热带海洋学报 JOURNAL OF TROPICAL OCEANOGRAPHY 海洋地球物理学 doi:10.11978/2015132 2016 年第 35 卷第 5 期 : 75 http://www.jto.ac.cn * 陈金虎 1,2, 夏少红 1, 曹敬贺 1, 万奎元 1,2, 丘学林 1.,, 510301 2., 100049 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 : 1009-5470(2016)05-0075-13 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 510301, China 2. University of Chinese Academy of Sciences, Beijing 100049, 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 2015-10-31; 修订日期 : 2015-12-28 基金项目 (913282064157604141276049); 作者简介 (1989),,, E-mail: jinhuchen@scsio.ac.cn * Received date: 2015-10-31; Revised date: 2015-12-28. Editor: SUN Shujie Foundation item: National Natural Science Foundation of China (913282064157604141276049); Program for Distinguished Young Scholars of Chinese Academy of Science Author: CHEN Jinhu. E-mail: jinhuchen@scsio.ac.cn
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,
: 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 0 1 0 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 1 0 0 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
78 Vol. 35, No. 5 / Sep., 2016 1 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 1 6.9 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,
: 79,, 6.9 kms 1 7.0 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,,,
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 1 350.20.515 040002000 1.12523 10.6077 3 2 350.20.515 0100002000 1.42114 11.9211 2 4 350.20.515 010002000 1.33097 11.5367 2 6 5100.20.515 03002000 1.28577 11.3383 2 8 5100.20.515 08002000 1.46657 13.8357 2 : 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 1 23.37%; 6km 8km 77.42% 79.91%,,,, 3, OBS
: 81,,,, 3.1, : 1km, P 1.5kms 1 ; 4km, P 1.7 kms 1 4.6 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),,
82 Vol. 35, No. 5 / Sep., 2016 2, χ 2 1.29774, 1.06007, 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 0.0 3100.20.55 010002000 1.08379 10.4105 2 0.1 3100.20.55 050001000 1.29774 11.3918 2 0.3 3100.20.55 0350002000 1.06007 10.2960 4 : 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
: 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 1 350.20.510 5101005 1.08694 10.4257 2 3 350.20.510 5101005 1.11517 10.5602 3 5 350.20.510 5102005 1.69851 13.0327 2 : OBS 20km,, 10km20km30km,, OBS, : 4, 10km 5km ( 9a); 4, 10km 3km ( 9e) 30km20km10km,, ( 9bd 9fh) 9 bcd, 10km5km, : 30km,,,, ; 20km, 30km,,,
84 Vol. 35, No. 5 / Sep., 2016 9 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,
: 85 10 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
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