• ISSN 2097-1893
  • CN 10-1855/P

利用接收函数PmS和PPmS约束全地壳方位各向异性

Constraining whole crustal azimuthal anisotropy using PmS and PPmS phases of receiver functions

  • 摘要: 地壳各向异性是研究地震活动与地壳动力学演化的重要依据,接收函数莫霍面P-S转换波PmS到时随反方位角的周期性变化被广泛应用于约束地壳各向异性特征. 受地震活动分布不均匀、部分地震台站记录周期偏短、莫霍面上下介质复杂多变及环境噪声等影响,一些接收函数PmS震相无法准确识别或缺失,使得利用PmS约束地壳各向异性存在一定的局限性. 本文提出联合应用PmS和PPmS测量全地壳各向异性参数的方法,分别求取两种震相由各向异性导致的到时扰动,获得平均扰动值,并使用非线性拟合方法计算各向异性参数;在PPmS信号质量显著优于PmS的情况下,也可单独应用前者约束各向异性. 本文将该方法应用于不同信噪比的合成地震记录以及实际观测地震数据中,综合测试验证了此方法测量全地壳方位各向异性的有效性.

     

    Abstract: Crustal anisotropy plays a crucial role in the study of seismic activity and crustal dynamic evolution, which is widely constrained based on the periodic variation of moveout of the P-to-S conversion at the Moho (PmS) with respect to the back azimuth in receiver functions (RFs). Due to the uneven distribution of seismic activity, short recording period, complexity of mediums adjacent to the Moho, and presence of ambient noise, some PmS phases in RFs have no well-determined arrivals, which impedes the use of PmS to constrain crustal anisotropy. In this study, we propose a new method of jointly applying PmS and PPmS phases to measure crustal anisotropy parameters. First, perturbations of moveout caused by presence of azimuthal anisotropy are obtained by averaging those of the PmS and PPmS after subtracting the corresponding values in isotropic cases. After that, those perturbations are plotted against the back azimuth, and fitted using a cosine function. The optimal pair of anisotropy parameters corresponds to the best fitting curve. When PPmS is characterized by a higher signal-to-noise ratio than the PmS, we can only use the former to constrain crustal anisotropy. Tests using synthetic and observed seismic records with various signal-to-noise ratios confirm the applicability of the method in measuring whole crustal azimuthal anisotropy.

     

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