Aftershocks following an earthquake can be damaging to the built environment, as observed in New Zealand during 2010 and 2011. In this paper, the aftershock sequence is discussed and a soil-foundation-structure numerical model is introduced. The numerical model represents a 9-story, inelastic, steel, eccentrically braced frame structure founded on a shallowly-embedded mat foundation. Soil foundation-structure interaction effects were explicitly considered by employing nonlinear Winkler springs. The model was subjected to the 22 February 2011 Christchurch Earthquake and two larger aftershocks, and the progressive seismic damage was tracked. Results show that for this type of structure, the seismic damage caused by the aftershocks is negligible compared to the mainshock. More modelling effort is needed to examine the progressive damage of other soil-foundation-structure models.