In the movie, while Lex Luthor is explaining his evil plan to Man of Steel, he reveals that he plans to set off a massive earthquake that will cause California to "fall into the ocean".

This is simply not what would happen during a massive earthquake. Two continental plates are sliding parallel to each other along the San Andreas fault. Occassionally, the two plates get stuck, pressure builds up, then eventually releases, which is what causes earthquakes.

So in the case of a huge earthquake, nothing "falls into the ocean". What happens is that one plate shifts up and the other shifts down. Ottisburg would still have been landlocked.