 Earthquakes,
“Mega Quakes,” and the Movies
See also:
Earthquake Facts and Earthquake
Fantasy
California
Department of Conservation Statement
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Lights! Cameras! Disasters!
Throughout the history of Hollywood, disaster films have been sure-fire
winners for moviemakers. Beginning with “The Wind” in
1928, Americans have been plagued by a “Twister” and
“The Perfect Storm.” And we’ve survived “Volcano”
and “Earthquake” and “The Swarm” all followed
by “Armageddon.” That’s not even mentioning us
getting through “The Towering Inferno” and finally making
it to “The Day After.”
With amazing special effects, it’s easy to get caught up
in the fantasy disaster epic. But real-world science is often at
odds with Hollywood. What makes a great science fantasy film often
bears no relation to real facts or the hazards people truly face.
The U.S. Geological Survey is
the lead federal agency responsible for researching, monitoring
and forecasting geologic hazards such as earthquakes, volcanoes
and landslides. And we have the further responsibility to educate
Americans about the real hazards they face and to separate science
fact from science fantasy.
Since earthquakes are featured in the most recent offering in the
made-for-television disaster film genre, let’s start with
some science-based information on them.
Big earthquakes are naturally occurring events well outside
the powers of humans to create or stop. An earthquake is
caused by a sudden slip on a fault, much like what happens when
you snap your fingers. Before the snap, you push your fingers together
and sideways. Because you are pushing them together, friction keeps
them from slipping. When you apply enough stress to overcome this
friction, your fingers move suddenly, releasing energy. The same
“stick-slip” process goes on in the earth. Stresses
in the earth's outer layer push the side of the fault together.
The friction across the surface of the fault holds the rocks together
so they do not slip immediately when pushed sideways. Eventually
enough stress builds up and the rocks slip suddenly, releasing energy
in waves that travel through the rock to cause the shaking that
we feel during an earthquake.
Unlike finger-snaps, earthquakes typically originate several
to tens of miles below the surface of the Earth. It takes
many years – decades to centuries – to build up enough
stress to make a large earthquake, and the fault may be tens to
hundreds of miles long. The scale and force necessary to produce
earthquakes are well beyond our daily lives. Likewise, people cannot
prevent earthquakes from happening or stop them once they’ve
started – giant nuclear explosions at shallow depths, like
those in some movies, won’t actually stop an earthquake.
 It’s
well known that California, the Pacific Northwest and Alaska all
have frequent earthquakes, some of which are quite damaging. Some
areas of the country are more at risk than others, but, in fact,
38 states have an earthquake risk. A map of seismic
hazards in the United States is shown here, and a larger version
can be found here.
The two most important variables affecting earthquake damage
are the intensity of ground shaking caused by the quake and the
quality of the engineering of structures in the region.
The level of shaking, in turn, is controlled by the proximity of
the earthquake source to the affected region and the types of rocks
that seismic waves pass through en route (particularly those at
or near the ground surface). Generally, the bigger and closer the
earthquake, the stronger the shaking. But there have been large
earthquakes with very little damage either because they caused little
shaking or because the buildings were built to withstand that shaking.
In other cases, moderate earthquakes have caused significant damage
either because the shaking was locally amplified, or more likely
because the structures were poorly engineered.
People can’t stop earthquakes from happening. People
can significantly mitigate their effects by identifying hazards,
building safer structures, and learning about earthquake safety.
Meanwhile, let’s clear up a few other things:
The idea of a “Mega-Quake” – an earthquake of
magnitude 10 or larger – while theoretically possible—is
very highly unlikely. Earthquake magnitude is based in part on the
length of faults -- the longer the fault, the larger the earthquake.
The simple truth is that there are no known faults capable of generating
a magnitude 10 or larger “mega-quake.”
 Then
there’s this business of California falling off into the ocean.
NOT TRUE! The ocean is not a great hole into which California
can fall, but it is itself land at a somewhat lower elevation with
water above it. It’s absolutely impossible that California
will be swept out to sea. Instead, southwestern California is moving
ever so slowly (2 inches per year) towards Alaska as it slides past
central and eastern California. 15 million years (and many earthquakes)
from now, Los Angeles and San Francisco will be next-door neighbors.
Another popular cinematic and literary device is a fault that opens
during an earthquake to swallow up an inconvenient character. But
unfortunately for principled writers, gaping faults exist only in
movies and novels. The ground moves parallel to a fault during an
earthquake, not away from it. If the fault could open, there would
be no friction. Without friction, there would be no earthquake.
Shallow crevasses can form during earthquake induced landslides,
lateral spreads, or other types of ground failures. Faults,
however, do not gape open during an earthquake.
So when you see the next big disaster film, rest assured that movies
are just entertainment. Enjoy them! And then go learn about the
real-world science behind disasters and if you live in an area where
hazards exist, take the suggested steps to protect you and your
family.
For more factual information on earthquakes, earthquake
myths and earthquake preparedness see the Earthquake
Facts and Earthquake Fantasy sheet that accompanies this sheet
and visit:
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