Local site conditions have a significant influence on the seismic ground motions, directly governing the spatial distribution of earthquake disasters. The site classification is fundamental in determining seismic parameters for engineering seismic design. The determination of seismic ground motion parameters for different site conditions plays a crucial role in ensuring the seismic safety of engineering structures. The classification index of the site, the determination of the index’s limit value, and the site classification scheme are consistently hot topics in earthquake engineering. This paper aims to compare the effects of different site classification methods in China, the United States, and Japan on determining ground motion parameters, particularly on seismic design for engineering structures. By analyzing ground motion attenuation relationships for different site classes, it can be revealed how different site conditions affect spectral characteristics of ground motions. This provides more accurate ground motion parameters for seismic design, and offers theoretical support and practical guidance for earthquake disaster risk assessment, engineering seismic design, and relevant policy formulation.

Based on the borehole data of 646 observation stations and the acceleration time history data of 25 275 pairs of horizontal strong motions recorded by KiK-net, the site conditions of selected stations were classified according to 12 site classes divided by the site classification methods from China, the United States, and Japan. The strong motion records were then classified and grouped based on the 12 site classes, resulting in 12 strong motion record datasets. Subsequently, the spectral acceleration （including peak ground acceleration） of each record was calculated. The spectral acceleration dataset for each site class was statistically regressed separately, and then the corresponding spectral acceleration attenuation relationships were obtained for the 12 site classes. The difference in spectral accelerations for different site classes calculated using those attenuation relationships is significant as it reflects the site effects on ground motions. A comparison was made regarding differences in the spectral characteristics of ground motions on different class sites. Finally, a comprehensive analysis and comment were presented based on research results.

This study conducted a regression analysis of ground motion attenuation relations and obtained the attenuation law of spectral accelerations for 12 class sites. The study also analyzed the influence characteristics of site condition on the spectral accelerations of ground motions. When comparing and analyzing the spectral characteristics of ground motions on different class sites, it was found that Chinese and American site classification methods can clearly distinguish the influence of different site conditions on the spectral characteristics of ground motions, while Japanese classification method struggles to do so. Specifically, there is almost no overlap between the normalized spectral acceleration curves obtained from Chinese and American classification methods, indicating significant differences in the effects of different site classes on ground motion. On the other hand, it is showed that Japanese classification method was no significant differences in calculated values of normalized spectral accelerations except for class I sites, especially class Ⅲ and Ⅳ sites. Furthermore, it was revealed that overall standard deviation of ground motion attenuation relation calculated by Chinese classification method was lower than that by American and Japanese classification methods. Moreover the clustering and consistency of within-site classifications by Chinese classification method were stronger compared with the other two approaches.

After conducting an in-depth study of ground motion attenuation relationships and site classification methods, the following conclusions have been drawn. The site classification methods used in China and the United States are able to effectively reflect the significant differences in spectral characteristics of ground motion among different class sites. They can capture better the influence of site conditions on spectral characteristics of ground motion. However, it is noted that the discriminability of spectral characteristics among different class sites in Japanese classification method is not sufficient.

In comparison with the classification methods employed in the United States and Japan, it was observed that the Chinese classification method demonstrates a higher level of clustering and consistency in terms of ground motion at different sites. On the other hand, it was found that Japanese classification method exhibits a lower discriminability and may even fail to adequately reflect variations in site effects across different class sites. These findings offer key theoretical support and practical advice for earthquake risk assessment, seismic design, and policy-making.