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 |
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引用本文: | 马起杨,许力生,严川,李春来,许康生. 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[J]. 地震学报, 2016, 38(1): 15-42. DOI: 10.11939/jass.2016.01.002 |
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作者姓名: | 马起杨 许力生 严川 李春来 许康生 |
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作者单位: | 1.中国北京 100081 中国地震局地球物理研究所; |
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基金项目: | 国家自然基金41474046中国地震局地球物理研究所基本业务费专项DQJB14B01 |
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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.
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关 键 词: | 各向异性 P波速度 走时残差 小江断裂带北段 |
收稿时间: | 2015-06-17 |
Observation of P-wave velocity anisotropy of the shallow crust in the northern Xiaojiang fault zone:Principle and numerical tests |
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Affiliation: | 1.Institute of Geophysics, China Earthquake Administration, Beijing 100081, China2.Earthquake Administration of Gansu Province, Lanzhou 730000, China |
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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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