This paper presents a study of the dynamic analysis of a building before 

and after devastating earthquakes using system identification. The eight storey reinforced concrete building is instrumented with 10 accelerometers. The time domain N4SID system identification technique was used to obtain the frequencies, damping ratios and mode shapes considering fixed and pseudo flexible base models taking into account the soil-structure-interaction. The response of the building before and after the Darfield (04/09/2010) and Christchurch (22/02/2011) earthquakes was ascertained to evaluate the significant changes in the behavior. It was concluded from the investigation that monitoring the seismic response of the building is useful for a better understanding of its behaviour during earthquakes, and also that the participation of soil is significant towards 

the seismic response of the building and it should be considered in models to simulate the real behavior.