Data processing and seismic phase identification of OBS converted shear wave in the Xisha Block
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摘要:
主动源海底地震仪（OBS）转换横波震相的分析和模拟，能够从泊松比的角度更准确地约束地下结构和物质组成，有助于地壳精细结构和构造属性的研究.本文对南海北部陆缘西沙地块的OBS2013-3测线进行了转换横波数据处理和分析，通过能量扫描法求取极化角，并对OBS水平分量数据进行旋转，获取了径向分量数据.结合本测线的地质情况，求解佐布里兹（Zoeppritz）方程，得到了不同转换模式的能量分配关系，定量地指示了沉积基底和海底面为主导的P-S转换界面，Moho面为次一级转换界面.在OBS2013-3测线的各个台站径向分量地震剖面上识别出了一系列PPS和PSS型转换震相，最大偏移距达到130km，并进行了初步的正演模拟试算和验证.结合本测线实际情况，对OBS转换横波研究的基础问题进行了探讨.这些工作为后续的二维横波速度结构和泊松比结构模拟、物质组成和地壳属性分析打下了坚实的基础，为研究方法的进一步完善提供思路.
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关键词:
- 西沙地块 /
- 海底地震仪(OBS) /
- 转换横波 /
- 震相识别 /
- 转换界面
Abstract:Analysis and simulation of converted seismic shear wave phases recorded by active-source Ocean Bottom Seismometer (OBS) provide accurate constrains on subsurface structures and lithological compositions from aspect of Poisson's ratios, which can facilitate research on detailed crustal structures and tectonic affinity. Processing and analysis of seismic shear wave phases are carried out on OBS2013-3 traversing the Xisha Block, the South China Sea margin. Radial component data is obtained through rotating horizontal components using polarization angles calculated by energy scanning method. Zoeppritz equations are solved based on the geological conditions, which yields the energy partition of different conversion modes, indicating the dominant P-S conversion interfaces of sedimentary basement and seafloor as well as the secondary one of the Moho. A series of PPS and PSS type converted shear wave phases are identified in radial components of most stations of OBS2013-3, whose maximum offset reaches 130 km. Preliminary forward ray-tracing is conducted to verify the identified phases. Based on actual conditions of this profile, we also discuss some fundamental issues in OBS converted shear wave studies. Above work could lay a solid foundation for subsequent 2-D shear wave velocity or Poisson's ratio modelling and crustal composition analysis, as well as inspire further improvement of research methods.
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图 1
西沙海域海底地形与OBS2013-3测线位置图
Figure 1.
Bathymetric and topographic map of Xisha area, showing location of OBS2013-3
图 2
OBS主动源探测地震波P-S转换模式示意图
Figure 2.
Schematic diagrams of P-S wave conversion in active-source OBS prospecting
图 3
罗盘角校正前后分量旋转效果对比(以OBS11台站径向分量为例)
Figure 3.
Comparison between component rotations using recorded and calculated compass angle (take the radial component of OBS11 as an example)
图 4
OBS06台站第3158道(偏移距约20km)质点运动轨迹对比
Figure 4.
Particle motion comparison of seismic trace 3158 in OBS06
图 5
基于Zoeppritz方程计算的转换波反射、透射系数分布
Figure 5.
Plots on amplitude coefficients of reflective and transmissive converted waves based on Zoeppritz equations
图 6
OBS11台站转换S波PPS型震相识别与射线追踪
Figure 6.
Identification and ray-tracing of PPS type converted S-wave seismic phases in OBS11
图 7
OBS11台站转换S波PSS型震相识别与射线追踪
Figure 7.
Identification and ray-tracing of PSS type converted S-wave seismic phases in OBS11
图 8
OBS2013-3测线识别的主要转换S波震相
Figure 8.
Main converted S-wave seismic phases identified in OBS2013-3
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