Not just a movie: the facts on the San Andreas Fault Dwayne Johnson, left, as Ray, and Carla Gugino as Emma, in a scene from the action thriller, "San Andreas" (- AP photos)
Not just a movie: the facts on the San Andreas Fault
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The San Andreas Fault awakens. It unleashes back-to-back jolts that leave a trail of misery from Los Angeles to San Francisco. Skyscrapers crumble. Fires erupt. The letters of the famous Hollywood sign topple. Tsunami waves swamp the Golden Gate Bridge.

Hollywood's favorite geologic bad guy is back in the movie "San Andreas." It's a fantastical look at one of the world's real seismic threats.

The San Andreas has long been considered one of the most dangerous earthquake faults. That's because of its length. At nearly 800 miles long, it cuts through California like a scar. It is responsible for some of the largest shakers in state history.

In the film, a previously unknown fault near the Hoover Dam in Nevada ruptures. It jiggles the San Andreas. Southern California is rocked by a powerful magnitude-9.1 quake. That is followed by an even stronger magnitude-9.6 in Northern California.

U.S. Geological Survey seismologist Susan Hough accompanied The Associated Press to an advance screening of the film. Despite the implausible plot, she said the San Andreas will indeed break again. It will happen without warning.

"We are at some point going to face a big earthquake," she said.

The San Andreas is notorious for producing big quakes. But a magnitude-9 or larger is virtually impossible. It's because the fault is not long or deep enough, Hough noted.

The 1960 magnitude-9.5 quake off Chile is the world record holder.

The San Andreas has revealed its awesome power before. In 1906, a magnitude-7.8 reduced parts of San Francisco to fiery rubble. Nearly five decades earlier, a similar-sized quake rattled the southern end of the fault.

In 2008, the USGS led a team of 300 experts that wrote a script. It detailed what would happen if a magnitude-7.8 hit the southern San Andreas. They wanted to create a science-based crisis scenario. It could be used for preparedness drills.

The lesson: It doesn't take a magnitude-9 or greater to wreak havoc. Researchers calculated a magnitude-7.8 would cause 1,800 deaths and 50,000 injuries. Hundreds of old brick buildings and concrete structures and a few high-rise steel buildings would collapse.

Computer models show the San Andreas is capable of producing a magnitude-8.3 quake. Anything larger is dubious.

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. They herald a monster quake.

Despite a century of research, earthquake prediction remains elusive. Scientists can't predict when a jolt is coming and are generally pessimistic about ever having that ability. Every warning sign scrutinized has failed. Those signs include animal behavior, weather patterns, electromagnetic signals, atmospheric observations and levels of radon gas in soil or groundwater.

"We wish it were as simple as the movie portrays. It isn't. Researchers have scoured every imaginable signal trying to find reliable precursors. But nothing has panned out," Hough said.

The latest focus has been on creating early warning systems. They could give residents and businesses a few seconds heads up after a quake hits, but before strong shaking is felt.

Japan has the most advanced seismic alert system in the world. The U.S. is currently testing a prototype.

Unlike the film, the San Andreas can't spawn tsunamis.

Most tsunamis are triggered by underwater quakes. They can also be caused by landslides, volcanoes and even meteor impacts.

Giant tsunami waves are formed when the Earth's crust violently shifts, displacing huge amounts of seawater. The larger the magnitude, the more these waves can race across the ocean without losing energy.

The San Andreas is a strike-slip fault. That means opposing blocks of rocks slide past each other horizontally. A big San Andreas quake can spark fires and other mayhem. But it can't displace water and flood San Francisco.

Hough said the movie got one aspect right: The tide suddenly ebbing out signals a tsunami is coming.

More than 80 mostly small tsunamis have been observed along California's coast in the past, triggered mainly by faraway quakes.

In the movie, the scientist warned that shaking would be felt on the East Coast. But even the largest possible San Andreas quake won't rattle the East Coast (sorry, New York).

