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Earthquakes

An earthquake is one of the most terrifying phenomena that nature can dish up. We generally think of the ground we stand on as “rock-solid” and completely stable. An earthquake can shatter（粉碎）that perception instantly, and often with extreme violence.

Up until relatively recently, scientists only had unsubstantiated（无确实根据的）guesses as to what actually caused earthquakes. Even today there is still a certain amount of mystery surrounding them, but scientists have a much clearer understanding.

There has been enormous progress in the past century: Scientists have identified the forces that cause earthquakes, and developed technology that can tell us an earthquake's magnitude and origin. The next hurdle is to find a way of predicting earthquakes, so they don't catch people by surprise.

In this article, we'll find out what causes earthquakes, and we'll also find out why they can have such a devastating effect on us.

Shaking Ground

An earthquake is a vibration（震动）that travels through the earth's crust. Technically, a large truck that rumbles down the street is causing a mini-earthquake, if you feel your house shaking as it goes by; but we tend to think of earthquakes as events that affect a fairly large area, such as an entire city. All kinds of things can cause earthquakes:

volcanic eruptions

meteor impacts

underground explosions (an underground nuclear test, for example)

collapsing structures (such as a collapsing mine)

But the majority of naturally-occurring earthquakes are caused by movements of the earth's plates.

We only hear about earthquakes in the news every once in a while, but they are actually an everyday occurrence on our planet. According to the United States Geological Survey, more than 3 million earthquakes occur every year. That's about 8,000 a day, or one every 11 seconds!

The vast majority of these 3 million quakes are extremely weak. The law of probability also causes a good number of stronger quakes to happen in uninhabited places where no one feels them. It is the big quakes that occur in highly populated areas that get our attention.

Earthquakes have caused a great deal of property damage over the years, and they have claimed many lives. In the last hundred years alone, there have been more than 1.5 million earthquake-related fatalities. Usually, it's not the shaking ground itself that claims lives; it's the associated destruction of manmade structures and the instigation（发起）of other natural disasters, such as tsunamis, avalanches（雪崩）and landslides.

Sliding Plates

The biggest scientific breakthrough in the history of seismology—the study of earthquakes—came in the middle of the 20th century, with the development of the theory of plate tectonics（筑造学）. Scientists proposed the idea of plate tectonics to explain a number of peculiar phenomena on earth, such as the apparent movement of continents over time, the clustering of volcanic activity in certain areas and the presence of huge ridges at the bottom of the ocean.

The basic theory is that the surface layer of the earth—the lithosphere—is comprised of many plates that slide over the lubricating（润滑的）athenosphere layer. At the boundaries between these huge plates of soil and rock, three different things can happen:

●　Plates can move apart. If two plates are moving apart from each other, hot, molten rock flows up from the layers of mantle below the lithosphere. This magma（岩浆）comes out on the surface (mostly at the bottom of the ocean), where it is called lava（熔岩）. As the lava cools, it hardens to form new lithosphere material, filling in the gap. This is called a divergent plate boundary.

●　Plates can push together. If the two plates are moving toward each other, one plate typically pushes under the other one. This sub-ducting plate sinks into the lower mantle layers, where it melts. At some boundaries where two plates meet, neither plate is in a position to sub-duct under the other, so they both push against each other to form mountains. The lines where plates push toward each other are called convergent plate boundaries.

●　Plates slide against each other. At other boundaries, plates simply slide by each other—one moves north and one moves south, for example. While the plates don't drift directly into each other at these transform boundaries, they are pushed tightly together. A great deal of tension builds at the boundary.

Dealing with Earthquakes

We understand earthquakes a lot better than we did even 50 years ago, but we still can't do much about them. They are caused by fundamental, powerful geological processes that are far beyond our control. These processes are also fairly unpredictable, so it's not possible at this time to tell people exactly when an earthquake is going to occur. The first detected seismic waves will tell us that more powerful vibrations are on their way, but this only gives us a few minutes' warning, at most.

So what can we do about earthquakes? The major advances over the past 50 years have been in preparedness, particularly in the field of construction engineering. In 1973, the Uniform Building Code, an international set of standards for building construction, added specifications to fortify buildings against the force of seismic waves. This includes strengthening support material as well as designing buildings so they are flexible enough to absorb vibrations without falling or deteriorating. It's very important to design structures that can take this sort of punch, particularly in earthquake-prone areas.

Another component of preparedness is educating the public. The United States Geological Survey (USGS) and other government agencies have produced several brochures explaining the processes involved in an earthquake and giving instructions on how to prepare your house for a possible earthquake, as well as what to do when a quake hits.

