
Study on active surface wave survey with a high-velocity top layer
HongRui XU, ZePeng LIU, TianJian CHENG, XiaoFei YIN, ShiDa SUN
Prog Geophy ›› 2024, Vol. 39 ›› Issue (4) : 1628-1638.
Study on active surface wave survey with a high-velocity top layer
The dispersive characteristics of high-frequency(≥2 Hz) Rayleigh-wave phase velocities have been widely used to determine the subsurface shear velocity. However, the shear velocity of the surface layers (e.g., < 0.2 m depth) is poorly constrained in the dispersion inversion within tens of hertz. Furthermore, the inverted shear velocity at deeper depths can be biased due to inaccurate shear velocity at surface in dispersion inversion. In practice, both the concrete road under urban environment and rigid ballast bed of railway should be presented as a thin layer of distinct high (>1000 m/s) shear velocity at the surface, the inverted results from dispersion inversion would be largely biased under these abnormal surface environments. Compared to the phase velocity, the Rayleigh-wave Horizontal-to-Vertical (H/V) ratios of particle motion are particularly sensitive to shallower shear velocity. Based on this idea, we propose a method for constructing Vs profiles based on the joint inversion of the Rayleigh-wave phase velocity dispersion and H/V from active-seismic records. According to the inversion results of synthetic data based on the model with high-velocity top layer, the accuracy ofthe shearvelocity[LM]in the surface layer and underlying layers is considerably improved by joint inversion including H/V. The proposed method has great engineering significance for the detection of urban road and railroad bed diseases under high-velocity surface layer conditions.
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