Abstract: By analyzing the records from stiff sites, soft sites and liquefied sites in 2011 Ms 6.3 New Zealand earthquake, the characteristics and relationship of ground motion on 3 types of sites including the liquefied sites are investigated. The seismic acceleration records at 23 seismic stations whose epicenter distances are less than 50 km and PGA great than 0.05g are collected, in which 3 stiff sites, 11 soft sites and 9 liquefied sites are included. The comparison results of amplification coefficient spectra from 3 types of sites indicate that there are obvious distinction among the stiff sites, soft sites and liquefied sites. From the view of ground motion, the liquefied sites can become an independent type. On the liquefied sites the high frequency component of ground motion decreases and meanwhile the low frequency component significantly amplifies. Compared with non-liquefied sites, the response of the short period structure on the liquefied sites will be reduced by half; but at the same time, the response of long period structure on the liquefied sites will be amplified by 2.5-5.0 times. The influence of liquefaction on the damage of CTV building in Christchurch City in the earthquake is significant because the predominant period of acceleration spectra increased to 0.5-1.0 s from 0.1-0.3 s, which is tallied with the natural period of the building about 0.7 s; and the response of the building increases as the consequence. As a result, the existing structure design method would be dangerous for the structures with long period in the liquefiable sites and the seismic ground motion in the liquefiable sites should be specially considered from the viewpoint of vibration.

Key words: New Zealand earthquake, liquefaction, seismic ground motion