Journal of Tropical Oceanography >
Characteristics of secondary Ps phases recorded by ocean bottom seismometer in the Taiwan Strait and its application
Copy editor: YIN Bo
Received date: 2021-12-22
Revised date: 2022-01-28
Online published: 2022-02-13
Supported by
Youth Science and Technology Fund of Earthquake Administration of Fujian Province(Y202001)
On the ocean bottom seismometer (OBS) wide-angle seismic record section, multiple signals with high energy and good continuity can often be detected. As same as the first arrival phases, multiple phases also can be real reflections of subsurface interfaces, they are generated by the same source signal. However, in the conventional OBS data processing, multiple signs are often deleted as invalid signals, just a few studies are concerned with their properties and applications. By processing the OBS data acquired from Line HXN01 in the southern Taiwan Strait, the secondary phases are identified and picked on eight seismic recording sections. Analysis of the measured data from OBS0106 station reveals that the waveform characteristics and particle motion trajectory of these two phases are very similar, the amplitude of the secondary Ps phases is greater than that of the first arrival phases. Then we determined that the secondary reflecting interface corresponds to the secondary Ps phases by Rayinvr ray tracing simulation. The fitting results of travel time shows that after adding the secondary phases, the ray-coverage density of the shallow sedimentary layer under the station is significantly increased, and the ray-coverage area is also significantly increased, which provides more information for the inversion of sedimentary structure. In addition, the inversion test before and after the addition of the secondary Ps phase was performed on the crustal structure of the theoretical model, and it was found that after the addition of the secondary Ps phase data, the interface depth error of the sedimentary layer improved significantly.
GUO Xiaoran , LIU Shanhu . Characteristics of secondary Ps phases recorded by ocean bottom seismometer in the Taiwan Strait and its application[J]. Journal of Tropical Oceanography, 2022 , 41(5) : 57 -63 . DOI: 10.11978/2021178
图 1 HXN01测线位置图红色五角星为OBS0106台站位置, 红色实心圆为OBS0103台站, 黄色实心圆为丢失或数据存在问题的OBS, 蓝色实心圆为数据正常的OBS, 浅灰色虚线为裂谷隆起带边界, 蓝色点虚线为凹陷边界, 黑色曲线和数字为等深线; 水深数据来自GEBECO_ 2014 (http://www.geobco.net)。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 Location of the profile HXN01. The red five-pointed star is the position of OBS0106, the red circle is OBS0103, and the yellow circle is the OBS with problem and missing data, the blue circle is the OBS with intact data, the gray dashed line is the boundary of rift and uplift zone, the blue pecked line is the boundary of sag. Bathymetric data are from GEBECO_2014 (http://www. geobco.net) |
图2 OBS0106台站(a)和OBS0103台站(b)综合地震记录剖面折合速度为 6.0km·s-1, Ps代表沉积层折射震相, Pg代表地壳内部折射震相, PcP代表地壳内反射震相, PmP代表莫霍面反射震相 Fig. 2 Comprehensive seismic recording profile of OBS0103 (a) and OBS0106 (b). Reduced velocity is 6.0 km·s-1. Ps indicates sedimentary refractive phase, Pg indicates crustal refractive phases, PcP indicates reflective phases from intra-crustal interface, PmP indicates reflective phases from Moho |
