Seismic Site Classification from Surface Wave Data to Vs,30 without Inversion: Fid-Bau Portal

Seismic Site Classification from Surface Wave Data to Vs,30 without Inversion

Lin, Shibin / Gucunski, Nenad / Shams, Sadegh / Wang, Yujin

Surface wave methods have been extensively employed to estimate time-averaged shear-wave velocity ( $V_{s}$ ) to $30 m$ ( $V_{s, 30}$ ) for seismic site classification. However, the inversion of surface wave dispersion data for $V_{s}$ profiling is inherently computationally intensive. To overcome the challenge involved in surface-wave inversion, a new method is proposed to directly estimate $V_{s, 30}$ from surface wave fundamental-mode dispersion data without inversion. The new method is based on the concept that the phase velocity of surface waves ( $V_{R}$ ) at a given frequency ( $f$ ) is proportional to the average shear-wave velocity of soils within one-half of the wavelength ( $λ = V_{R} / f$ ). The proposed method starts from calculating the $V_{s}$ of the top layer as it can be directly estimated from the phase velocity of surface waves whose half wavelengths are smaller than the thickness of the top layer. Likewise, the $V_{s}$ of the second layer can be deduced from the top layer $V_{s}$ along with the phase velocity of surface waves whose half wavelengths are within the thickness range of the second layer. Through such a repetition of sequence-deduction, the $V_{s} s$ of the other layers can be calculated. This method is verified with five case studies that cover typical geotechnical sites. Results indicate that the proposed method can obtain a similar $V_{s, 30}$ with the same site classification for seismic design in comparison with invasive tests and inversion techniques.