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I have a confession to make: I love disaster porn. I don’t mean actual porn where the boom mic is visible…I mean terrible movies with huge death tolls. I loved The Day After Tomorrow, and 2012, and Volcano, and Dante’s Inferno, and Armageddon, and Deep Impact, which again is not actual pornography despite the name.
So I’m very excited for The Rock’s new movie, San Andreas, which promises to show the obliteration of the West Coast, which I currently call home. We’ve actually had a few rumbles in the past couple of days, which may just be ingenious viral marketing for the movie, I’m not sure.
As much as I love the cheesy acting and the brilliant special effects of most disaster porn, I think my favorite part is always the bad science. And judging from the trailer, it looks like San Andreas will not disappoint on that front.
First of all, according to the film’s official website, the earthquake that destroys California in the film is a magnitude 9.0. According to geologists, the maximum magnitude of the San Andreas fault is 8.1. That may not sound like much of a difference, but the magnitude scale is logarithmic, meaning that the 9.0 earthquake is 8 times bigger than the 8.1 earthquake and 22 times stronger.
Second of all, would a large San Andreas fault earthquake cause a tsunami to destroy San Francisco?
Probably not, no. That tsunami in the trailer for San Andreas looks impressive, but unless it was caused by a different earthquake or maybe an asteroid coincidentally landing in the ocean just after the San Andreas earthquake, it’s probably not very realistic.
The reason has to do with what kind of fault the San Andreas is: transform. Transform faults occur when two tectonic plates are moving horizontally past one another: in this case, you can picture what’s happening by thinking of how San Francisco, which is on the North American plate, is slowly getting closer to Los Angeles, which is on the Pacific plate. How nice! I have a lot of friends in LA.
The types of earthquakes that can result in tsunamis occur at convergent faults, meaning that the two plates are running into each other. When one plate is oceanic and the other is land, the oceanic one is heavier, causing it to go under the other plate, which is called “subduction.” That causes it to pop up in other places and displace a whole lot of water. That water then moves toward the land and becomes a tsunami.
That doesn’t mean that California can’t experience a tsunami. The Gorda plate, up by the Pacific Northwest, does form a convergent fault with the North American plate, resulting in subduction zone that has sent waves to Northern California and Oregon. The biggest tsunami to hit the west coast in modern times happened in 1964, when an earthquake in Alaska caused a tsunami to travel down the coast, killing dozens of people. The worst hit town was Crescent City in northern California, where the harbor acts as a sort of tsunami focuser. That town actually gets loads of tsunamis, though usually they aren’t the devastating kind that we’re all so familiar with.
Anyway, I’m not sure how the film will explain their tsunami, but I won’t be holding my breath waiting for a rational explanation other than “it’s a disaster film on the West Coast so we basically have to destroy the Golden Gate Bridge in a fun way or people will be horribly disappointed.” But good luck to those people in the trailer who take cover from the wave hurling a cruise ship at their high-rise by hiding behind a pillar. They’re going to need it.