图3 OBS0106台站记录到的第5415道初至与二次Ps震相(a)以及波形对比图(b)图中红色波形为二次震相波形 Fig. 3 The primary Ps and secondary Ps phases picked up at the trace No.5415 of OBS0106 station (a) and waveform comparison (b). The red waveform is the secondary phase waveform |
图4 OBS0106台站记录到的初至Ps震相(a~d)与二次Ps震相(e~h)质点运动轨迹图截取时窗分别为1.6~2.0s和3.26~3.66s; 图d和h中红色实线代表径向分量; 黑色实线代表切向分量; 黑色虚线代表垂向分量 Fig. 4 The particle trajectories of the primary phase (a ~ d) and the secondary Ps phase (e ~ h) recorded by OBS0106 station. Time windows are 1.6 ~ 2.0 s and 3.26 ~ 3.66 s; the red solid line represents the diameter component; the black solid line represents the tangential component; the black dashed line represents the vertical component |
图5 初至震相和二次震相的射线追踪与走时拟合图a、c、e为射线追踪示意图; b、d、f为走时拟合示意图。b、d、f中橙色为Ps1震相, 粉色为二次Ps1震相, 草绿色为Ps2震相, 浅蓝色为二次Ps2震相, 黑色实线代表理论走时, 短竖线代表观测走时, 其长短代表拾取走时的不确定性。a、b反射层为海水层和沉积层上层; c、d反射层为沉积层下层; e、f反射层为海水层和沉积层下层 Fig. 5 Ray tracing (a, c, e) and travel time simulation (b, d, f) of first-arrival phase and secondary phase. Orange represents Ps1 phase, light pink represents secondary Ps1 phase, grass green marks Ps2 phase, light blue marks secondary Ps2 phase, the black solid line represents the theoretical travel time, the short vertical line represents the observation travel time, and its length represents the uncertainty in the travel time picking-up. Figures a, b; figures c, d and figures e, f present the results of ray tracing with seawater-upper sediment interface, lower sediment, and seawater-lower sediments as the second reflecting layer |
图 6 沉积层界面反演恢复结果a. 初始模型; b. 利用初至震相数据恢复结果; c. 初至震相与二次Ps震相联合反演震相恢复结果。图中黑色实线为沉积层界面 Fig. 6 Recovery result of sedimentary interface inversion. (a) Initial model; (b) Inversion result using first-arrival phase data; (c) combined inversion result using first-arrival phase data and the secondary Ps phase. The black solid line represents the sedimentary basement |
图7 恢复误差分布图图中红色圆点为初至震相反演得到的界面深度恢复误差, 蓝色圆点为初至震相与二次Ps震相联合反演界面深度恢复误差, 黑色虚线之间为恢复误差±0.5km内范围 Fig. 7 Distribution of inversion errors. The red dots are the interface depth recovery errors obtained from the reverse evolution of the first-arrival phase, the blue dots are the interface depth recovery errors obtained by the joint inversion of the first-arrival phase and the secondary Ps phase. Between the black dotted lines is the recovery error within ± 0.5 km |
图8 OBS0106台站射线覆盖密度图a. 初至震相约束下的射线覆盖密度图; b. 初至震相与二次Ps震相联合约束下的射线覆盖密度图。图中黑色虚线表示速度界面 Fig. 8 Ray density distribution of the OBS0106 station. (a) The ray density distribution of first arrivals; (b) The ray density distribution after the addition of secondary Ps phases. The black solid dashed line represents the velocity discontinuity |
[1] |
丁祥焕, 1999. 福建东南沿海活动断裂与地震[M]. 福州: 福建科学技术出版社. (in Chinese)
|
[2] |
李鹏, 刘伊克, 常旭, 等, 2006. 多次波问题的研究进展[J]. 地球物理学进展, 21(3): 888-897.
|
[3] |
刘洪卫, 刘怀山, 邢磊. 2018. 浅水环境下多次反射折射波条带范围的研究[J]. 海洋地质前沿, 34(12): 14-21.
|
[4] |
吕坚, 高建华, 胡翠娥, 2001. 东南沿海地震带地震活动性及近期形势分析[J]. 地震学刊, 21(4): 18-23, 58.
|
[5] |
邵学钟, 范会吉, 1993. 地震转换波测深中二次反射波震相的识别和利用[J]. 中国地震, 9(3): 3-13.
|
[6] |
石颖, 邢小林, 2011. 表面多次波压制的研究进展: 回顾与展望[J]. 地球物理学进展, 26(6): 2046-2054.
|
[7] |
万奎元, 曹敬贺, 夏少红, 等, 2016. OBS广角地震探测中二次反射Pg震相特征及在地壳结构成像中的作用[J]. 地球物理学报, 59(8): 2818-2832.
|
[8] |
吴振利, 阮爱国, 李家彪, 等, 2012. 南海西南次海盆广角地震探测[J]. 热带海洋学报, 31(3): 35-39.
|
[9] |
杨恺, 郭朝斌, 2012. 多次反射折射波的传播路径研究[J]. 石油地球物理勘探, 47(3): 379-384.
|
[10] |
钟广见, 刘大锰, 冯常茂, 等, 2014. OBS纵波资料镜像叠前时间偏移处理[J]. 热带海洋学报, 33(3): 46-51.
|
[11] |
|
[12] |
|
[13] |
|
[14] |
|
[15] |
|
[16] |
|
[17] |
|
/
〈 | 〉 |