The new Dwayne Johnson movie "San Andreas" is a heart-pumping thrill ride, a throwback to the people-in-peril disaster flicks that Irwin Allen made in the 1970s but with state-of-the-art special effects. Directed by Brad Peyton, written by Carlton Cuse and opening May 29, the movie centers on a search and rescue pilot (Johnson) determined to save his estranged wife (Carla Gugino) and teenage daughter (Alexandra Daddario) when a magnitude-9.2 earthquake hits California.

The plot has several coincidental contrivances bordering on the preposterous that can be overlooked in the name of dramatic license, but it also takes liberties with the earth science at the heart of the story. What's fact and what's fiction? We asked seismologist Jean-Paul Ampuero, professor of geophysics at California Institute of Technology, who has not yet seen "San Andreas," to weigh in and separate reel fantasy from real science.

In 'San Andreas,' we're told that we're overdue for a big earthquake on the San Andreas Fault. True?

Yes. The last time a big earthquake hit the southern end of the San Andreas Fault was more than 150 years ago. Just based on the history of previous earthquakes, you could expect it could happen any time soon.

Could it be as big as a magnitude-9?

A 9 would be too big; I'd say an 8. When we do the earthquake drill every year, the scenario with which we work for a plausible large earthquake is 7.8 to 8.

The movie's earthquake is 9.2.

Those earthquakes happen in Japan, in Chile. It could happen in Washington state or Oregon, but not here. The reason is the tectonics are different. The San Andreas Fault is a fault that slips mainly horizontally, whereas in Japan or the Pacific Northwest or Alaska the fault is mainly moving vertically. Those other places generate bigger earthquakes. The whole Ring of Fire, the so-called Subduction Zones, can host huge earthquakes. So we're lucky in California.

In the movie, an earthquake in Nevada triggers the San Andreas. Could this happen?

No. The fault systems are not connected. The major earthquakes happen at the plate boundaries, which are very close to the coast, the whole Ring of Fire. There are some earthquakes on the interior of the plate, like the New Madrid [Missouri] Zone, but they're not connected to the San Andreas. But it is possible that one earthquake can trigger another — that what makes aftershocks.

A huge tsunami drowns San Francisco in the movie. How big does an earthquake have to be to trigger a tsunami?

You need two things: a magnitude of 8 or larger, and you need it to happen off shore, which is not the case for the San Andreas Fault. To create a big tsunami you need to move a big mass of water. Since the San Andreas is inland, and doesn't move vertically, it wouldn't make a big tsunami. Some of the other faults in California are offshore; they don't have major vertical movement but they could trigger an underwater landslide that could cause a small tsunami, not the kind we've seen in Indonesia, Japan and Chile.

The Caltech scientist played by Paul Giamatti in the movie has developed a technology to predict earthquakes. How plausible is that?

We wish we could do it! We all dream someday that we'll be able to do it. But there's half the [seismology] community that thinks it's impossible and we will never be able to do it. We don't know at this point if we will be able to in the future. What we do know is how to prepare for an earthquake, how to evaluate what can happen and how to do earthquake early warning — sending a warning tens of seconds before the earthquake arrives.

Paul Giamatti and Archie Panjabi in the film 'San Andreas'

Paul Giamatti (left) and Archi Panjabi take cover during a scene in "San Andreas." (Photo: Jasin Boland/Warmer Bros.Pictures)

Are we really better prepared for earthquakes now?

Yes. With every earthquake there have been lessons and improvements in the way we deal with and educate the public about earthquake preparedness. Many of the types of damage that occurred during the 1994 Northridge earthquake would not happen today. New constructions have very strict standards to follow, and there has been real retrofitting, But in some instances it's just recommendations and the responsibility of owners to do the retrofitting. What the state government is doing is trying to figure out how to help people finance this type of retrofitting.

Are there positive things about a disaster movie, even if Hollywood gets it wrong?

Yes. It's part of the business to put some drama in it, but it's an educational opportunity. The good thing is it can bring attention to the fact that an earthquake is a real threat and to be able to talk about it can educate the public. The downside is that if we don't take that opportunity, people will leave the theater thinking, "There's nothing I can do!" We can do a lot. We can survive and recover from a large earthquake if we prepare well for it.

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The science behind 'San Andreas'
Caltech seismologist Jean-Paul Ampuero separates fact from fiction in this fun but faulty movie.