The link at this title goes to a video about the violence.

Toward the end of the video is a tour of the scene shortly after the bombing.  It is initially deadly quiet.  The scene is not as debris laden as I would expect it to be so it was probably a huge concussion bomb of some kind.  Not that it didn't do damage, but, the debris outside the building is morely glass and paper with little structural integrity noted to be scattered about.  The concrete and metal seemed to have held up fairly well.  Of course, concrete and steel holds up better than flesh.


The bomb blast reached a great distance, but, I didn't notice any crater.


There is one car chasis in the film, it could be the vehicle or perhaps not, simply a vehicle at the scene.  I don't think so though unless the gasoline ignited in the explosion.  The damage to that vehicle is considerable and does not seem to match the damage to the buildings.


I would not trust the structural soundness of the buildings for more than a day or so.  These events usually show up structural damage after a settling of the blast.  Even a concussion bomb would 'rattle' the 'seams' enough to start a significant deterioration of the structure in a couple of days to a week.  


Sort of like that of an earthquake, but, localized to one small area.  


My sympathies to such a wonderful country as Norway.  So, sorry to hear such terrible, terrible news.