While seismic waves from great quakes can make the Earth resound like a bell, the ringing can only be detected by sensitive instruments because it's so low.

Historical accounts show shaking from the 1906 San Andreas quake was barely felt in western Nevada and southern Oregon, Hough said.

When the ground starts to shake, the seismologist played by Paul Giamatti makes the ideal public service announcement: "Drop, cover and hold on."

Since 2008, millions of people in California and elsewhere have participated in yearly disaster drills. They practice diving under a table and learn other preparedness tips.

If you're outdoors when the ground moves, experts recommend bracing against a wall. It's a tactic similar to what search-and-rescue helicopter pilot Ray Gaines, played by Dwayne "The Rock" Johnson, told scared survivors in the movie.

Critical thinking challenge: Why can't the San Andreas fault cause a tsunami that drowns California?

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COMMENTS (146)
  • LucasF-1
    5/29/2015 - 06:07 p.m.

    The Rocks new movie San Andreas comes out today. It say that a small earthquake triggers a huge one. This is likely because there are huge faults in California. There is a magnitude 9.1 and a 9.7 happens and horrible effects come. I think the movie looks great. I want to go see it.

  • RachelL-2
    5/29/2015 - 09:17 p.m.

    I love this article!!!! It compares the effect that the famous San Andreas fault has in the new movie coming out, and what will actually happen. The San Andreas fault is impossible to predict, even though scientists have been trying predict when the earthquake will hit. They have only been able to tell what won't happen. Scientists know for sure that the quake won't be over a 9.0. They also guarantee that there won't be an additional tsunami that the earthquake causes, since it is in the desert. The San Andres fault runs for 800 miles across California, and when it does hit, (it's said that) 1800 people will die. Good luck to us!!

  • ElleW-3
    5/31/2015 - 07:54 p.m.

    Most people know about the new movie San Andres starring the rock, but it is a real thing that stars all Californians. The San Andrs is a major fault line responsible for countless earthquakes. I am really excited for the movie.

  • Paul-Par
    6/01/2015 - 09:49 a.m.

    I can not believe that an earthquake could injure or kill about 51,800 people at once and break so many stable buildings like brick,concrete, and some high iron buildings.

  • John N
    6/01/2015 - 10:47 a.m.

    I again personally relate to this artcle because I was on a vacation in california and there was a earthquake. It make our hotel shake but the buildings there now are ment for this. It obviously wasn't a big earthquake. The people down their didn't even talk about. It was like the normal for them but we called our family here in wisconsin and they were really nervous and everything.

  • Eriku2
    6/01/2015 - 07:01 p.m.

    This article is about the movie San Andreas. This movie seems unrealistic but a similar event could happen. California is due for a huge earthquake. I think that is haunting to think that this could happen at any time.

  • Steve0620-yyca
    6/01/2015 - 08:18 p.m.

    The San Andreas fault can cause a major earthquake although people said that it wouldn't have a magnitude of 9 because it is not that long or deep. The fault is eight-hundred miles long but not too deep. There might be a chance that the San Andreas fault can separate the cities to the left of it from the United States of America. Earthquakes occur from an epicenter and faults can be dangerous when an earthquake occurs. I hope that the earthquake won't occur for a long time because when it does, it will be a huge disaster.

  • rachelh10503
    6/02/2015 - 08:36 a.m.

    i haven't seen the movie yet, but i will soon. It is good to know where there can be big earthquakes so people that live there are aware of what could happen.

  • barbarat302
    6/02/2015 - 08:40 a.m.

    Wow that's kind of scary that even if the San Andreas fault causes a earthquake it could do a lot of damage to the cities around it and really close to it !

  • lyndas705
    6/02/2015 - 08:40 a.m.

    Wow, I never knew that there was an actual story behind the movie. Most of the time movies have no background they are just made for entertainment. This article has given me a lot of facts. I cannot wait to see this movie.

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