gwd-24-30，31求教

Maggieyin

24-passage three

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.

问题依然存在，假定在50千米一下构成地幔的岩石很有韧性，不会蓄积足够大的应力发生断裂，为什么这样的深层地震还会发生呢？W的理论解释说，在发生地震的区域，地壳板块相互挤压，向地幔下陷。下陷的板块比周围的板块温度低很多，因此，不再柔韧而容易断裂。

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.

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

不明白为什么选的答案，我的翻译对不对？请指点！

xealot

24-30:

According to the Wadati's explanation, the "deep event" occurs in areas where "one crustal plate is forced under another". This is what the explanation is based on. If B is true, such conclusion comes to groundless. And, the author apparently agrees with Wadati's position regarding this problem.

24-31:

First of all, we got "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." That is, the farther the rupture occurs, the longer P-S interval;

Secondly, we got "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. " That is to say, that most earthquakes occur near the epicenter, and that only a few has a long delay. For the first point, we can see that such "a few" cases are the deeper ones.

Finally, we got "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. " According to this, the cases rather than the "most earthquakes" could be characterized by "a lower intensity".

So we can quickly draw the final conclusion.

我是一条鱼

NX

PFPF

GMAT阿驴

以下是引用Maggieyin在2005-1-15 6:20:00的发言：

24-passage three

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.

问题依然存在，假定在50千米一下构成地幔的岩石很有韧性，不会蓄积足够大的应力发生断裂，为什么这样的深层地震还会发生呢？W的理论解释说，在发生地震的区域，地壳板块相互挤压，向地幔下陷。下陷的板块比周围的板块温度低很多，因此，不再柔韧而容易断裂。

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.

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

不明白为什么选的答案，我的翻译对不对？请指点！

31 CHOOSE E  定位在画线部分

阿土莎莎

vv_mind

还是不明白，30题我找的定位点是最后一句：

The descending rock is substantially cooler than the surrounding mantle and hence is less ductile and much more liable to fracture.

所以我选了C

被大家说的定位点，我觉得B是对的，但我同时觉得C好像也没错呀。

像c说的，如果地幔下的岩石很容易断裂的话，那也不会有earthquake了呀。

是不是我理解错了哪句话的意思？  请NN指点  

Shiry

不是NN ，不过发表点自己的看法 我本来也是选C的 现在回头看看觉得有点问题

C.      Mantle rock is more ductile at a depth of several hundred kilometers than it is at 50 kilometers.

原文：

    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.

整篇文章只在这里提到提到50 kilometers 其他的地方并没有涉及更谈不上有比较，小安阅读法里面说，细节题主要就是取非和关键字替换，所以从原文推不出C选项。

[此贴子已经被作者于2008-5-25 10:24:18编辑过]

hhdty

我这个问题和答案没有看懂，谁可以帮忙翻译一下。谢谢

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.

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.

Norgar

以下是引用vv_mind在2008/1/26 18:54:00的发言：

还是不明白，30题我找的定位点是最后一句：

The descending rock is substantially cooler than the surrounding mantle and hence is less ductile and much more liable to fracture.

所以我选了C

被大家说的定位点，我觉得B是对的，但我同时觉得C好像也没错呀。

像c说的，如果地幔下的岩石很容易断裂的话，那也不会有earthquake了呀。

是不是我理解错了哪句话的意思？  请NN指点  

原文说的是descending rock和surrounding mantle比较less ductile,而C选项是拿 deep mantle rock和surface mantle rock比,比较的不是一回事,因此起不到削弱作用.

paopao20

还是不明白，30题我找的定位点是最后一句：
The descending rock is substantially cooler than the surrounding mantle and hence is less ductile and much more liable to fracture.
所以我选了C
被大家说的定位点，我觉得B是对的，但我同时觉得C好像也没错呀。
像c说的，如果地幔下的岩石很容易断裂的话，那也不会有earthquake了呀。
是不是我理解错了哪句话的意思？  请NN指点  

-- by 会员 vv_mind (2008/1/26 18:54:00)

c 里面这一点在板块交界的地方也符合的，就是说这是个general的情况。而Wadati找出的原因是在板块交界的地带balabala...如果能找到不是板块交界的那么deep的地方也发生地震就能weaken（B）