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The Earth’s crust—the outermost surface—is made up of large tectonic plates. As many as 20 tectonic plates cover the Earth.They move slowly, sometimes sliding under one another.Where that happens, earthquakes can take place.
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Timothy H. Dixon is with the University of South Florida.He is a geologist—a scientist who studies rocks and soil to understand the Earth.He and other scientists are using global positioning system, or GPS, equipment to measure what he calls”slow-slip”events.By that, he means slow-moving earthquakes that cannot be measured by other instruments.
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Timothy Dixon says that while such movements may not be felt, they can lead to large, sometimes deadly earthquakes.“They’re the kind of earthquake that made the big Japan earthquake in 2011 and the Sumatra earthquake and tsunami in 2004. So they can be, they can be the real killers.So what we think these slow-slip events are telling us is, they’re letting off steam, so to speak, in areas of the fault.And if they let off enough steam, that part of the fault won’t rupture.“The more of the fault that ruptures, or breaks, he says, the more powerful the earthquake is.
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The scientists set up a number of GPS receivers 15 years ago in Costa Rica to measure the”slow-slip”events, which take place only every year or two. The last one was three months before an earthquake in 2012.
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People always want to know when an earthquake is going to happen. This technology cannot predict that.But Timothy Dixon says knowing how strong the quake might be gives officials time to improve building codes and make other preparations.
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“You know the earthquake is more-or-less inevitable. Even if you don’t know exactly when it’s going to happen, since you know it’s going to happen, and you know how big it’s going to be, you can prepare accordingly.”
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A scientific paper presenting his findings was published in the Proceedings of the National Academy of Sciences.
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Ashley Thompson wrote it for VOA Learning English.December,2014
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上面一段中，各种与核心主题相关的词汇连接和与生词的搭配都出现在什么地方呢？
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●earthquakes take place strong/strength difficult to predict inevitable
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●measured by instruments global positioning system（GPS）
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●geologist studies rocks and soil slow slip fault rupture
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●earth’s crust outmost surface tectonic plates sliding under one another
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●movements be felt large deadly earthquakes tsunami
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●scientific paper presenting his findings published in
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还有几个俗语：more-or-less;letting off steam;so to speak
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最理想的学习状态，是使用多个具有同样主题内容的材料，让同样的词汇和词汇搭配以稍微不同的形式再次出现，这样会令印象更加深刻。我们再找一篇《美国地理调查》网站上的地震灾害项目专题，其中有很多对儿童和青少年进行科普的文章。比如下面这篇文章：
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The Science of Earthquakes
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What is an earthquake?
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An earthquake is what happens when two blocks of the earth suddenly slip past one another. The surface where they slip is called the fault or fault plane.Thelocation below the earth’s surface where the earthquake starts is called the hypocenter, and the location directly above it on the surface of the earth is called the epicenter.
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Sometimes an earthquake has foreshocks. These are smaller earthquakes that happen in the same place as the larger earthquake that follows.Scientists can’t tell that an earthquake is a foreshock until the larger earthquake happens.The largest, main earthquake is called the mainshock.Mainshocks always have aftershocks that follow.These are smaller earthquakes that occur afterwards in the same place as the mainshock.Depending on the size of the mainshock, aftershocks can continue for weeks, months, and even years after the mainshock！
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The earth has four major layers：the inner core, outer core, mantle and crust. The crust and the top of the mantle make up a thin skin on the surface of our planet.But this skin is not all in one piece—it is made up of many pieces like a puzzle covering the surface of the earth.Not only that, but these puzzle pieces keep slowly moving around, sliding past one another and bumping into each other.We call these puzzle pieces tectonic plates, and the edges of the plates are called the plate boundaries.The plate boundaries are made up of many faults, and most of the earthquakes around the world occur on these faults.Since the edges of the plates are rough, they get stuck while the rest of the plate keeps moving.Finally, when the plate has moved far enough, the edges unstick on one of the faults and there is an earthquake.
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While the edges of faults are stuck together, and the rest of the block is moving, the energy that would normally cause the blocks to slide past one another is being stored up. When the force of the moving blocks finally overcomes the friction of the jagged edges of the fault and it unsticks, all that stored up energy is released.The energy radiates outward from the fault in all directions in the form of seismic waves like ripples on a pond.The seismic waves shake the earth as they move through it, and when the waves reach the earth’s surface, they shake the ground and anything on it, like our houses and us！
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