Revealing mistake: In the office tower after the quake there is a panic and workers rush down the stairs only to find them fallen away. After two women fall to their death a man is left hanging on a girder, but falls onto a giant piece of glass. Look at the top of the frame and you will see the airbag shooting our from under it.
Revealing mistake: During the quake, a mother is seen having a plate glass window fall on her face while her daughter screams. Before the mother turns around to show us the gore, look close and you can see a shard of glass already "placed" in her face before the fake glass falls her. Additionally, while not a "mistake", it's clearly a "stuntman" portraying the mother. The face and yelping give it away.
Revealing mistake: Near the beginning, after a couple of small earthquakes, Fred comes flying out of the dam elevator shaft with a whole heap of water, dead from drowning. But you can see him lift his head out of the water seconds before his friend turns him over and finds him definitely dead.
Revealing mistake: When the parking lot building collapses, check the right side where the cars are. All along the ground level there's a rectangular strip where the film of the miniature building was pasted on top of the film with the real-sized parked cars. Note how all the debris falls behind that strip, it never falls on top of the cars, as if there was a weird black hole of some sort. (01:37:54)