In the future, improvements in prediction and preparedness should further minimize the loss of life and property associated with earthquakes. But it will be a long time, if ever, before we'll be ready for every substantial earthquake that might occur. Just like severe weather and disease, earthquakes are an unavoidable force generated by the powerful natural processes that shape our planet. All we can do is increase our understanding of the phenomenon and develop better ways to deal with it.

1. Scientists had unsubstantiated guesses as to _____ up until relatively recently.

A. when actually earthquakes happened

B. what actually caused earthquakes

C. how earthquakes happened

D. where actually earthquakes happened

2. What is an earthquake?

A. An earthquake is the most terrifying phenomena that nature can present to human beings.

B. An earthquake can shatter our world instantly, and often with extreme violence.

C. An earthquake is a vibration that travels through the earth's core.

D. An earthquake is a vibration that travels through the earth's crust.

3. The majority of naturally-occurring earthquakes are caused by _____.

A. volcanic eruptions

B. meteor impacts

C. collapsing structures

D. movements of the earth's plates

4. How many earthquakes occur every day according to the United States Geological Survey?

A. More than 3 million.

B. 1.5 million.

C. About 8,000.

D. 11.

5. Scientists proposed the idea of plate tectonics to explain _____.

A. a number of peculiar phenomena on earth

B. a number of regular phenomena on earth

C. the clustering of volcanic activity in uncertain areas

D. the presence of huge ridges at the top of the ocean

6. The surface layer of the earth is the lithosphere, which is comprised of many plates that slide over _____.

A. the presence of huge ridges

B. the lubricating athenosphere layer

C. the new lithosphere material

D. the clustering of volcanic activity

7. What will happen if two plates are moving apart from each other?

A. One plate typically pulls the other one.

B. One plate typically pushes under the other one.

C. The convergent plate boundaries will be formed.

D. Hot, molten rock flows up from the layers of mantle below the lithosphere.

8. The convergent plate boundaries refer to the lines where plates _____.

9. The major advances over the past 50 years have been in preparedness, particularly in the field of construction engineering and _____.

10. In the future, improvements in prediction and preparedness should further minimize the loss of _____ associated with earthquakes.

文章精要：

地震危害巨大，了解地震对减少其带来的损失有着重要意义。本文讲解了引发地震的因素、与地震有关的地壳板块运动和地震的危害，并指出尽管人类还无法准确预测地震，但一些必要的防御措施能够减少地震带来的损失。

答案解析：

1. B　根据题干中的信息词Scientists had unsubstantiated guesses和up until relatively recently定位到原文第二段首句，可知直到最近，科学家对引发地震的原因也只停留在无确实根据的猜测上，故本题选B。

2. D　题干问的是地震是什么，即对地震的定义，根据原文第一个小标题下的首句，可知地震是穿行于地壳的震动，故本题选D。

3. D　根据题干中的信息词The majority of和naturally-occurring earthquakes定位到原文第一个小标题下的第二段，可知大部分自然发生的地震都是由地球板块运动引起的，而并不是由火山爆发等其他因素引起的，故本题选D。

4. C　根据题干中的信息词earthquakes occur every day和United States Geological Survey定位到原文第一个小标题下的第三段，可知根据美国地质局的监测，每年会发生超过300万次的地震，也就是每天大约8000次，每秒钟大约11次，故本题选C。

5. A　根据题干中的信息词Scientists proposed和the idea of plate tectonics定位到原文第二个小标题下的第一段第二句，可知科学家提出板块建筑学的观点来解释地球上许多奇特的现象，故本题选A。

6. B　根据题干中的信息词The surface layer of the earth和lithosphere定位到原文第二个小标题下的第二段首句，可知地球的表层，即岩石圈，是由许多在润滑的软流圈上滑动的板块构成的，故本题选B。

7. D　根据题干中的信息词if two plates和moving apart定位到原文第二个小标题下的第二段第一点的第二句，可知如果两个板块向脱离彼此的方向运动，热的、溶化的岩石就会流向岩石圈的下面，故本题选D。

8. push toward each other/push together。根据题干中的信息词convergent plate boundaries定位到原文第二个小标题下第二点的最后，可知板块相互推挤的边界被称为聚合板块边界，由此可得答案。该点开始提到板块可以推挤到一起，指的就是板块相互推挤，故此处还可填push together。

9. educating the public。根据题干中的信息词major advances和past 50 years定位到原文最后一个小标题下的第二段，可知过去50年间主要的进步在于防御，下一段又提到防御的另一组成部分就是教育公众。

10. life and property。根据题干中的信息词improvements in prediction and preparedness定位到原文最后一段的首句，可知今后预测和防御的进步将进一步将与地震相关的人员和财产损失降低到最小的程度，由此可得答案。