返回列表 发帖

大全79,主题题型

Passage 79 (16/22)

In most earthquakes the Earth’s crust cracks like porcelain. Stress builds up (build up: v.树立, 增进, 增大) 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 (in proportion t adv....成比例) the distance from the earthquake focus (earthquake focus: 震源), or rupture point.

For most earthquakes, Wadati discovered, the interval was quite short near the epicenter (epicenter: n.震中, 中心), 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 common shallow events, in which the focus lay just under the epicenter, and deep events, with a focus several hundred kilometers down.

The question remained: how can such quakes occur, given (in view of (in view of: adv.考虑到, 由于): CONSIDERING “given what she knew about others' lives, how could she complain about her own? Marilyn F.”) 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.

1. The passage is primarily concerned with

(A) demonstrating why the methods of early seismologists were flawed

(B) arguing that deep events are poorly understood and deserve further study

(C) defending a revolutionary theory about the causes of earthquakes and methods of predicting them

(D) discussing evidence for the existence of deep events and the conditions that allow them to occurC

(E) comparing the effects of shallow events with those of deep events

这题我觉得DC也挺象答案的,怎么排除

收藏 分享

D说的只是部分事实,概括不够全面

TOP

主题啊,主题一定得是文章涉及最多的内容噢.

你看D,难道全文说了半天就为了讨论一些evidence?显然不是吗.

另外你是不是打错了?C不就是正确答案吗?是不是你怀疑E啊?E也同样是范围太狭窄,概括不了全文.

TOP

感谢!!

TOP

返回列表

站长推荐 关闭


美国top10 MBA VIP申请服务

自2003年开始提供 MBA 申请服务以来,保持着90% 以上的成功率,其中Top10 MBA服务成功率更是高达95%


查看