Estimation of Time-Averaged Shear Wave Velocity (SWV) to 30 m considering Site SWV Structural Characteristic

The time-averaged shear wave velocity (SWV) to 30 m (V_S30) is a site condition parameter that has been widely used to specify the site class in building codes. However, the penetration depth of some building sites is less than 30 m, and thus,V_S30cannot be determined based on the velocity profiles. To estimate the site parameterV_S30accurately, we examined the effect of the velocity structural characteristic parameter of site profiles,β_H, onV_S30by performing a residual analysis. Further, a method to estimateV_S30was established considering the effect ofβ_H, and the validity of the proposed model was assessed based on site data pertaining to Japan and California (USA). The results show that the time-averaged shear wave velocity to the depthH(H < 30 m),V_SH, is weakly correlated with the parameterβ_H. However,β_Hhas a significant effect onV_S30; for the same siteV_SH,V_S30tended to increase withβ_H. Compared with the extrapolation method, the proposed model can significantly reduce the standard deviation for the estimation ofV_S30, while increasing the correlation between the estimated and measured values ofV_S30. Thus, the estimation accuracy can be significantly improved by considering the effect ofβ_H.

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