The building 's engineering is unusual because of the placement over the transit tunnel , and for other reasons . Part of the structure is cantilevered over the 1985 load-bearing columns that did not match the later building 's design . Because of the tunnel , four buildings are designed as one seismic unit , including a rubber membrane serving as a joint between all the buildings and 505 Union Station . It was the first building in Seattle with perimeter moment frame design since the 1994 Northridge earthquake , which exposed national safety concerns requiring re-review of this technique
1994 Northridge earthquake
1994 Northridge earthquake
Opus Center