The Faults in the Movie, San Andreas

Credit: Mark Legg
This map shows the California Borderland and its major tectonic features, as well as the locations of earthquakes greater than Magnitude 5.5. Large arrows show relative plate motion for the Pacific-North America fault boundary.
Map abbreviations stand for the following:  
BP = Banning Pass  CH = Chino Hills  CP = Cajon Pass  LA = Los Angeles  PS = Palm Springs
V = Ventura  ESC = Santa Cruz Basin  ESCBZ = East Santa Cruz Basin Fault Zone
SCI = Santa Catalina Island  SCL = San Clemente Island  SMB = Santa Monica Basin
SNI = San Nicolas Island 


On Friday, May 29th, the movie San Andreas premiered to mixed critical reaction.  In general, movie critics are somewhat positive about the entertainment value, but, question the science behind the movie.  An example is a review that appeared on sfgate.com entitled, “San Andreas’ movie destroying S.F. is great fun, bad science”, by David Perlman, the San Francisco Chronicle’s science editor.

San Andreas is the story of two earthquakes on different sections of the San Andreas Fault that devastates Southern California and is felt across the country even to the East Coast.  The film, written by Allan Loeb, Carlton Cuse, Carey Hayes and Chad Hayes, and based on an original script by Jeremy Passmore and Andre Fabrizio, speculates on what would happen if California did, indeed, suffer the big one, the mother of all earthquakes as long expected and predicted.   The two quakes in the film are triggered by a smaller quake on a previously unknown fault near Nevada’s Hoover Dam, causing a powerful magnitude-9.1 quake on the San Andreas followed by an even stronger magnitude-9.6 in Northern California.  This quake in turn, causes a tsunami to wash through the Golden Gate and flood the cities around San Francisco Bay.

How scientifically accurate is the film?
Morgan Page, a geophysicist with the United States Geological Service (USGS) was quoted in one article, “not very”.  (Page hadn’t seen the film, but viewed trailers.)  USGS seismologist Susan Hough who accompanied The Associated Press to an advance screening of the film was quoted in a syndicated article that, "We are at some point going to face a big earthquake."

Another USGS seismologist Lucy Jones, who previewed the movie last week in California, was quoted in a USA Today article as saying that the movie was "a lousy documentary but a good movie. It was better than I thought it would be."

According to Hough, Jones and Page 
  • A magnitude-9 or larger on The San Andreas is impossible because the fault is not long nor deep enough.  Computer models show the San Andreas is capable of producing a magnitude-8.3 quake, but anything larger is dubious.
    • Strike-slip faults indicate rocks are sliding past each other horizontally, with little to no vertical movement. The San Andreas is a strike-slip. 
  • The 9.6 quake on the San Andreas fault in the film is shown spawning a tsunami that roars through the Golden Gate, flooding the cities around San Francisco Bay.  Likely?  Again, no.  As Page explained, “the San Andreas has slip motion. This isn’t the type of motion that would generate a tsunami wave. You need something like a subduction (quake) where you’re lifting large volumes of water, so it didn’t appear to be realistic.” 
    • Reverse faults, also called thrust faults, slide one block of crust on top of another pushing up mountain ranges such as the Himalayas and the Rocky Mountains.  Geologists use the term "subduction zone" to refer to the boundary between two tectonic plates where one plate “underthrusts” the other and moves into the earth's mantle.  It is these faults in the ocean floor whose motion displaces ocean water to create a tsunami.
    • An example of subduction quake in a reverse fault is the Tohoku quake off the east coast of Japan on 11 March 2011.  This quake is blamed for killing more than 15,000 people, damaging or destroying nearly 400,000 buildings, and damaging the Fukushima nuclear power plant.  The ensuing tsunami resulted from the release of stress between two overlapping tectonic plates (a subduction zone) beneath the ocean floor.  The San Andreas is a slip-zone fault on land; an oceanic subduction quake is needed to cause a tsunami.  However, there are subduction faults in the ocean off-shore of Southern California, but the area most likely to experience a subduction fault quake spawning a tsunami is the coastline between Oregon and Alaska.
  • Then, there’s a shot where the San Andreas Fault appears to open up the Earth. Page says that wouldn’t happen. “The San Andreas fault is not going to open up. It a fault that slides like this; it’s not going to open,” she explained.  
    • Normal faults create space as shown in the film. Two blocks of crust pull apart, stretching the crust into a valley. The Basin and Range Province in North America and the East African Rift Zone are two well-known regions where normal faults are spreading apart Earth's crust.  The Atlantic Ocean was created over millions of years by the spread of a normal fault.
  • In the film, Lawrence Hayes, a fictional seismologist at Caltech (a real university), notices spikes in "magnetic pulses" that light up California like a Christmas tree, heralding a monster quake.  Again, according to Hough, scientists can't predict earthquakes and are pessimistic about ever being able to.
  • In the movie, the scientist warned that shaking would be felt on the East Coast. The truth: even the largest possible San Andreas quake won't be felt on the East Coast.  While seismic waves from great quakes can make the Earth ring like a bell, an earthquake’s frequency is so low it can only be detected by sensitive instruments.
Page did say that while the trailer doesn’t appear to be accurate, she thinks viewers can still learn something from it. “My hope is that the movie just reminds everyone that California is earthquake country and we all need to be prepared.”

Earthquakes
by Bruce Bolt

"A good college primer
on earthquakes.
Easy read and very informative."

Click on image to order
Powell's Books
How important is it that the movie has the science wrong?
On one hand, it’s entertainment, and neither the television nor the movie industries are required to create product that is scientifically sound though a number of movies and shows do have qualified scientific advisers on staff.  

The down side to scientific inaccuracy is that some if not most viewers may likely come away from the movie with a poor understanding of the potential for a major quake and what might happen when it occurs.  Some may even be put at risk by expecting something that is very unlikely to happen.

Other research points out that as much as 50% of a population experiencing a major quake such as the Tohoku quake show symptoms of Post Traumatic Stress Disorder – some showing symptoms of full-blown PTSD within 30 days.

On the other hand, as one scientist wrote in an e-mail to Science News for Writers, “while the information in a movie may not be accurate, if it is sufficiently interesting, it will lead audiences to seek out better resources that provide them with more reliable information.” 

True, people are talking, and that's good. 

My concern is that most viewers of the movie will come away with bad information about the effects of an earthquake and what to expect, heightening their fears. When the Charleton Heston vehicle, Earthquake, came out in 1974 (George Fox, Mario Puzo writers) plate tectonics was just being accepted in the scientific community, and we frankly knew little more about quakes than that they shook like hell.

Also, forty years ago it was more work for a writer or producer to access solid scientific information.  Today, while we’re still learning about earthquakes, we do know so much more than we did then.  Today, this knowledge is simply a mouse click away.

Finally, do we as writers have a moral or ethical responsibility to our audience to try and get the science right in our manuscripts and screenplays?  I suppose some could argue that point, especially about topics like natural disasters where real lives are at risk.  (A side effect of a writer doing research may well be ideas and scenarios they never would have considered without the work.)

What it comes down to your personal choice as an artist.  How much of a sound scientific footing do you want to build under your stories?  What reputation do you want to build in the industry?  At the end of your life, do you want to regret not getting it right for the people who read or watch your work?  

I can’t answer that question, but you can.

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