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In 132 CE,

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Chinese polymath Zhang Heng

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presented the Han court with [br]his latest invention.

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This large vase, he claimed,

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could tell them whenever an earthquake [br]occurred in their kingdom–

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including the direction [br]they should send aid.

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The court was somewhat skeptical,

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especially when the device triggered [br]on a seemingly quiet afternoon.

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But when messengers came [br]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 [br]identify seismic events,

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but earthquakes still offer a unique[br]challenge to those trying to track them.

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So why are earthquakes so [br]hard to anticipate,

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and how could we get better [br]at predicting them?

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To answer that,

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we need to understand some theories [br]behind how earthquakes occur.

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Earth’s crust is made from several vast, [br]jagged slabs of rock

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called tectonic plates,

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each riding on a hot, partially molten[br]layer of Earth’s mantle.

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This causes the plates to [br]spread very slowly,

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at anywhere from 1 to 20 [br]centimeters per year.

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But these tiny movements are powerful [br]enough

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to cause deep cracks in the[br]interacting plates.

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And in unstable zones,

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the intensifying pressure may [br]ultimately trigger an earthquake.

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It’s hard enough to monitor these [br]miniscule movements,

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but the factors that turn shifts into [br]seismic events are far more varied.

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Different fault lines juxtapose [br]different rocks–

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some of which are stronger–or weaker–[br]under pressure.

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Diverse rocks also react differently to[br]friction and high temperatures.

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Some partially melt, and can release[br]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 [br]varying gravitational forces,

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as well as the currents of hot rocks[br]moving throughout Earth’s mantle.

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So which of these hidden variables [br]should we be analyzing,

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and how do they fit into our [br]growing prediction toolkit?

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Because some of these forces occur [br]at largely constant rates,

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the behavior of the plates [br]is somewhat cyclical.

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Today, many of our most reliable clues [br]come from long-term forecasting,

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related to when and where earthquakes [br]have previously occurred.

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At the scale of millennia,

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this allows us to make predictions [br]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 [br]very loose timeframes.

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To predict more imminent events,

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researchers have investigated the [br]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[br]in the earth’s crust.

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And today, most smartphones are [br]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 [br]crowd source a rich,

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detailed warning system that alerts [br]people to incoming quakes.

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Unfortunately, phones might not be able[br]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 [br]useful

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for prediction tools like NASA’s [br]Quakesim software,

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which can use a rigorous blend of [br]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[br]invisible to all these sensors.

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In 2011,

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just before an earthquake struck [br]the east coast of Japan,

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nearby researchers recorded surprisingly [br]high concentrations

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of the radioactive isotope pair [br]radon and thoron.

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As stress builds up in the crust right [br]before an earthquake,

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microfractures allow these gases [br]to escape to the surface.

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These scientists think that if we built [br]a vast network of radon-thoron detectors

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in earthquake-prone areas,

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it could become a promising [br]warning system–

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potentially predicting quakes [br]a week in advance.

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Of course,

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none of these technologies [br]would be as helpful

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as simply looking deep inside [br]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 [br]geological changes in real time,

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possibly saving tens of thousands [br]of lives a year.

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But for now,

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these technologies can help us prepare [br]and respond quickly to areas in need–

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without waiting for directions [br]from a vase.