[越毒] 肆月贰日越毒寂静皮皮整理（共47只，更新4/27 22:39）

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27*. 地震理论
GWD24-passage four深层地震的成因探析

In most earthquakes the Earth’s crust cracks like porcelain. Stress builds up until a fracture forms at a depth of a few kilometers and the crust slips to relieve the stress. Some earthquakes, however, take place hundreds of kilometers down in the Earth’s mantle, where high pressure makes rock so ductile that it flows instead of cracking, even under stress severe enough to deform it like putty. How can there be earthquakes at such depths?
That such deep events do occur has been accepted only since 1927, when the seismologist Kiyoo Wadati convincingly demonstrated their existence. Instead of comparing the arrival times of seismic waves at different locations, as earlier researchers had done, Wadati relied on a time difference between the arrival of primary (P) waves and the slower secondary (S) waves. Because P and S waves travel at different but fairly constant speeds, the interval between their arrivals increases in proportion to the distance from the earthquake focus, or initial rupture point. For most earthquakes, Wadati discovered, the interval was quite short near the epicenter; the point on the surface where shaking is strongest. For a few events, however, the delay was long even at the epicenter. Wadati saw a similar pattern when he analyzed data on the intensity of shaking. Most earthquakes had a small area of intense shaking, which weakened rapidly with increasing distance from the epicenter, but others were characterized by a lower peak intensity, felt over a broader area. Both the P-S intervals and the intensity patterns suggested two kinds of earthquakes: the more (45) common shallow events, in which the focus lay just under the epicenter, and deep events, with focus several hundred kilometers down.
The question remained: how can such quakes occur, given that mantle rock at a depth of more than 50 kilometers is too ductile to store enough stress to fracture? Wadati’s work suggested that deep events occur in areas (now called Wadati-Benioff zones), where one crustal plate is forced under another and descends into the mantle. The descending rock is substantially cooler than the surrounding mantle and hence is less ductile and much more liable to fracture.
本文体会通篇的对比。
在大多数地震里，地壳瓷般碎裂。压力聚集，直到破裂在数公里深处形成，地壳滑动以释放压力。但是有些地震在数百公里深的地幔发生，虽然在那里压力巨大，岩石变得柔软，浮动而不破裂。这种地震如何发生？
深层地震到了1927年才被接受为事实。前人通常比较不同地点震波的到达时间，而KW则比较P波和S波到达时间的差别。因为P波和S波以不同的连续速度行进，它们到达的间隔随震源距离成比例增长。KW发现，在震中（地表摇得最厉害的地方）附近的间隔较短，但是某些情况下，即使在震中附近间隔也很长。振动密度数据也呈类似结果。大多数地震有一个密集振动的范围，振动随震中距离加大而迅速减少，但是另外一种地震的特点是更广范围更低峰值的强度。P-S间隔和强度类型都暗示了两种地震：更常见的浅层地震，震源在震中下面；还有深层地震，震源在数百公里深处。
问题持续：什么导致了深层地震，既然地幔软得不足以存储压力？KW的实验显示，深层地震出现在一块地壳板块被另一块挤向下方地幔之处。下降的岩石比周围地幔冷一些，所以不那么软，更容易碎裂。

24-30 The author’s explanation of how deep events occur would be most weakened if which of the following were discovered to be true?
A) Deep events are far less common than shallow events.
B) Deep events occur in places other than where crustal plates meet.
Wadati’s work suggested that deep events occur in areas (now called Wadati-Benioff zones), where one crustal plate is forced under another and descends into the mantle.
C) Mantle rock is more ductile at a depth of several hundred kilometers than it is at 50 kilometers.
D) The speeds of both P and S waves are slightly greater than previously thought.
E) Below 650 kilometers earthquakes cease to occur.

24-31 Information presented in the passage suggests that, compared with seismic activity at the epicenter of a shallow event, seismic activity at the epicenter of a deep event is characterized by
A) shorter P-S intervals and higher peak intensity
B) shorter P-S intervals and lower peak intensity
C) longer P-S intervals and similar peak intensity
D) longer P-S intervals and higher peak intensity
E) longer P-S intervals and lower peak intensity
For most earthquakes, Wadati discovered, the interval was quite short near the epicenter; the point on the surface where shaking is strongest.将其取非即可

24-32 The passage supports which of the following statements about the relationship between the epicenter and the focus of an earthquake?
A) P waves originate at the focus and S waves originate at the epicenter.
B) In deep events the epicenter and the focus are reversed.
C) In shallow events the epicenter and the focus coincide
D) In both deep and shallow events the focus lies beneath the epicenter
E) The epicenter is in the crust, whereas the focus is in the mantle.
the more (45) common shallow events, in which the focus lay just under the epicenter, and deep events, with focus several hundred kilometers down.

24-33 The passage suggests that which of the following must take place in order for any earthquake to occur?
I. Stress must build up
II. Cool rock must descend into the mantle.
III. A fracture must occur.
I only
II only
III only
I and III only
I, II and III

songci88

灰常灰常灰常的感谢~~

邵軼

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邵軼

怎么打开word在word里链接呀

rahel

楼主我爱你！！谢谢亲~~~辛苦了，感谢各位同学无私奉献！

rahel

楼主我爱你！！谢谢亲~~~辛苦了，感谢各位同学无私奉献！

lol31

谢谢！！5月3号考的飘过

shinydo

ls辛苦啦~~大谢！！求问 目录蓝色的字后面的数字表示出现次数还是神马？？

serendipe2

辛苦了

iris潇

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