Revealing mistake: When the earthquake begins, a dam moves wildly, but the water underneath remains still, revealing it's a camera effect. (00:05:56)
Revealing mistake: During the jolt by the dam, the worker's table shakes, but not the rest of the stuff surrounding them, revealing that someone was moving the table underneath. (00:05:58)
Revealing mistake: During the car chase (an obvious rear projection), Lew keeps turning the steering wheel around despite the car driving straight. (00:09:39)
Revealing mistake: When the earthquake starts there are several shots of churches shaking. None of the trees next to them are shaking, revealing the camera effect. (00:52:16)
Revealing mistake: After Miles' track falls down, there's a shot of a wobbling black office building. It is a mere photograph being very obviously moved back and forth. (00:52:56)
Revealing mistake: During the earthquake, when the window-shop bursts, the airbag that breaks the windows is very, very noticeable. (00:53:13)
Revealing mistake: When Corry's bridge wobbles, the trees and objects in the background don't, revealing that someone was shaking the bridge. (00:54:10)
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)
Revealing mistake: When the parking lot collapses, there's a brick pillar that not only does it not break into pieces, but it bounces around, revealing it's a hollow light-weight prop. (01:38:26)
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: When the airplane is coming in for a landing, we see an exterior shot of the plane shaking violently well before it has touched down. Clearly the "earthquake" effect is achieved by merely shaking the camera.
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: When the elevator crashes, there's a really crappy splat of blood on screen that appears abruptly, which is a very obvious over-impression of a painting.
Revealing mistake: After failing to spin the loop in the motorcycle the first time, Miles tries again. He starts driving towards the loop, and after he finishes the first half, if you look carefully, the bike then falls out of the loop. For the rest of the scene, he continues to ride the bike around the second half of the loop anyway. The shot of him riding towards the loop was probably a previous take.
Revealing mistake: When the executive at Royce's offices looks out of the window to the building across, you can see that the two people deliberately fell out of the window, instead of accidentally falling through.
Revealing mistake: When the earthquake strikes, there's a shot of a tall black glass building shaking. Check the lampposts and buildings around and you'll notice that it's a very obvious film negative being distorted by just wobbling it back and forth.
Revealing mistake: When the earthquake starts there are several shots of bell towers shaking. The first is the only one that moves, the rest are photos where neither the bells nor the trees around move, an obvious camera trick.
Revealing mistake: When Miles is doing his act, he is replaced by an obvious stunt with a different skin color and rounder face.
Revealing mistake: When the group is trying to escape the office building, a woman in pink falls into the void. Watch when she falls and you'll notice that the stuntman's wig flies off (it's to the left of his head).
Revealing mistake: When the California Seismological Institute collapses, the old boss is replaced by a much younger stunt. Also, his sleeves swap between rolled up or not and his tie disappears.
Answer: There are two versions of the film. A 'film' version which does not include this scene (and others) and a 'TV Miniseries' version. The miniseries version was made to run over two nights and extra scenes were shot to extend the running time.
jle