Full microtremor H/V(z,f) inversion for shallow subsurface characterization
Full microtremor H/V(z,f) inversion for shallow subsurface characterization
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DOI：
10.1093/gji/ggv132
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发表时间：
2015-07-01
影响因子：
2.8
通讯作者：
Krueger, Frank
中科院分区：
文献类型：
--
作者：
Lontsi, Agostiny Marrios;Jose Sanchez-Sesma, Francisco;Krueger, Frank
H/V谱比作为地震环境噪声分析领域内的单站方法已经出现，因为其能够快速估计场地处的共振频率并通过反演平均剖面信息。虽然它很容易从实验数据计算，它的反理论部分是不明显的，当建立一个前向模型，可以帮助重建导出的H/V谱。这导致了噪声波场主要由瑞利波组成的简化假设，并且导出的H/V经常未经进一步校正而使用。此外，只有右（和左）侧翼周围的H/V峰值频率被认为是在地下一维剪切波速度剖面反演。Sanchez-Sesmaet等人提出了一种新的解释H/V谱比的理论方法。本文介绍了他们理论背后的基本思想，因为它适用于深度接收器。通过考虑精细积分步骤，获得了在宽频率范围上的平滑H/V（z，f）谱曲线，该精细积分步骤又是耗时的。我们表明，对于实际的目的和反演的背景下，这可以大大优化，通过使用粗积分步骤结合相应的方向能量密度（DED）谱的平滑。进一步的分析表明，利用绿色函数虚部平均法计算得到的H/V（z，f）谱，也可以用震源照明介质井的反射率法恢复。对半空间上的单层进行了合成H/V（z，f）谱曲线的反演。惊人的结果允许潜在地使用新的理论作为H/V（z，f）的正演计算，以完全反演在相应深度的剪切速度剖面（Vs）的实验H/V频谱比，此外，使用接收器在表面和深度的压缩速度剖面（Vp）。我们使用在德国的两个选定地点记录的频率范围为0.2-50 Hz的地震环境噪声数据，其中钻孔信息也可用。将所获得的一维Vs和Vp剖面与地质测井信息进行了对比。并与浅层地球物理实验结果进行了对比。
The H/V spectral ratio has emerged as a single station method within the seismic ambient noise analysis field by its capability to quickly estimate the frequency of resonance at a site and through inversion the average profile information. Although it is easy to compute from experimental data, its counter theoretical part is not obvious when building a forward model which can help in reconstructing the derived H/V spectrum. This has led to the simplified assumption that the noise wavefield is mainly composed of Rayleigh waves and the derived H/V often used without further correction. Furthermore, only the right (and left) flank around the H/V peak frequency is considered in the inversion for the subsurface 1-D shear wave velocity profile. A new theoretical approach for the interpretation of the H/V spectral ratio has been presented by Sanchez-Sesmaet al. In this paper, the fundamental idea behind their theory is presented as it applies to receivers at depth. A smooth H/V(z, f) spectral curve on a broad frequency range is obtained by considering a fine integration step which is in turn time consuming. We show that for practical purposes and in the context of inversion, this can be considerably optimized by using a coarse integration step combined with the smoothing of the corresponding directional energy density (DED) spectrum. Further analysis shows that the obtained H/V(z, f) spectrum computed by the mean of the imaginary part of Green's function method could also be recovered using the reflectivity method for a medium well illuminated by seismic sources. Inversion of synthetic H/V(z, f) spectral curve is performed for a single layer over a half space. The striking results allow to potentially use the new theory as a forward computation of the H/V(z, f) to fully invert the experimental H/V spectral ratio at the corresponding depth for the shear velocity profile (Vs) and additionally the compressional velocity profile (Vp) using receivers both at the surface and in depth. We use seismic ambient noise data in the frequency range of 0.2-50 Hz recorded at two selected sites in Germany where borehole information is also available. The obtained 1-D Vs and Vp profiles are correlated with geological log information. Results from shallow geophysical experiment are also used for comparison.