Research on attenuation relationships for horizontal strong ground motions in Sichuan--Yunnan region

By statistical analyses of 951 sets of acceleration records obtained in several destructive earthquakes and aftershocks of Wenchuan M_S8.0 earthquake, the attenuation relationships for peak ground acceleration (PGA) and acceleration response spectra (damping ratio 0.05) in Sichuan--Yunnan region of China were determined with appropriate attenuation relationship formula and distance parameters. The result of this study indicates that the ground motion induced by larger earthquakes attenuated much slower with the increase of distance than that induced by smaller ones, and the acceleration response spectra for shorter periods (0—0.15 s) attenuated more quickly with the increase of distance than that for longer periods (0.2—10 s), which were the two reasons why considerably large PGA and short-period spectrum acceleration were commonly observed in near-field of moderate earthquakes. But these attenuation relationships could not be used in the determination of design ground motion for engineering sites because of the data incompleteness. The significant difference between the result of this study and the attenuation relationship law in western China obtained with conversion method indicates that further research on the attenuation relationship laws in China is an important and pressing task.