It's worth the matinee price just to see the special effects. I'm serious - the devastation is spectacular in every meaning of the word.
And Dwayne "The Rock" Johnson actually acts in the film, which was kinda surprising.
But the plot, what there is of it, is.... I was going to say "secondary" to the disaster porn, but that wouldn't be right. Not even "tertiary." What's the expression for fifth- or sixth-order of importance?
But turn off your plot-hole analyser, shut down your "it doesn't work like that!" processor, set your brain to "numb," and watch Los Angeles and San Francisco collapse in glorious big-screen style. (I saw it in 2D. I've read that 3D mutes the colors somewhat.)
And try not to enjoy it too much. Remember, if it ever does happen who will be footing the bill.
(*Yes, I know Irwin Allen didn't make Earthquake!, but he was the king of disaster porn movies in the 70's.)