Abstract

The travel‐time averaged near‐surface shear‐wave velocity to 30 m (VS(30)) is a key parameter for classifying sites in many building codes. Using the travel‐time averaged shear‐wave velocities at two different depths (VS(z1) and VS(z2), and z1<z2<30  m), a new method for estimating VS(30) from a shallow shear‐wave velocity profile measured in a borehole is proposed. Using the data from 594 boreholes from the KiK‐net in Japan and 135 boreholes from California where the shear‐wave velocity profile reaches at least 30 m, the reliability of the new method is validated by both the correlations between the measured and the estimated VS(30) and the accuracy of site classification using the estimated VS(30). The results show that the new method can estimate VS(30) with high accuracy, and the Pearson correlation coefficients between the measured and the estimated VS(30) equal 0.999, and the site classification successful ratio using the estimated VS(30) is greater than 96%, whereas z1≥10  m and z2=25  m. Using the data from Japan, the correlations between the measured and the estimated VS(z) at six depths (50, 100, 150, 200, 400, 600 m) were studied. The results show that the accuracy for the estimating VS(z) (z≥50  m) using the proposed method increases when the selected two depths (z1, z2) are approaching to the depth z as it should be. Compared with methods of Boore (2004) and Boore et al. (2011), the new method does not need any regression analysis to derive empirical relations from a large number of sites, is not regionally dependent, has a remarkable improvement in the accuracy, and is potentially useful for many parts of the world.

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