Abstract:The study of long-period ground motions is significant to seismic design of large-scale engineering structures. The digital broad-band seismic records of strong earthquake swarm obtained in Jiashi,Xinjiang,China,in 1997 are used to study the impact of earthquake magnitude and focal mechanism on long-period ground motions. The results show that:(1) Earthquake magnitude has strong effects on the long-period ground motions. Larger earthquake has more long-period ground motion contents. (2) Compared with the strike-slip earthquakes,the oblique-faulting earthquakes have more long-period contents in vertical component. (3) The long-period horizontal acceleration response spectra of strike-slip earthquakes are higher than those of the normal-faulting earthquakes.