Traditional seismic design assumes that the lower stories of a building are stronger than the upper stories ; where this is not the case — if the lower story is less strong than the upper structure — the structure will not respond to earthquakes in the expected fashion . Using modern design methods , it is possible to take a weak lower story into account . Several failures of this type in one large apartment complex caused most of the fatalities in the 1994 Northridge earthquake
1994 Northridge earthquake
1994 Northridge earthquake
Seismic retrofit