The mayor's proposals for mandatory retrofits target two of the riskiest types of structures built in Los Angeles before 1980: brittle concrete buildings and multi-story wooden buildings supported by weak columns on the ground floor.
Retrofit deadline: 30 years
Cost of retrofit: Varies. Could be more than $1 million for a 10-story building
Affected buildings: About 1,500 need further study to determine if retrofit is needed
Vulnerabilities: Many don't have enough steel reinforcement to hold columns in place during shaking. The collapse of two concrete office towers killed 133 people in a 2011 quake in New Zealand.
Retrofit deadline: 5 years
Cost of retrofit: About $60,000 to $130,000 for a modest-sized apartment building
Affected buildings: About 17,000 need further study to determine if retrofit is needed
Vulnerabilities: These types of buildings have collapsed during both the 1989 Loma Prieta and 1994 Northridge earthquakes. Sixteen people died when the Northridge Meadows apartment complex pancaked.