请问GWD24—31题的答案定位在哪里？谢谢！

frankleizhang

    

1.       
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.

    

    

 

    

 

    

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

 但我觉得 貌似是定位这段话的：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.

请问31题的答案定位在哪里？谢谢！

andylouis

同问