Why are earthquakes so hard to predict? - Jean-Baptiste P. Koehl

譯者: Lilian Chiu 審譯者: SF Huang

In 132 CE,

公元 132 年，

Chinese polymath Zhang Heng

中國博學家張衡

presented the Han court with his latest invention.

將他最新的發明上呈給東漢朝廷。

This large vase, he claimed,

他宣稱這個大型的瓶狀物

could tell them whenever an earthquake occurred in their kingdom–

可以預測國境內何時會發生地震——

including the direction they should send aid.

還會指引他們要往何處去救援。

The court was somewhat skeptical,

朝廷有點存疑，

especially when the device triggered on a seemingly quiet afternoon.

特別是當這個裝置在一個 看似很寧靜的午後被觸動了。

But when messengers came for help days later,

但，當數日後使者前來尋求協助時，

their doubts turned to gratitude.

他們的態度從懷疑變成感激。

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

現今，我們不再依靠瓶子來識別地震，

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

但對於試圖追蹤地震的人來說， 地震仍然是個很獨特的挑戰。

So why are earthquakes so hard to anticipate,

為什麼地震這麼難以預測？

and how could we get better at predicting them?

我們要如何才能預測得更好？

To answer that,

要回答這問題，我們就得了解

we need to understand some theories behind how earthquakes occur.

一些關於地震發生的理論。

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

地球的地殼是由數個 鋸齒狀的大型岩石組成，

called tectonic plates,

這些岩石叫做板塊，

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

每個板塊都漂浮在一層 高溫且部分熔化的地幔上。

This causes the plates to spread very slowly,

這會使板塊緩緩散開，

at anywhere from 1 to 20 centimeters per year.

速度大約是每年 1~20 公分。

But these tiny movements are powerful enough

但這些微小的移動強大到

to cause deep cracks in the interacting plates.

足以造成相互影響的板塊破裂。

And in unstable zones,

在不穩定的區域，

the intensifying pressure may ultimately trigger an earthquake.

越來越高的壓力最終會觸發地震。

It’s hard enough to monitor these miniscule movements,

要監視這些微小的移動 就已經夠難了，

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

板塊移動進而造成地震的因素 又更是多樣化。

Different fault lines juxtapose different rocks–

不同的斷層線讓不同的岩石並列——

some of which are stronger–or weaker– under pressure.

在壓力之下，有的岩石較強， 有岩石的較弱，

Diverse rocks also react differently to friction and high temperatures.

各種岩石對於磨擦 和高溫的反應也不一樣。

Some partially melt, and can release lubricating fluids

有些會部分熔化， 釋出具滑潤作用的液體，

made of superheated minerals

其成份是過熱的礦物，

that reduce fault line friction.

這種液體會減少斷層線的摩擦。

But some are left dry,

但有一些則是乾燥的，

prone to dangerous build-ups of pressure.

當壓力越來越高時就可能很危險。

And all these faults are subject to varying gravitational forces,

所有這些斷層都會 受到不同重力的影響，

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

如同熱岩石在地球地幔上的 移動也會影響到斷層。

So which of these hidden variables should we be analyzing,

所以，我們該分析哪些隱藏的變數？

and how do they fit into our growing prediction toolkit?

我們又該如何將它們 與發展中的預測工具相結合？

Because some of these forces occur at largely constant rates,

因為這些影響力當中， 有一些發生的頻率很高，

the behavior of the plates is somewhat cyclical.

板塊的行為像是具有週期性。

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

現今，我們最可靠的線索 多半是來自長期預測，

related to when and where earthquakes have previously occurred.

從過往地震事件的 時間和地點資料來推導。

At the scale of millennia,

以千年的長度來看，

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

我們就能夠預測那些活躍的斷層——

like the San Andreas,

像聖安地列斯斷層——

are overdue for a massive earthquake.

已經超過預期的地震週期了。

But due to the many variables involved,

但因為涉及太多變數，

this method can only predict very loose timeframes.

這個方法只能預測出 很寬鬆的時間範圍。

To predict more imminent events,

為了預測近期的地震，

researchers have investigated the vibrations Earth elicits before a quake.

研究者已經探究過在地震發生前 地球所引起的震動。

Geologists have long used seismometers

地質學家長期都在使用地震儀

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

來追蹤地殼中的微小移動 並將它們繪製在圖上。

And today, most smartphones are also capable

現今，大部分的智慧手機都能夠

of recording primary seismic waves.

記錄主要的地震波。

With a network of phones around the globe,

有了全球的手機網，

scientists could potentially crowdsource a rich,

科學家就有可能以群眾外包的方式，

detailed warning system that alerts people to incoming quakes.

做出有豐富細節資訊的警報系統， 來警告大家即將發生的地震。

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

不幸的是，手機可能 無法事先提供大家所需的

to enact safety protocols.

臨震安全應變措施。

But such detailed readings would still be useful

但這些細節的讀數仍然很有用，

for prediction tools like NASA’s Quakesim software,

可以用在像美國太空總署的 Quakesim 軟體等預測工具上，

which can use a rigorous blend of geological data

它可以將地質資料做精確的結合，

to identify regions at risk.

來找出有風險的地區。

However, recent studies indicate

然而，近期的研究指出，

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

這些感測器可能無法抓到 清楚的地震徵兆。

In 2011,

2011 年，

just before an earthquake struck the east coast of Japan,

就在地震襲擊日本東岸之前，

nearby researchers recorded surprisingly high concentrations

附近的研究者記錄到 成對的放射性同位素：

of the radioactive isotope pair: radon and thoron.

氡和釷射氣的濃度高得嚇人。

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

地震前隨著地殼中的壓力不斷升高，

microfractures allow these gases to escape to the surface.

微小的破裂處讓這些氣體 跑到地球表面。

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

這些科學家認為如果我們能在 經常發生地震的區域，

建立氡—釷射氣的大型偵測器網絡，

in earthquake-prone areas,

it could become a promising warning system–

就可能做出理想的警告系統——

potentially predicting quakes a week in advance.

在地震發生前一週就能預測得到。

Of course,

當然，這些技術再有幫助，

none of these technologies would be as helpful

as simply looking deep inside the earth itself.

都不如直接地去看地球的深處。

With a deeper view we might be able

若能看得更深，我們可能可以

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

即時追蹤並預測大規模的地質變動，

possibly saving tens of thousands of lives a year.

每年可能可以拯救數萬人的性命。

But for now,

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

但，目前這些技術 能協助我們做好準備，

並針對有需求的區域做出快速應變——

without waiting for directions from a vase.

不用再等著一個瓶子來指示我們。