layer is insignificant. The smallest scale of velocity anomalous body that can be identified is 5 km in the horizontal and 3 km in the vertical when the OBS space is 10 km; and they are 10 km in the horizontal and 3 km in the vertical when the OBS space is 20 km and 30 km. Key words: ocean bottom seismometer; wide-angle seismic; high velocity layer; velocity structure inversion; South China Sea (ocean bottom seismometer, OBS) 30,,, OBS,, 100km, 200~300km, 30~40km, (, 2007),,, (, 2012), (, 2014), OBS, OBS OBS (, 2003;, 2010;, 2012), OBS,, OBS, OBS, OBS OBS 15~30km (, 2008;, 2010;, 2011;, 2011;, 2012) OBS /,,,,,, OBS,, Tomo2D,,,, OBS, 1 Tomo2D (Korenaga et al, 2000)/, (LSQR)(Korenaga et al, 2000;, 2014),, δt j Г j δu, : δt j δud (1) : j T δtj δud x x δzx j j (2) j z, x j j, z, (1)(2) : d=gδm (3) d, G, δm, C d, d,

3 : 77,,,, (3): 1/2 1/2 d m G C GC 1/2 m δm C δm (4) 1/2 = d d C d C m ( m model),, (3),,, : d Gv wgd δmv 0 vlhv v Vv 0 (5) L δmd 0 0 w w dld, G v d ; λ v λ d ; L Hv L Vv, L d ; δm v δm d ; w,,,, (5), LSQR,,, (5) : d Gv wgd 0 vlhv 0 δ v 0 v Vv 0 m L w L δm d d d 0 vdv 0 w 0 0 w ddd (6), D v D d ; α v α d Tomo2D 4 : 2 2 4,, (secant and bisection method),,,, : m i1 m i 1 L v δ m i δ m c (7) L v, δm i i, m i m i+1 i i+1 δm c, : c v Gm δ G L δm δm (8) (1)(8) Korenaga (2000) 2 20, OBS ( 1), (Nissen et al, 1995; Yan et al, 2001; Wang et al, 2006; Zhao et al, 2010;, 2011),, (Nissen et al, 1995;, 1998; Yan et al, 2001; Qiu et al, 2001;, 2008) ( 2), 1~5 km (Yan et al, 2001; Wang et al, 2006), 10km (Nissen et al, 1995;, 2011),,, 2.1,, i i

4 78 Vol. 35, No. 5 / Sep., OBS OBS Fig. 1 Distribution of wide-angle seismic exploration in the northern South China Sea 2 (Moho)(Nissen et al, 1995; Yan et al, 2001; Wang et al, 2006;, 2011) 1 Fig. 2 Distribution of high velocity layers and Moho from part of the deep seismic profiles in the northern South China sea (Nissen et al, 1995; Yan et al, 2001; Wang et al, 2006;, 2011). The profile's locations are marked by red lines in Fig. 1,, χ 2 1, PgPmP, : 1km, P 1.5kms 1 ; P 4 kms kms 1 ; 7.2 kms 1, 7.5 kms 1, 1km2km4km6km8km; 25km, P 8 kms 1, Tomo2D Pg PmP OBS, Pg PmP 10~60km 40~80km, 5 80~100s 250m, OBS 20km,

5 : 79,, 6.9 kms kms 1,, ( 3ae) 3 ae 1km2km4km6km8km ; fj ; OBS Fig. 3 Uncertainty test of the high velocity layer (HVL) in lower crust 2.2 (χ 2 ) 1 RMS, χ 2 RMS,,, ( 3fj) 3,,,

6 80 Vol. 35, No. 5 / Sep., 2016, 1km 2km,, ; 4km, ; 6km 8km 0, 1, χ 2 1, RMS 表 1 高速层不确定性测试反演参数值及结果统计 Tab. 1 Inversion parameter values and results of the uncertainty test of high velocity layer /km (L ht L hb L vt L vb L hr ) (D V D D S V S D ) χ 2 RMS/ms : 0, OBS 20km; L ht L hb L vt L vb L hr ; D V D D S V S D ( 3fj) 1km 2km ( 4),,,,, ( 0.05kms 1 ),,,, ( 5) 4 8km OBS Fig. 4 Rays density of inversed velocity structure model with 8 km HVL 5 ; 0.05kms 1 Fig. 5 Recovery level of the high velocity layer and the whole model 5,, : 1km, 0.05kms %; 6km 8km 77.42% 79.91%,,,, 3, OBS

