Journal of Tropical Oceanography >
Data processing and phase identification of OBS2019-2 in Nansha Block*
Copy editor: YIN Bo
Received date: 2021-11-22
Revised date: 2022-01-18
Online published: 2022-01-19
Supported by
National Natural Science Foundation of China(42174110)
National Natural Science Foundation of China(42176081)
National Natural Science Foundation of China(41674092)
Key Special Project for Introduced Talents Team of Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou)(GML2019ZD0204)
The survey of OBS2019-2 line was carried out across the continent-ocean transition zone (COT) near the Liyuexi Trough of the Nansha Block. This work is critical as it is able to reveal the crustal structure and study rifting-breakup mechanism of the southern continental margin of the South China Sea (SCS). The data of OBS2019-2 is also important to make a comparative study of conjugate continental margin of SCS. Compared with the northern continental margin, there is fewer Ocean Bottom Seismometer (OBS) survey lines and deep crustal structure study in the southern continental margin of SCS. Therefore, more work needs to be done on OBS2019-2. This paper focuses on the data processing workflow of OBS2019-2, including UKOOA file preparation, data format conversion, position relocation, single station seismic record section drawing, etc. Then different kinds of deep seismic phases (e.g. Pg, PcP, PmP, Pn) are identified and traced. These seismic phases are subsequently verified by the travel-time calculation using Rayinvr software. The results of data processing show that deep seismic phases in the seismic record profiles are distinct. The farthest seismic phase could be continuously traced up to 120 km away. Seismic data of OBS2019-2 are of high quality, which can provide a solid foundation for subsequent velocity modeling and structural interpretation.
GUO Jian , QIU Xuelin , LI Zizheng , HUANG Haibo . Data processing and phase identification of OBS2019-2 in Nansha Block*[J]. Journal of Tropical Oceanography, 2022 , 41(5) : 43 -56 . DOI: 10.11978/2021162
图1 南海区域地形及主要深地震测线位置[据丘学林等(2012)修改]黑色实线为深地震测线, 红色实线为本研究的OBS2019-2测线。该图基于国家测绘地理信息局标准地图服务网下载的审图号为GS(2016)1609的标准地图制作 Fig. 1 The bathymetric map and main deep seismic survey lines in the South China Sea (modified from Qiu et al, 2012). Black lines show the locations of deep seismic survey lines. Red line indicates the OBS2019-2 survey line |
图2 南沙地块OBS2019-2测线位置与水深地形图红色点为数据处理成功的站位, 黑色点为数据异常的站位, 白色点为仪器丢失的站位, 图中数字表示OBS站位编号 Fig. 2 The bathymetry map and location of OBS2019-2 in the Nansha Block. Red markers are the stations with successful data processing. Black points are the stations with abnormal data. White dots are the positions of lost instruments. The numbers in the figure indicate the OBS station number |
