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  • Hi, this is Alex, from MinuteEarth.

  • San Francisco has been hit by a big earthquake at least once every hundred years going back

  • as far as we know.

  • So the people of San Francisco know that sometime in the next 100 years, theyre likely to

  • get shaken again by a big quake.

  • But we can't say exactly when the quake might hit.

  • Right now, all we can do is construct shake-proof buildings and put out seismic sensors.

  • That way, when an earthquake sends out underground waves, which travel from its epicenter eight

  • times faster than the destructive surface waves, we can detect the underground waves

  • with enough time to give a warning like: “Uh oh!

  • An earthquake is about to hit us!”... which is, surprisingly, enough time to turn off

  • gas pipelines and stop trains and find cover, but it doesn’t help people get out of town.

  • For people to evacuate safely from natural disasters, it’s not helpful to give a really

  • short warning, or a really big window within which a disaster might happen.

  • According to disaster experts, 2 days is juust right.

  • But if we want to be able to be predict earthquakes with that amount of precision, we need to

  • understand a LOT more about how they work.

  • Weve tried looking backwards at quakes that have already happened, and identifying

  • events that occurred in the days before they hit, like multiple mini-quakes, big releases

  • in radon gas, changes in magnetism, and even weird animal behavior, to see if any of these

  • were predictors of an impending quake.

  • But lots of times these things happen without accompanying earthquakes, and lots of times

  • earthquakes happen without these things, so, so far we haven't been able to find any reliable

  • predictors.

  • Another approach is to build an accurate model of the earth beneath our feet: we know that

  • over time, as tectonic plates rub against each other, the stress that builds up is sometimes

  • violently released as an earthquake.

  • If we had a really good model and reliable measurements of the forces on the plates,

  • maybe then we could predict when and where an earthquake was going to happen.

  • But plates are often more than 15 miles thick.

  • That’s twice as deep as humans have ever dug, so it would be pretty difficult to get

  • monitoring equipment deep enough.

  • So, were creating mini-faults in the lab, to better understand the forces on moving

  • plates, and to help identify reliable ways to measure the forces from the surface of

  • the earth.

  • But in order to test our models, we need to be able to compare them to actual gigantic

  • earthquakes, which, as we mentioned, don't happen that often.

  • Luckily for researchers, a few ocean faults are more productive, and frequently cause

  • large but relatively harmless quakes, giving us a regular way to calibrate and fine tune

  • our models.

  • One big thing theyve helped us learn is that the interactions between fault segments

  • are really important: for example, when this particular segment slips, it increases the

  • chances its neighbor will slip, letting us predict where the next quake will happen.

  • In some faults, we can even say that itll happen within a couple of years.

  • Compared to a hundred year window, that’s really precise, but there are still two big

  • problems.

  • First, these ocean faults are relatively simple, so we still have to figure out how to apply

  • what weve learned from them to more complicated faults, like the ones near San Francisco.

  • And second, even if we could do that, we’d still be a long way away from the ideal two-day

  • notice.

  • And unfortunately, our existing methods probably aren’t going to help us get there.

  • What we need is an earth-shattering breakthrough.

  • Thanks to the University of Rhode Island for sponsoring this video, which was made possible

  • by a National Science Foundation grant to Matt Wei, a professor in URI’s Graduate

  • School of Oceanography.

  • Dr. Wei uses seismic data and simulations to study the physics of plate tectonics and

  • earthquakes.

  • His research on fast spreading oceanic transform faults - like the Discovery fault in the East

  • Pacific - has helped us start to understand the importance of earthquake cycles as we

  • work to crack the code of earthquake physics.

  • Thanks University of Rhode Island.

Hi, this is Alex, from MinuteEarth.

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為什麼地震如此難以預測? (Why Earthquakes Are So Hard To Predict)

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    林宜悉 發佈於 2021 年 01 月 14 日
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