7 : 81,,,, 3.1, : 1km, P 1.5kms 1 ; 4km, P 1.7 kms kms 1 ; 15km, P 5.2kms 1 6.9kms 1 ; 5km, 7.2kms 1 7.5kms 1 ; 25km, P 8.0kms 1 Pg PmP 10~60km 40~80km, OBS 20km, 250m, 0.0kms 1 0.1kms 1 0.3kms 1 ;, 20~25km P 6.9kms 1, P 7.0kms 1, 3.2,,, ( 6) 6 abc (); def (), OBS Fig. 6 Uncertainty test of the velocity structure of sedimentary layers 6, ( 6a), ( 6d); 0.1kms 1 ( 6b), ( 6e),, ; 0.3kms 1 ( 6c), ( 6f),,

8 82 Vol. 35, No. 5 / Sep., , χ , , RMS 10ms,,, 表 2 沉积层不确定性测试反演参数值及结果统计 Tab. 2 Inversion parameter values and results of the uncertainty test of sedimentary layers - /(kms 1 ) (L ht L hb L vt L vb L hr ) (D V D D S V S D ) χ 2 RMS/ms : OBS 20km, 0.05kms 1 ( 7), 7, 0.05kms 1, 0kms 1 0.3kms 1,, ; 0kms 1, 67.31% 95.21%78.47%; 0.1kms 1, 32.39%88.60%65.58%; 0.3kms 1, 0%15.22%32.11%,,,, (), 7 ; 0.05kms 1 Fig. 7 Recovery level of the high velocity layer, the sedimentary layer and the whole model 4,,, 4.1, 9~10km 8~11km8~13km, 6km,, 0.3kms 1 4.2,,, ( 8) 3, χ 2, RMS 10ms,,, 8 3d 3i :, ;, ( def),, ;,, 5 OBS

9 : 83 8 abc (); def (), OBS Fig. 8 Uncertainty test of the low velocity layers 表 3 低速层不确定性测试反演参数值及结果统计 Tab. 3 Inversion parameter values and results of the uncertainty test of low velocity layers /km (L ht L hb L vt L vb L hr ) (D V D D S V S D ) χ 2 RMS/ms : OBS 20km,, 10km20km30km,, OBS, : 4, 10km 5km ( 9a); 4, 10km 3km ( 9e) 30km20km10km,, ( 9bd 9fh) 9 bcd, 10km5km, : 30km,,,, ; 20km, 30km,,,

10 84 Vol. 35, No. 5 / Sep., a 10km5km, bcd 30km20km10km ; e 10km3km, fgh 30km20km10km ; OBS Fig. 9 Perturbation models in different OBS space of larger velocity anomalous body ; 10km,,,,, 10km3km,, 30km,,, ; 20km, 10km,, 10a, 5km 5km, OBS 30km20km10km ( 10bd), 5km5km, 30km 20km,, ; 10km,, 5km 3km ( 10e), 10km ( 10f), OBS,, OBS,

11 : a 5km5km, bcd 30km20km10km ; e 5km3km, f 10km ; OBS Fig. 10 Perturbation models in different OBS space of smaller velocity anomalous body, 20km,,, ;,, OBS,,,,,, OBS,, OBS,,, 6 Tomo2D OBS, OBS, : 1) : 2km, 20km, ;, 4km, Tomo2D

