Some experts are warning it could be the Katrina of Los Angeles. There may be dozens, possibly hundreds of buildings in the city at risk of collapsing in a major earthquake and causing thousands of deaths. These buildings are part of a group called non-ductile concrete structures. Built primarily before 1976, they have weak columns that can become brittle in a major quake, causing collapse. An estimated 2,000 of these buildings stand in L.A. today, a modest share of which — perhaps 5 to 10 percent — may carry the even grimmer distinction of being "killer buildings."