ＧＷＤ－２４－３６，之前没有讨论过

paoma

GWD-24-Q30 ~ 33

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.

Q36：It can be inferred from the passage that if the S waves from an earthquake arrive at a given location long after the P waves, which of the following must be true?

1. The earthquake was a deep event.

2. The earthquake was a shallow event.

3. The earthquake focus was distant.

4. The earthquake focus was nearby.

5. The earthquake had a low peak intensity.

这题答案说是A, 我觉得是C啊, 大家的想法呢？谢谢！

Hamiton

支持选C, 答案绝对错了

Icanw

我的版本的答案居然是D.
我还是支持C.

ggxxtogether

确定是否deep event单单凭p and S waves 的interval 长短是不够的，还有intensity的程度。所以，原文条件只能推出C,因为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.