首页
登录
职称英语
In most earthquakes the Earth’s crust cracks like porcelain. Stress builds u
In most earthquakes the Earth’s crust cracks like porcelain. Stress builds u
游客
2025-04-05
28
管理
问题
In most earthquakes the Earth’s crust cracks like porcelain. Stress builds up until a fracture forms at the 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 a rupture point.
For most earthquakes, Wadati discovered, the interval was quite short near the epicenter, the point on the surface where shaking is the strongest. For a few events, however, the delay was long enough 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 the deep events, with a 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 flexible 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. [br] The passage is primarily concerned with______.
选项
A、demonstrating why the methods of early seismologists were flawed
B、defending a revolutionary theory about the causes of earthquakes and methods of predicting them
C、discussing the evidence for the existence of deep events and the conditions that allow them to occur
D、comparing the effects of shallow events with those of deep events
答案
C
解析
题目问:文章主要是关于什么的?通过文章内容可知,文章主要是向读者介绍deep events的知识。Wadati通过对P waves与S waves的研究发现deep events的存在。不同类型的地震其PS intervals是不同的,因此有了shallow events与deep events的区别。文章也告诉了读者deep events是如何发生的。据此判断,应选择C。
转载请注明原文地址:https://tihaiku.com/zcyy/4027300.html
相关试题推荐
InmostearthquakestheEarth’scrustcrackslikeporcelain.Stressbuildsu
InmostearthquakestheEarth’scrustcrackslikeporcelain.Stressbuildsu
Thefundisfor______distressamongthefloodvictimsinthesoutherncity.A、rel
Thefactthatthegoldeneagleusuallybuildsitsnestonsomehighcliffs______
Thefundisfor______distressamongthefloodvictimsinthesoutherncity.(20
Hewasinextremestateofdistressanddepressionwhenheknewthathehad_____
Noneofthestudentsintheclasslikesthemistress,whoisusedtobeing______
OneofthelargestearthquakeseverrecordedhitonBoxingDay2004.Theresu
OneofthelargestearthquakeseverrecordedhitonBoxingDay2004.Theresu
Mostearthquakesareinremoteareas;buteverynowandthenaquakemay______vo
随机试题
Myjobwastomakeclassroomobservationsandencourageatrainingprogramt
[originaltext]Moreoftenthannot,I’vebeenaskedbymystudentsthisques
Long-marriedcouplesoftenscheduleaweekly"datenight"—aregulareveningou
项目经理在某项目实施阶段的中期发现,由于未预料到的变更,项目经费要花光了,此时应
未经风景名胜区管理机构审核,在风景名胜区内设置、张贴商业广告的,由风景名胜区管理
“养儿防老”是中国人的传统观念,但随着中国老龄化的加剧,仅仅依靠家庭养老是不够的
常见的战术性投资策略包括()。 Ⅰ.交易型策略Ⅱ.多一空组合策略Ⅲ.事件驱
属五行中“水”的音是A:角音 B:羽音 C:徵音 D:宫音 E:商音
牙膏中胶粘剂的作用是( )。A.防止贮存期间固体与液体成分分离 B.降低表面
应急预案评估每( )一次。A.半年 B.一年 C.两年 D.三年
最新回复
(
0
)