12 86 Vol. 35, No. 5 / Sep., 2016, 2),,, OBS 3), 4) OBS,,, ; 10km 10km 5km, 10km 3km, 5km 3km; 20km 10km 3km, ; 30km 10km 5km, 10km 3km, 20km,, OBS References,,,, [J]., 53(12): AO WEI, ZHAO MINGHUI, QIU XUELIN, et al, The correction of shot and OBS position in the 3D seismic experiment of the SW Indian Ocean Ridge[J]. Chinese Journal of Geophysics, 53(12): (in Chinese).,,,, [J]., 31(3): CAO JINGHE, XIA SHAOHONG, SUN JINLONG, et al, Preliminary results of onshore-offshore seismic experiments in a potential strong earthquake area off the Pearl River Estuary[J]. Journal of Tropical Oceanography, 31(3): (in Chinese)., [D]. : : CAO JINGHE, Research on seismology of littoral fault zone in the Pearl River estuary of northern South China Sea[D]. Guangzhou: South China Sea Institute of Oceanology, Chinese Academy of Sciences: (in Chinese).,,,, OBS [J]., 57(8): NIU XIONGWEI, WEI XIAODONG, RUAN AIGUO, et al, Comparision of inversion method of wide angle Ocean Bottom Seismometer profile: a case study of profile OBS973 2 across Liyue bank in the South China Sea[J]. Chinese Journal of Geophysics, 57(8): (in Chinese).,,,, [J]., 27(4): QIU XUELIN, ZHAO MINGHUI, YE CHUNMING, et al, Ocean bottom seismometer and onshore-offshore seismic experiment in northeastern South China Sea[J]. Geotectonica et Metallogenia, 27(4): (in Chinese)., 颙,,, : [J]., 52(4): QIU XUELIN, CHEN YONG, ZHU RIXIANG, 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[J]. Chinese Science Bulletin, 52(4): ,,,, OBS [J]., 54(12): QIU XUELIN, ZHAO MINGHUI, AO WEI, et al, OBS survey and crustal structure of the Southwest Sub-basin and Nansha Block, South China Sea[J]. Chinese Journal of Geophysics, 54(12): (in Chinese).,,,, : [J]., 31(3): 1 9. QIU XUELIN, ZHAO MINGHUI, XU HUILONG, et al, 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).,,, [M]// 颙. 50. : :

13 : ,,,, OBS [J]., 29(5): WEI XIAODONG, ZHAO MINGHUI, RUAN AIGUO, et al, Identification and application of shear waves along the profile OBS in the mid-northern South China Sea[J]. Journal of Tropical Oceanography, 29(5): (in Chinese ),,,, OBS [J]., 54(12): WEI XIAODONG, RUAN AIGUO, ZHAO MINGHUI, et al, A wide-angle OBS profile across Dongsha uplift and Chaoshan depression in the mid-northern South China Sea[J]. Chinese Journal of Geophysics, 54(12): (in Chinese ),,,, [J]., 28(1): WU ZHENLI, RUAN AIGUO, LI JIABIAO, et al, New progress of deep crust sounding in the mid-northern south China Sea using ocean bottom seismometers[j]. South China Journal of Seismology, 28(1): (in Chinese ),,,, : [J]. :, 41(10): WU ZHENLI, LI JIABIAO, RUAN AIGUO, et al, Crustal structure of the northwestern sub-basin, South China Sea: results from a wide-angle seismic experiment[j]. Science China Earth Sciences, 55(1): (in Chinese),,,, [J]., 31(3): XIA SHAOHONG, LIN WEI, CHEN JIANTAO, et al, Layout of portable stations and signal analysis in an onshore-offshore seismic experiment[j]. Journal of Tropical Oceanography, 31(3): (in Chinese ).,, [M]. : : KORENAGA J, HOLBROOK W S, KENT G M, et al, Crustal structure of the southeast Greenland margin from joint refraction and reflection seismic tomography[j]. Journal of Geophysical Research: Solid Earth( ), 105(B9): NISSEN S, HAYES D, BUHL P, Deep penetration seismic soundings across the northern margin of the South China Sea[J]. Journal of Geophysical Research: Solid Earth, 100(B11): QIU XUELIN, YE SANYU, WU SHIMIN, et al, Crustal structure across the Xisha Trough, northwestern South China Sea[J]. Tectonophysics, 341(1 4): WANG T K, CHEN MINGKAI, LEE C S, et al, Seismic imaging of the transitional crust across the northeastern margin of the South China Sea[J]. Tectonophysics, 412(3 4): YAN PIN, ZHOU DI, LIU ZHAOSHU, A crustal structure profile across the northern continental margin of the South China Sea[J]. Tectonophysics, 338(1): ZHAO MINGHUI, QIU XUELIN, XIA SHAOHONG, et al, Seismic structure in the northeastern South China Sea: S-wave velocity and Vp/Vs ratios derived from three-component OBS data[j]. Tectonophysics, 480(1 4):

14 17.,., Fig. 1 Bougeur gravity map of research region 2 Fig. 2 Magnetic map of research region

14 17.,., Fig. 1 Bougeur gravity map of research region 2 Fig. 2 Magnetic map of research region 1 7 1 Vol. 17 No. 1 2002 3 (13 23) PROGRESS IN GEOPHYSICS March 2002 (,,100101) [ ],, 39.,,. [ ] ; ; [] P738 [] A [ ]100422903 (2002) 0120013211 0,,.,,, NE [1 ],.., ( NE, EW,NE ),.,.,,. 1 20 20 km ( 10