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Good morning, class. Today Professor Liu will give us a lecture about earthquakes. Welcome.
早上好，同学们。今天刘教授会给我们讲讲关于地震的知识。欢迎您。
Thank you. As you know, some earthquakes are not powerful enough to be felt on the Earth's surface while in others, people can, indeed, feel the earth shaking. And of course, there might be violent movement, often with catastrophic results. What we feel during an earthquake or huge explosion are a series of waves called seismic waves.
谢谢。大家都知道，有些地震震感微弱，我们在地球表面无法感知到，而另一些地震则能感到震动。当然，也可能会出现强烈的移动，后果往往是灾难性的。出现地震或者巨大爆发时，我们所感受到的叫做地震波。
In an earthquake, you might initially feel some minor trembling, then perhaps violent shaking, and then some more tremors. The reason why you feel these different types of movement is because there are different kinds of seismic waves. There are two major types of seismic waves: body waves and surface waves.
发生地震时，你可能最先感受到一些微弱的晃动，接着是一些强烈的颤动，然后又是一些摇晃。在地震时，人们之所以能感觉到不同类型的震动是由于有不同种类的地震波。地震波主要有两种：体波和表面波。
The waves that you feel first are body waves. These mainly travel deep through the Earth's interior rather than at the surface. Some of them travel very fast, and that's why you feel them first. But because they travel deep inside the Earth, they're felt only as tremors. There are two types of body waves. The first type of body wave is the P wave or primary wave. It's thefastest kind of seismic wave. These waves can move through any type of material, including rock and fluids. Because of this and because of their speed, these waves are the first to reach the Earth's surface. You likely won't even hear or feel these waves, but animals may hear them. They're not strong enough to cause significant damage. The other type of body wave is the S wave or secondary wave. Because S waves travel at half the speed of P waves, you won't feel them in the beginning.
你首先感受到的是体波。它们主要是在地球内部的深处而不是表面传播。有些体波传播非常快，所以你会首先感受到它们。但是由于体波在地球深处传播，所以人们只感觉到轻微的摇晃。体波有两种。第一种体波是P波或者地震纵波。它是地震波里速度最快的一种。这些波能够穿过任何物质，包括岩石和液体。正因如此，再加上它们的速度，所以纵波是第一种到达地球表面的波形。你可能听不到感受不到这些波形，但是动物能听到它们。它们不够强烈，不会造成破坏。另一种体波是S波或地震横波。因为横波的传播速度是纵波的一半，所以一开始你并不会感受到它们。
Unlike body waves, surface waves move at or near the Earth's surface. These waves are similar to ripples on water. They are usually the most destructive type of seismic wave because of their lower frequency, larger amplitude, and longer duration. There are two types of surface waves. The first kind of surface wave is called a love wave. It's the fastest surface wave. The other kind of surface wave is the Rayleigh wave. It rolls along the ground just like a wave rolls across a lake or an ocean. As a result, it moves the ground up and down and side to side in the same direction that the wave is moving. Most of the shaking felt from an earthquake is due to the Rayleigh wave, which can be much larger than the other waves. They are slower than body waves, and sometimes cars might appear to be moving up and down with these waves.
与体波不同，表面波在地球表面或附近传播。这些波与水面上的涟漪相似。表面波通常是破坏力最大的一种地震波，因为它的频率更低，振幅更大，持续的时间也更长。表面波有两种。第一种表面波是乐甫波。是表面波中速度最快的一种。另一种表面波是瑞利波。它会从地面卷过，就像波浪卷过湖泊和海洋一样。所以它会让地面上下左右移动，移动方向与波形传播方向一致。地震中我们感觉到的大部分震动都是瑞利波造成的，它比其他波形更大。传播速度比体波慢，有时候车辆会随着瑞利波上下移动。
Question 16. Why do we feel different types of movement in an earthquake?
问题16 为什么我们会在地震中感受到不同的移动？
Question 17. Why do we feel body waves only as tremors?
问题17 为什么体波只能让人们感到轻微的摇晃？
Question 18. What is the most destructive type of seismic wave?
问题18 地震波中破坏力最强的波形是什么？
Question 19. Which seismic wave brings us shaking felt from an earthquake?
问题19 地震中哪种波形会让我们感觉到震动？
