南海海盆东北部内孤立波的地震海洋学研究
Seismic oceanography study of internal solitary waves in the northeastern South China Sea Basin
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摘要:
以往利用地震海洋学方法发现的内孤立波大多在东沙岛附近，本文在南海海盆东北部首次利用地震海洋学方法发现了海盆中的内孤立波.通过叠前偏移观察该内孤立波细结构的变化，发现内孤立波波形在采集时间段内整体较稳定，内孤立波浅层反射相对深层变化较大.通过改进前人的方法，利用共偏移距道集叠前偏移剖面计算内孤立波视相速度.该方法比直接使用共偏移距道集拟合的共中心点-炮点对曲线线性更好，其计算的内孤立波视相速度为0.82 m·s-1，内孤立波视传播方向为从NW向SE（172°N方向，0°指向北）.
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关键词:
- 地震海洋学 /
- 内孤立波 /
- 南海海盆 /
- 结构特征 /
- 传播特征
Abstract:In previous work,the internal solitary waves (ISWs)discovered by seismic oceanography are mostly near the Dongsha Island. This paper uses the method of seismic oceanography to find the ISWs in the basin for the first time in the northeastern South China Sea. The pre-stack migration is used to examine the changes of the ISWs structure. It is found that the ISWs waveforms are stable overall during the acquisition period. The shallow reflection of the ISWs has a relatively larger change than the deep. By improving the methods of the predecessors,the ISWs apparent phase velocity is calculated by pre-stack migration profile using the Common Offset Gather (COG). The fitting curve of CMP (Common Mid-Point)-shot point pairs using this method has a better linearity than that using Common Offset Gather directly. The apparent phase velocity of this ISWs using the improved method is 0.82 m·s-1,and the apparent direction of the ISWs propagation is from NW to SE (172°N,0° pointing north).
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Key words:
- Seismic oceanography /
- Internal solitary wave /
- South China Sea Basin /
- Structural characteristics /
- Propagation characteristics
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图 1
研究区测线位置分布
Figure 1.
Distribution of multi-channel seismic data
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图 2
改进的内孤立波视相速度计算流程(点划线框中的，虚线框中是 Tang等(2014)的流程)
Figure 2.
The calculation process of improved internal solitary wave apparent phase velocity (in the dash dot box), the process in the dotted box is from Tang et al.(2014)
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图 3
计算内孤立波相速度示意图
Figure 3.
Schematic diagram of the internal solitary waves phase velocity calculation
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图 4
(a) 20号测线内孤立波部分地震叠加剖面(经过叠后FK倾角滤波，只显示了54~98 km的水平范围以及0~1125 m的垂向范围).测线采集时间为2009年4月14日—2009年4月16日；(b)对炮集(2460炮)切除直达波；(c)对CMP道集(CMP 12260)进行动校正，红线标记出了动校拉伸切除位置
Figure 4.
(a) Internal solitary wave part seismic stacked section in line 20 (after post-stack FK dip angle filtering, only the portion of horizontal and vertical ranges of 54~94 km and 0~1125 m, respectively, is shown). Line acquisition time is April 14th—April 16th, 2009; (b) Cut the direct wave on the shot gather (shot 2460); (c) Do NMO on the CMP gather (CMP 12260), and the red line marks the position for cutting the correction stretch
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图 5
20号测线内孤立波振幅随深度变化
Figure 5.
The amplitude of the internal solitary wave varies with depth in line 20
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图 6
(a) T7_39计算的均方根速度; (b) T7_40计算的均方根速度; (c) T7_41计算的均方根速度
Figure 6.
(a) The root mean square velocity calculated by T7_39; (b) The root mean square velocity calculated by T7_40;(c) The root mean square velocity calculated by T7_41
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图 7
(a)、(b)分别是CMP12060的速度谱和拾取的叠加速度; (c)、(d)同(a)、(b)但对应CMP12500
Figure 7.
(a), (b) are the velocity spectrum of CMP12060 and the stacked speed of picking, respectively; (c), (d) are the same as (a), (b) but CMP12500
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图 8
(a) CMP9000-16000范围速度分析得到的层速度; (b) CMP11060_13694范围速度分析得到的层速度，背景是对应的地震叠加剖面
Figure 8.
(a) Layer velocity obtained by CMP9000-16000 range velocity analysis; (b) Layer velocity obtained by CMP11060_13694 range velocity analysis
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图 9
20号测线叠前偏移观察内孤立波细结构变化
Figure 9.
Pre-stack migration of the line 20 is used to observe the fine structure change of the internal solitary wave
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图 10
(a) 利用共偏移距叠前偏移去噪后的剖面拾取内孤立波波谷对应的CMP号; (b)利用共偏移距叠前偏移去噪后的剖面拾取内孤立波波谷对应的炮号; (c)是对COG进行叠前偏移拟合的CMP-炮点对曲线; (d)是直接利用COG拟合的CMP-炮点对曲线
Figure 10.
(a) Pick up the CMP number corresponding to the internal solitary waves trough using the pre-stack migration denoised profile with common offset; (b) Pick up the shot number corresponding to the internal solitary waves trough using the pre-stack migration denoised profile with common offset; (c) The fitting CMP-shot pair curve for pre-stack migration of COG; (d) The fitting CMP-shot pair curve directly with COG
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图 11
(a) KdV计算的线性相速度; (b)不同模态对应的特征函数，其中黑线对应的是第一模态内孤立波，红线对应的是第二模态，绿线是第三模态; (c) KdV拟合内孤立波振幅，黑色线段是内孤立波振幅的垂向变化，红色曲线是使用内孤立波延伸深度(H=1000)获得的理论振幅分布，蓝线曲线是使用海底深度(H=3030 m)获得的理论振幅分布
Figure 11.
(a) The linear phase velocity calculated by KdV; (b) The characteristic function corresponding to different modes, where the black line corresponds to the first mode internal solitary wave, and the red line corresponds to the second mode, the green line is the third mode; (c) is the internal solitary wave amplitude in the KdV fit, the black line segment is the vertical variation of the internal solitary wave amplitude, and the red curve represents the theoretical amplitude acquired using the ISW extension depth (H=1000 m), and the blue line represents the theoretical amplitude distribution acquired using seafloor depth (H=3030 m)
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图 12
20号测线采集时对应的地转流速及海平面高度
Figure 12.
The corresponding geostrophic velocity and sea surface height during the acquisition of the line 20
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图 13
CMEMS物理海洋模型给出的20号测线温度剖面
Figure 13.
The line 20 temperature profile given by the CMEMS physical ocean model
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