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  • In 132 CE,

  • Chinese polymath Zhang Heng

  • presented the Han court with his latest invention.

  • This large vase, he claimed,

  • could tell them whenever an earthquake occurred in their kingdom

  • including the direction they should send aid.

  • The court was somewhat skeptical,

  • especially when the device triggered on a seemingly quiet afternoon.

  • But when messengers came for help days later,

  • their doubts turned to gratitude.

  • Today, we no longer rely on pots to identify seismic events,

  • but earthquakes still offer a unique challenge to those trying to track them.

  • So why are earthquakes so hard to anticipate,

  • and how could we get better at predicting them?

  • To answer that,

  • we need to understand some theories behind how earthquakes occur.

  • Earth's crust is made from several vast, jagged slabs of rock

  • called tectonic plates,

  • each riding on a hot, partially molten layer of Earth's mantle.

  • This causes the plates to spread very slowly,

  • at anywhere from 1 to 20 centimeters per year.

  • But these tiny movements are powerful enough

  • to cause deep cracks in the interacting plates.

  • And in unstable zones,

  • the intensifying pressure may ultimately trigger an earthquake.

  • It's hard enough to monitor these miniscule movements,

  • but the factors that turn shifts into seismic events are far more varied.

  • Different fault lines juxtapose different rocks

  • some of which are strongeror weakerunder pressure.

  • Diverse rocks also react differently to friction and high temperatures.

  • Some partially melt, and can release lubricating fluids

  • made of superheated minerals

  • that reduce fault line friction.

  • But some are left dry,

  • prone to dangerous build-ups of pressure.

  • And all these faults are subject to varying gravitational forces,

  • as well as the currents of hot rocks moving throughout Earth's mantle.

  • So which of these hidden variables should we be analyzing,

  • and how do they fit into our growing prediction toolkit?

  • Because some of these forces occur at largely constant rates,

  • the behavior of the plates is somewhat cyclical.

  • Today, many of our most reliable clues come from long-term forecasting,

  • related to when and where earthquakes have previously occurred.

  • At the scale of millennia,

  • this allows us to make predictions about when highly active faults,

  • like the San Andreas,

  • are overdue for a massive earthquake.

  • But due to the many variables involved,

  • this method can only predict very loose timeframes.

  • To predict more imminent events,

  • researchers have investigated the vibrations Earth elicits before a quake.

  • Geologists have long used seismometers

  • to track and map these tiny shifts in the earth's crust.

  • And today, most smartphones are also capable

  • of recording primary seismic waves.

  • With a network of phones around the globe,

  • scientists could potentially crowdsource a rich,

  • detailed warning system that alerts people to incoming quakes.

  • Unfortunately, phones might not be able to provide the advance notice needed

  • to enact safety protocols.

  • But such detailed readings would still be useful

  • for prediction tools like NASA's Quakesim software,

  • which can use a rigorous blend of geological data

  • to identify regions at risk.

  • However, recent studies indicate

  • the most telling signs of a quake might be invisible to all these sensors.

  • In 2011,

  • just before an earthquake struck the east coast of Japan,

  • nearby researchers recorded surprisingly high concentrations

  • of the radioactive isotope pair: radon and thoron.

  • As stress builds up in the crust right before an earthquake,

  • microfractures allow these gases to escape to the surface.

  • These scientists think that if we built a vast network of radon-thoron detectors

  • in earthquake-prone areas,

  • it could become a promising warning system

  • potentially predicting quakes a week in advance.

  • Of course,

  • none of these technologies would be as helpful

  • as simply looking deep inside the earth itself.

  • With a deeper view we might be able

  • to track and predict large-scale geological changes in real time,

  • possibly saving tens of thousands of lives a year.

  • But for now,

  • these technologies can help us prepare and respond quickly to areas in need

  • without waiting for directions from a vase.

In 132 CE,

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地震はなぜ予測が難しいのか?- ジャン・バティスト・コール (Why are earthquakes so hard to predict? - Jean-Baptiste P. Koehl)

  • 251 17
    April Lu に公開 2021 年 01 月 14 日
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