A regional ground-motion model for vertical-to-horizontal spectral acceleration ratios in Southwestern China
摘要
Strong seismic activity in southwestern China poses a serious threat to public safety. Though ground motion models (GMMs) are essential for ensuring that structures have sufficient seismic capacities, only the horizontal GMMs have been extensively obtained for southwestern China; few vertical GMMs have been developed. Owing to the lack of near-field records for large earthquakes in this region, this study established a model for predicting the vertical-to-horizontal spectral acceleration (V/H) ratios using an empirical reference approach. The results indicate that the predicted V/H ratios for southwestern China increased with increasing earthquake magnitude, particularly for short-period motions. The short-period V/H ratios decreased with increasing source distance, whereas the trend was the opposite for the long-period V/H ratios. Furthermore, the short-period V/H ratios decreased, then remained nearly constant with increasing VS30 (where VS30 is the average shear-wave velocity to 30 m depth), whereas the long-period V/H ratios consistently increased. Additionally, the results indicate that the peak V/H ratio in soil site in near-field was larger than 2/3 with a maximum value of 1.68. Finally, the residuals of the adjusted model showed no significant bias regarding the predictor variables, and the V/H ratio curve predicted by the adjusted model crossed through the center of the recorded V/H ratio data. Thus, the adjusted model derived in this study showed good agreement with observed data in southwestern China and can be used as a reference for seismic design in this region.