图4 OBS10台站直达水波震相位置校正前(a)和校正后(b)对比折合速度为6.0km·s-1。图中红色点表示拾取的直达水波震相走时, 紫色虚线用于判断直达水波的对称性 Fig. 4 Contrast of direct water phases (Pdw) before and after the relocation of OBS10. The reduced velocity is 6.0 km·s-1. The red points show the trave-times of direct water phases we picked and the purple dashed lines are used to judge the symmetry of direct water phases |
表1 OBS2019-2测线OBS位置校正结果Tab. 1 OBS relocation results of OBS2019-2 |
站位 编号 | OBS 编号 | 投放点位置 | 校正后位置 | 校正后 水深/m | RMS/ms | t_adjust/s | ||
---|---|---|---|---|---|---|---|---|
经度/E | 纬度/N | 经度/E | 纬度/N | |||||
01 | A37 | 115°05′35.48″ | 12°49′05.95″ | 115°05′40.02″ | 12°49′06.31″ | 4360 | 2.6 | -3.033 |
02 | L26 | 115°07′43.72″ | 12°44′24.97″ | 115°07′51.46″ | 12°44′28.46″ | 4361 | 1.3 | -0.144 |
03 | S11 | 115°09′51.84″ | 12°39′43.92″ | 115°09′46.73″ | 12°39′40.97″ | 4363 | 1.8 | -0.117 |
04 | L23 | 115°12′00.40″ | 12°35′03.62″ | 115°11′48.66″ | 12°34′58.58″ | 4358 | 3.4 | -0.124 |
05 | L85 | 115°14′07.84″ | 12°30′21.82″ | 115°14′09.71″ | 12°30′20.84″ | 4360 | 1.2 | -1.157 |
06 | B41 | 115°16′15.74″ | 12°25′40.76″ | 115°16′11.39″ | 12°25′40.58″ | 4357 | 1.4 | -0.011 |
07 | L54 | 115°18′23.54″ | 12°20′59.68″ | 115°18′19.80″ | 12°20′59.53″ | 4359 | 1.5 | -0.144 |
08 | L16 | 115°20′31.31″ | 12°16′18.55″ | 115°20′44.09″ | 12°16′24.71″ | 4357 | 1.9 | -0.126 |
09 | H56 | 115°22′38.96″ | 12°11′37.43″ | 115°22′24.17″ | 12°11′32.75″ | 4357 | 1.5 | -0.108 |
10 | L17 | 115°24′46.55″ | 12°06′56.30″ | 115°24′48.20″ | 12°07′00.08″ | 4359 | 1.9 | -0.130 |
11 | B29 | 115°26′54.06″ | 12°02′15.14″ | 115°26′31.38″ | 12°02′07.55″ | 4369 | 3.1 | -2.928 |
12 | L94 | 115°29′01.50″ | 11°57′33.95″ | 115°28′58.40″ | 11°57′33.95″ | 4326 | 0.7 | -1.115 |
13 | L96 | 115°31′08.87″ | 11°52′52.75″ | 115°31′09.48″ | 11°52′54.84″ | 4328 | 2.2 | -0.111 |
14 | L93 | 115°33′16.16″ | 11°48′11.56″ | 115°33′22.93″ | 11°48′14.18″ | 4321 | 1.7 | -0.122 |
15 | L35 | 115°35′23.39″ | 11°43′30.32″ | 115°35′12.37″ | 11°43′25.46″ | 4332 | 2.0 | -0.028 |
17 | B87 | 115°39′37.62″ | 11°34′07.86″ | 115°39′22.03″ | 11°34′00.05″ | 4070 | 2.3 | -0.027 |
18 | L70 | 115°41′45.31″ | 11°29′27.67″ | 115°41′31.38″ | 11°29′21.12″ | 3936 | 1.4 | -0.115 |
19 | L98 | 115°43′51.56″ | 11°24′45.29″ | 115°44′03.70″ | 11°24′49.57″ | 3104 | 3.3 | -0.076 |
20 | L95 | 115°45′58.43″ | 11°20′03.98″ | 115°45′38.92″ | 11°19′55.81″ | 2700 | 1.8 | -0.093 |
23 | B40 | 115°52′18.59″ | 11°05′60.00″ | 115°52′18.84″ | 11°06′00.07″ | 2142 | 4.2 | 0.039 |
24 | L31 | 115°54′25.20″ | 11°01′18.66″ | 115°53′52.12″ | 11°01′04.76″ | 2675 | 5.2 | -2.093 |
25 | L64 | 115°56′31.70″ | 10°56′37.28″ | 115°56′36.89″ | 10°56′40.06″ | 2350 | 5.5 | -0.099 |
27 | D28 | 116°00′44.57″ | 10°47′14.50″ | 116°00′43.31″ | 10°47′14.32″ | 2114 | 3.1 | -0.192 |
28 | L89 | 116°02′50.89″ | 12°49′05.95″ | 116°02′50.82″ | 10°42′33.16″ | 2228 | 3.5 | -1.893 |
