A New Model for Estimating V_S30 Based on Engineering Boreholes Data

The average shear wave velocity to a depth of 30 m below the ground surface （V_S30） is an important parameter for evaluating the site condition and the site earthquake response. There are a large number of borehole data with depths of less than 30 m in China, and these borehole data cannot be directly used to calculate V_S30 by definition equation code. Under this situation, referencing the correlated research results which include the parameter of V_S30 were prevented. It is important to estimate V_S30 accurately. Using the data of 590 boreholes with depths greater than 30 m in Guanzhong plain of Shaanxi Province to research the V_S30 estimation model. The results show that the average shear wave velocity at different depths (Z<30 m) and the elevation of the borehole have a strong log-linear relationship with the measured value of V_S30 along the depth, so a new model of log-linear extrapolation, which comprehensively considers the average shear wave velocity at different depths and the elevation of the borehole, was proposed. Compared with the velocity gradient extrapolation model and the double-depth parameter extrapolation model, when the calculation depth is smaller, the new model has higher estimation accuracy and better stability, and this advantage is more prominent.