A fast, robust method for detecting and characterizing azimuthal anisotropy with marine PS converted waves, and its application to the west Svalbard continental slope
A fast, robust method for detecting and characterizing azimuthal anisotropy with marine PS converted waves, and its application to the west Svalbard continental slope
复制标题
一种快速、稳健的海洋 PS 转换波检测和表征方位各向异性的方法及其在西斯瓦尔巴群岛大陆坡的应用
DOI：
10.1111/j.1365-246x.2006.03186.x
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发表时间：
2006
影响因子：
2.8
通讯作者：
G. Westbrook
中科院分区：
文献类型：
--
作者：
R. Haacke;G. Westbrook
摘要
提出了一种利用PS转换波检测和刻画方位地震各向异性的方法，并应用于斯瓦尔巴群岛以西大陆斜坡底部附近采集的四分量海底地震仪数据。该方法确定垂直于矢状面(横向)振动的相干信号的分布，并采用优化的旋转技术来分离各向异性的影响和对地震振幅的其他贡献。经径向对应物归一化的PS波横向振幅的大小与颗粒运动的椭圆度相对应，并被用来约束近地表沉积物中的各向异性对称类。结果表明，存在正交或水平的横向各向同性对称性，这与近垂直、排列的裂纹的存在是一致的。从其方向来看，观测到的各向异性与：(1)沉积序列中的重力下坡应力，向西南倾斜约2度；(2)与北克尼波维奇山脊分段扩展中心有关的构造应力，沿NW-SE方向扩展。定向裂隙可能会影响天然气水合物和游离气在这些沉积物中的局部分布。对地震噪声对优化旋转影响的研究表明，独立检波器记录的矢量组合对源相关噪声具有不同的敏感性。在矢状方位角将检波器的部署方向平分到海床上时，这种灵敏度达到峰值。提出了一种降低方向噪声敏感度的方法，改善了横向幅值图。这种去噪方法可以用来提高多分量地震图像的质量。
SUMMARY
A method for using PS converted waves to detect and characterize azimuthal seismic anisotropy is developed, and applied to four-component ocean-bottom seismometer data acquired near the base of the continental slope west of Svalbard. The method determines the distribution of coherent signal vibrating perpendicular to the sagittal plane (the transverse direction), and employs an optimized rotation technique to separate the effects of anisotropy from other contributions to the seismic amplitude. The magnitude of the PS-wave transverse amplitude, when normalized by its radial counterpart, is shown to correspond to the degree of ellipticity of particle motions and is used to constrain the anisotropic symmetry class in the near-surface sediments. Results indicate the presence of orthorhombic or horizontal, transversely isotropic symmetry that is consistent with the presence of near-vertical, aligned cracks. From its orientation, the observed anisotropy is associated with: (1) gravitational, downslope stresses in the sediment sequence, which dips by approximately two degrees to the SW and (2) tectonic stresses associated with the segmented spreading centres of the northern Knipovich Ridge, which spread in the NW–SE direction. Aligned cracks are likely to influence the local distribution of gas hydrate and free gas in these sediments. An investigation of the effect of seismic noise on optimized rotation shows that the vectorial combination of independent geophone records has variable sensitivity to source-related noise. This sensitivity peaks where the sagittal azimuth bisects the deployment orientation of the geophones on the seabed. A method to reduce the sensitivity to directional noise is developed and shown to improve the transverse amplitude plots. This approach to noise reduction may be used to improve the quality of seismic images derived from multicomponent data.