評論
打印
Moderator: Good morning, class. Today Professor Liu will give us a lecture about earthquakes. Welcome.
Professor Liu: 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.
In an earthquake, you might initially feel some minor trembling, then perhaps violent shaking, and then some more tremors. (16) 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.
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. (17) 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 the fastest 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.
Unlike body waves, surface waves move at or near the Earth's surface. These waves are similar to ripples on water. (18) 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. (19) 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.
16. Why do we feel different types of movement in an earthquake?
17. Why do we feel body waves only as tremors?
18. What is the most destructive type of seismic wave?
19. Which seismic wave brings us shaking felt from an earthquake?
早上好，同學們。今天劉教授會給我們講講關于地震的知識。歡迎您。
謝謝。大家都知道，有些地震震感微弱，我們在地球表面無法感知到，而另一些地震則能感到震動。當然，也可能會出現(xiàn)強烈的移動，后果往往是災難性的。出現(xiàn)地震或者巨大爆發(fā)時，我們所感受到的叫做地震波。
發(fā)生地震時，你可能最先感受到一些微弱的晃動，接著是一些強烈的顫動，然后又是一些搖晃。在地震時，人們之所以能感覺到不同類型的震動是由于有不同種類的地震波。地震波主要有兩種：體波和表面波。
你首先感受到的是體波。它們主要是在地球內(nèi)部的深處而不是表面?zhèn)鞑?span style="display:none">7b;SagR[7@^yFB@K
。有些體波傳播非常快，所以你會首先感受到它們。但是由于體波在地球深處傳播，所以人們只感覺到輕微的搖晃。體波有兩種。第一種體波是P波或者地震縱波。它是地震波里速度最快的一種。這些波能夠穿過任何物質，包括巖石和液體。正因如此，再加上它們的速度，所以縱波是第一種到達地球表面的波形。你可能聽不到感受不到這些波形，但是動物能聽到它們。它們不夠強烈，不會造成破壞。另一種體波是S波或地震橫波。因為橫波的傳播速度是縱波的一半，所以一開始你并不會感受到它們。與體波不同，表面波在地球表面或附近傳播。這些波與水面上的漣漪相似。表面波通常是破壞力最大的一種地震波，因為它的頻率更低，振幅更大，持續(xù)的時間也更長。表面波有兩種。第一種表面波是樂甫波。是表面波中速度最快的一種。另一種表面波是瑞利波。它會從地面卷過，就像波浪卷過湖泊和海洋一樣。所以它會讓地面上下左右移動，移動方向與波形傳播方向一致。地震中我們感覺到的大部分震動都是瑞利波造成的，它比其他波形更大。傳播速度比體波慢，有時候車輛會隨著瑞利波上下移動。
問題16 為什么我們會在地震中感受到不同的移動？
問題17 為什么體波只能讓人們感到輕微的搖晃？
問題18 地震波中破壞力最強的波形是什么？
問題19 地震中哪種波形會讓我們感覺到震動？
譯文屬可可原創(chuàng)，僅供學習和交流使用，未經(jīng)允許不得轉載
