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In 132 CE,
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Chinese polymath Zhang Heng
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presented the Han court with
his latest invention.
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This large vase, he claimed,
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could tell them whenever an earthquake
occurred in their kingdom–
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including the direction
they should send aid.
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The court was somewhat skeptical,
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especially when the device triggered
on a seemingly quiet afternoon.
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But when messengers came
for help days later,
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their doubts turned to gratitude.
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Today, we no longer rely on pots to
identify seismic events,
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but earthquakes still offer a unique
challenge to those trying to track them.
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So why are earthquakes so
hard to anticipate,
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and how could we get better
at predicting them?
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To answer that,
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we need to understand some theories
behind how earthquakes occur.
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Earth’s crust is made from several vast,
jagged slabs of rock
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called tectonic plates,
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each riding on a hot, partially molten
layer of Earth’s mantle.
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This causes the plates to
spread very slowly,
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at anywhere from 1 to 20
centimeters per year.
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But these tiny movements are powerful
enough
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to cause deep cracks in the
interacting plates.
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And in unstable zones,
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the intensifying pressure may
ultimately trigger an earthquake.
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It’s hard enough to monitor these
miniscule movements,
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but the factors that turn shifts into
seismic events are far more varied.
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Different fault lines juxtapose
different rocks–
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some of which are stronger–or weaker–
under pressure.
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Diverse rocks also react differently to
friction and high temperatures.
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Some partially melt, and can release
lubricating fluids
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made of superheated minerals
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that reduce fault line friction.
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But some are left dry,
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prone to dangerous build-ups of pressure.
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And all these faults are subject to
varying gravitational forces,
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as well as the currents of hot rocks
moving throughout Earth’s mantle.
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So which of these hidden variables
should we be analyzing,
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and how do they fit into our
growing prediction toolkit?
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Because some of these forces occur
at largely constant rates,
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the behavior of the plates
is somewhat cyclical.
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Today, many of our most reliable clues
come from long-term forecasting,
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related to when and where earthquakes
have previously occurred.
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At the scale of millennia,
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this allows us to make predictions
about when highly active faults,
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like the San Andreas,
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are overdue for a massive earthquake.
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But due to the many variables involved,
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this method can only predict
very loose timeframes.
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To predict more imminent events,
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researchers have investigated the
vibrations Earth elicits before a quake.
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Geologists have long used seismometers
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to track and map these tiny shifts
in the earth’s crust.
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And today, most smartphones are
also capable
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of recording primary seismic waves.
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With a network of phones around the globe,
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scientists could potentially
crowdsource a rich,
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detailed warning system that alerts
people to incoming quakes.
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Unfortunately, phones might not be able
to provide the advance notice needed
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to enact safety protocols.
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But such detailed readings
would still be useful
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for prediction tools like NASA’s
Quakesim software,
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which can use a rigorous blend of
geological data
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to identify regions at risk.
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However, recent studies indicate
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the most telling signs of a quake might be
invisible to all these sensors.
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In 2011,
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just before an earthquake struck
the east coast of Japan,
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nearby researchers recorded surprisingly
high concentrations
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of the radioactive isotope pair:
radon and thoron.
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As stress builds up in the crust right
before an earthquake,
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microfractures allow these gases
to escape to the surface.
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These scientists think that if we built
a vast network of radon-thoron detectors
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in earthquake-prone areas,
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it could become a promising
warning system–
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potentially predicting quakes
a week in advance.
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Of course,
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none of these technologies
would be as helpful
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as simply looking deep inside
the earth itself.
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With a deeper view we might be able
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to track and predict large-scale
geological changes in real time,
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possibly saving tens of thousands
of lives a year.
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But for now,
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these technologies can help us prepare
and respond quickly to areas in need–
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without waiting for directions
from a vase.
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