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Prior to 1965 geologists assumed
that the two giant rock plates meeting at
the San Andreas Fault generate heat
Linethrough friction as they grind past each
(5)other, but in 1965 Henyey found that
temperatures in drill holes near the
fault were not as elevated as had
been expected. Some geologists
wondered whether the absence of
(10)friction-generated heat could be
explained by the kinds of rock com-
posing the fault. Geologists’ pre-1965
assumptions concerning heat gen-
erated in the fault were based on
(15)calculations about common varieties of
rocks, such as limestone and granite;
but “weaker” materials, such as clays,
had already been identified in samples
retrieved from the fault zone. Under
(20)normal conditions, rocks composed of
clay produce far less friction than do
other rock types.
In 1992 Byerlee tested whether
these materials would produce friction
(25)10 to 15 kilometers below the Earth’s
surface. Byerlee found that when clay
samples were subjected to the thou-
sands of atmospheres of pressure
they would encounter deep inside the
(30)Earth, they produced as much friction
as was produced by other rock types.
The harder rocks push against each
other, the hotter they become; in other
words, pressure itself, not only the
(35)rocks’ properties, affects frictional
heating. Geologists therefore won-
dered whether the friction between the
plates was being reduced by pockets
of pressurized water within the fault that
push the plates away from each other.
Q6:
The passage mostly agree that Heney’s findings about temperature in the San Andreas Fault made the greatest contribution in that they
A. revealed an error in previous measurements of temperature in the San Andreas Fault zone
B. indicated the types of clay present in the rocks that form the San Andreas Fault
C. established the superiority of a particular technique for evaluating data concerning friction in the San Andreas Fault
D. suggested that geologists had inaccurately assumed that giant rock plates that meet at the San Andreas Fault generate heat through friction
E. confirmed geologists’ assumptions about the amount of friction generated by common varieties of rocks, such as limestone and granite
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发表于 2010-7-21 20:19:53
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