Estimation of Shear-Wave Velocity-Depth Models Using Love Surface Waves Records: a Comparison With Other Seismic Methods

Abstract eng:
Within the methods focused on geotechnical characterization of soils for Civil Engineering applications, geophysical methods have excelled in measuring shear waves due to its effectiveness and low cost compared to traditional invasive methods. Among the geophysical methods, propagation and recording of seismic waves have been the key to measure parameters such as compressional and shear-wave velocities, which are strongly related with the major geotechnical parameters of interest. Because Love and Rayleigh waves provide a large percentage (~70%) of the seismic energy, one of the most widely used techniques is based on dispersion curves modeling of surface waves. The phase velocity of these waves depends mainly on the shear-wave velocity and allows to compute the average Vs30 parameter. This work aims at developing a complete methodology based on Love surface waves analysis to determine one dimensional structures of shear-wave velocity versus depth, and to compare this method with the modeling of refracted SH body waves, and other procedures based on the analysis of Rayleigh surface waves typically used in geotechnical studies, such as MASW and ReMi methods. The Love waves are formed by constructive interference of SH body waves propagating below the earth surface, and their phase velocity depends on frequency, but not on the propagation velocity of the compressional P-wave. This feature represents an advantage in the use of Love instead of Rayleigh waves, decreasing the number of variables required for the modeling of dispersion curves in order to get shear wave velocity-depth models. The application of the Love Surface Wave Method (LSWM) is carried out on seismic SH wave data, acquired using a horizontal source as well as the transversal horizontal component of geophones. Overall, the dispersion curves modeling shows strong sensitivity to the variation of the properties of the medium at high frequencies, indicating good resolution at shallow depths and a decreasing sensitivity and resolution at higher depths, especially in the absence of low frequencies in the records. The comparative analysis between the LSWM and the other seismic methods shows that, at least down to 25 m deep, all the resulting shear wave velocity models are concordant, with a decreasing correlation between them at greater depths probably due to lack of data in frequencies below of 5 Hz and the loss of resolution due to the decreasing sensitivity of dispersion curves at deeper layers.

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