The newer things (like subway tunnels and more flexible skyscrapers) are engineered for it. Building codes in Los Angeles have become gradually more earthquake-compatible since the 1930s. Current buildings can ride out a lot of energy.

Older things (like, for instance, the 1930s-vintage cast-iron Santa Monica feeder, a major water line that runs under Sunset Boulevard) sometimes break. But that happens even when there's no earthquake. The lines simply get shut off at the nearest valve and repaired.