Since I live in
Mordor the Los Angeles metropolitan area, thoughts of the next big earthquake are never too far away. But is the major urban center I live in ready? There's an article on the BBC website discussing the effects of a major earthquake on Los Angeles.
The California Building Code provides for a good probability of a building surviving a large earthquake. But even if a building doesn't collapse, it still may be structurally compromised enough to be red tagged as uninhabitable. And that's just the beginning of the problems.
The infrastructure needed to maintain a major modern population center will be devastated. Water pipes will break, disrupting water supply. Roads and railroads will be damaged and unusable. How will fiber optic lines and cell phone towers fare during an earthquake?
The ports of Los Angeles and Long Beach will probably be mostly intact but getting supplies distributed from them will be difficult. Since a large percentage of the nation's shipping traffic flows through those ports a major quake here would affect the whole country.
Of course the elephant in the corner is the San Onofre Nuclear Generating Station, which is currently being decommissioned.