Ground motion prediction equation for the vertical component of 5%-damped spectral acceleration (0.01-10 s) in western China

A ground motion prediction equation (GMPE) that can predict the vertical 5%-damped spectral acceleration (SA) in western China was formulated. To this end, a dataset that included the strong motion recordings of this region was constructed. Explanatory variables for the GMPE were identified, and a full set of final model coefficients was obtained using the random-effects method. We compared the results of this study with those of previously published work and the data of the 2019 Changning Ms 6.0 earthquake. The results indicate that the vertical SA depends on not only magnitude and distance but also the type of the faulting and linear site response. The nonlinear site response and depth to the top of rupture (Ztor) have slight effect on the vertical SA. The residual distribution, which exhibited no obvious relationship with the explanatory variables or the agreement between the predicted and observed vertical SA of the 2019 Changning Ms 6.0 earthquake, suggested good ability for vertical SA prediction in western China. Finally, the vertical-to-horizontal (V/H) ratio is affected by the magnitude, distance, and type of faulting, and near-source V/H ratio curves with respect to period at soil sites and rock sites for large earthquakes exhibit single-peak and double-peak characteristics, respectively.