急求：GWD地震P波S波那篇。明天就考了，一直没找到，谢谢！

im_water

RT

马上上战场了，这个月的JJ里都说是“GWD地震P波S波”那篇，没给具体的，汗啊～

翻了很久，没翻到。时间有限，麻烦知道原文的贴一下。

万分感谢！

coral3

In most earthquakes the Earth’s

crust cracks like porcelain, Stress

builds up until a fracture forms at a

line depth of a few kilometers and the crust

(5) slips to relieve the stress. Some

   earthquakes, however, take place hun-

   dreds of kilometers down in the Earth’s

   mantle, where high pressure makes

   rock so ductile that it flows instead of

(10) 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.

(15) when the seismologist Kiyoo Wadati

convincingly demonstrated their exis-

tence. Instead of comparing the arrival

times of seismic waves at different

locations, as earlier researchers had

(20) done, Wadati relied on a time differ-

ence between the arrival of primary(P)

waves and the slower secondary(S)

waves. Because P and S waves

travel at different but fairly constant

(25) speeds, the interval between their

arrivals increases in proportion to the

distance from the earthquake focus,

or initial rupture point.

 For most earthquakes, wadati dis-

(30) covered, the interval was quite short

near the epicenter; the point on the sur-

face where shaking is strongest. For

a few events, however, the delay was

long even at the epicenter. Wadati saw

(35) a similar pattern when he analyzed data

on the intensity of shaking. Most earth-

quakes had a small area of intense

shaking, which weakened rapidly with

increasing distance from the epicenter.

(40) 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 a focus several

hundred kilometers down.

   The question remained: how can

(50) such quakes occur, given that mantle

rock at a depth of more than 50 kilo-

meters is too ductile to store enough

stress to fracture? Wadati’s work sug-

gested that deep events occur in areas

(55) (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

(60) hence is less ductile and much more

liable to fracture.

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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.

Answer:

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31.

information presented in the passage sug-

gests 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.

Answer:

-------------------------------------------------------------------------------------------------------

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.

Answer:

-------------------------------------------------------------------------------------------------------

33.

The passage suggests that which of the

following must take place in order for any

earthquake to occur?

1.Stress must build up.

2.Cool rock must descend

into the mantle.

3.A fracture must occur

(A)  1 only

(B)  2 only

(C)  3 only

(D)  1 and 3 only

(E)   1, 2, and 3

im_water

多谢多谢！

大家～一切顺利啊！