马起杨, 许力生, 严川, 李春来, 许康生. 2016: 小江断裂带北段地壳浅层P波速度各向 异性观测的原理与数值试验. 地震学报, 38(1): 15-42. DOI: 10.11939/jass.2016.01.002
引用本文: 马起杨, 许力生, 严川, 李春来, 许康生. 2016: 小江断裂带北段地壳浅层P波速度各向 异性观测的原理与数值试验. 地震学报, 38(1): 15-42. DOI: 10.11939/jass.2016.01.002
Ma Qiyang, Xu Lisheng, Yan Chuan, Li Chunlai, Xu Kangsheng. 2016: Observation of P-wave velocity anisotropy of the shallow crust in the northern Xiaojiang fault zone: Principle and numerical tests. Acta Seismologica Sinica, 38(1): 15-42. DOI: 10.11939/jass.2016.01.002
Citation: Ma Qiyang, Xu Lisheng, Yan Chuan, Li Chunlai, Xu Kangsheng. 2016: Observation of P-wave velocity anisotropy of the shallow crust in the northern Xiaojiang fault zone: Principle and numerical tests. Acta Seismologica Sinica, 38(1): 15-42. DOI: 10.11939/jass.2016.01.002

小江断裂带北段地壳浅层P波速度各向 异性观测的原理与数值试验

Observation of P-wave velocity anisotropy of the shallow crust in the northern Xiaojiang fault zone: Principle and numerical tests

  • 摘要: 以二维情形下观测速度场为各向同性场和各向异性场的叠加为前提, 提出了一种利用走时残差估算地震波速度各向异性的方法, 即剩余慢度矢量法. 利用小江断裂带北段巧家流动地震台阵24个台站记录的3181次地震事件的P波走时残差, 采用剩余慢度矢量法计算了各观测台站周围水平方向上尺度为0.5°×0.5°, 震源深度为0—5 km的剩余慢度矢量, 由此得到了P波快波和慢波方向. 计算结果表明, 大部分观测台站周围的P波速度方向性较为一致, 快波方向为ESE向, 慢波方向为NNE向. 快波方向与小江断裂带北段应力场P轴方向较为一致, 而慢波方向与应力场T轴方向一致, 表明应力的长期作用可能是导致P波速度各向异性的重要原因.

     

    Abstract: This paper proposes a new technique, residual slowness vector technique (RST), for estimating anisotropy of the seismic velocity using the resi-duals of traveling times assuming that 2-D observed velocity field is taken as the superposition of anisotropic field and isotropic one. And then the technique is applied to P traveling time residuals of 3181 events recorded by 24 stations of the Qiaojia Array, a mobile array of seismic broadband stations installed across the northern Xiaojiang fault zone. The residual slowness vectors are calculated within a scale of 0.5°×0.5° in the horizontal direction and 0—5 km in the vertical direction around the observation stations. Finally the polarization directions of the fast P-velocity and slow P-velocity are obtained at all the stations by using the RST. The results show that the directions of the P-velocity at most of the stations are in good agreement. The fast-P directions point to ESE, which nearly agrees with the P axis direction of stress field in northern Xiaojiang fault zone, while the slow-P directions point to NNE, which nearly agrees with the T axis direction, implying that long period of stress action might be one of the important factors causing the P wave velocity anisotropy in this region.

     

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