29 | H52 | 116°04′57.14″ | 12°44′24.97″ | 116°04′43.25″ | 10°37′45.48″ | 2103 | 2.1 | 0.068 |
30 | L99 | 116°07′03.07″ | 12°39′43.92″ | 116°07′02.82″ | 10°33′09.86″ | 1794 | 3.9 | 0.054 |
图5 OBS2019-2邻近测线的地壳结构剖面a. OBS973-2测线的地壳结构剖面[据阮爱国等(2011)]; b. OBS973-1测线的地壳结构剖面[据丘学林等(2011)]; c. CFT-OBS2011测线南沙地块区域的地壳结构剖面[据Pichot等(2014)] Fig. 5 The cross-section of crustal structure adjacent to the OBS2019-2. (a) The crustal structure profile of OBS973-2 (Ruan et al, 2011); (b) The crustal structure profile of OBS973-1 (Qiu et al, 2011); (c) The crustal structure profile of CFT-OBS2011 in the Nansha Block (Pichot et al, 2014) |
图6 OBS11台站垂直分量的震相识别与射线追踪a. 垂直分量综合地震记录剖面与震相识别(折合速度为6.0km·s-1); b. 震相走时拟合情况(黑色细线表示理论计算走时, 彩色粗线表示实际拾取走时); c. 初始纵波速度模型与射线追踪 Fig. 6 Seismic phase identification and the travel-time ray tracing in the vertical component of seismic record of OBS11. (a) The seismic record profile and the seismic phase identification (the reduced velocity is 6.0 km·s-1); (b) Travel-time fitting (the black thin lines show the calculated travel-times and the thick colored lines show the picked travel-times); (c) The initial model of P-wave and ray-tracing of the seismic phases |
图7 OBS14台站垂直分量综合地震记录剖面与震相识别a. 垂直分量综合地震记录剖面与震相识别(折合速度为6.0km·s-1); b. 震相走时拟合情况(黑色细线表示理论计算走时, 彩色粗线表示实际拾取走时); c. 初始纵波速度模型与射线追踪 Fig. 7 Vertical component of the seismic record in OBS14 and the seismic phase identification. (a) The seismic record profile and the seismic phase identification (the reduced velocity is 6.0 km·s-1); (b) Travel-time fitting (the black thin lines show the calculated travel-times and the thick colored lines show the picked travel-times); (c) The initial model of P-wave and ray-tracing of the seismic phases |
图8 OBS17台站垂直分量综合地震记录剖面与震相识别a. 垂直分量综合地震记录剖面与震相识别(折合速度为6.0km·s-1); b. 震相走时拟合情况(黑色细线表示理论计算走时, 彩色粗线表示实际拾取走时); c. 初始纵波速度模型与射线追踪 Fig. 8 Vertical component of the seismic record in OBS17 and the seismic phase identification. (a) The seismic record profile and the seismic phase identification (the reduced velocity is 6.0 km·s-1); (b) Travel-time fitting (the black thin lines show the calculated travel-times and the thick colored lines show the picked travel-times); (c) The initial model of P-wave and ray-tracing of the seismic phases |
图9 OBS23台站垂直分量综合地震记录剖面与震相识别a. 垂直分量综合地震记录剖面与震相识别(折合速度为6.0km·s-1); b. 震相走时拟合情况(黑色细线表示理论计算走时, 彩色粗线表示实际拾取走时); c. 初始纵波速度模型与射线追踪 Fig. 9 Vertical component of the seismic record in OBS23 and the seismic phase identification. (a) The seismic record profile and the seismic phase identification (the reduced velocity is 6.0 km·s-1); (b) Travel-time fitting (the black thin lines show the calculated travel-times and the thick colored lines show the picked travel-times); (c) The initial model of P-wave and ray-tracing of the seismic phases |
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