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    #1

    seismic-reflection method would be likely to yield an inaccurate physical profile ...

    Hi, would you please help me to understand the correct answer of the following question, related to the below reading. Thanks a lot.
    Reading
    Because of its accuracy in outlining the Earth‟s subsurface, the seismic-reflection method remains the most important tool in the search for
    petroleum reserves. In field practice, a subsurface is mapped by arranging a series of wave-train sources, such as small dynamite explosions, in a grid pattern. As each source is activated, it generates a wave train that moves downward at a speed determined uniquely by the rock‟s elastic characteristics. As rock interfaces are crossed, the elastic characteristics encountered generally change abruptly, which causes part of the energy to be reflected back to the surface, where it is recorded by seismic instruments. The seismic records must be processed to correct for positional differences between the source and the receiver, for unrelated wave trains, and for multiple reflections from the rock interfaces. Then the data acquired at each of the specific source locations are combined to generate a physical profile of the subsurface, which can eventually be used to select targets for drilling.


    19.It can be inferred from the passage that the seismic-reflection method would be likely to yield an inaccurate physical profile of the subsurface in which of the following circumstances?
    (A) If the speed at which the wave train moved downward changed
    (B) If the receiver were not positioned directly at the wave-train source
    (C) If the rock on one side of a rock interface had similar elastic characteristics to

    those of the rock on the other side
    (D) If the seismic records obtained for the different sources in a grid were highly similar to each other

    (E) If there were no petroleum deposits beneath the area defined by the grid of wave-train sources

    Answer: The correct answer is C, but I cannot understand why. Would you please help. Thanks.

  1. Piscean's Avatar
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    #2

    Re: seismic-reflection method would be likely to yield an inaccurate physical profile

    Quote Originally Posted by tesoke View Post
    As rock interfaces are crossed, the elastic characteristics encountered generally change abruptly, which causes part of the energy to be reflected back to the surface, where it is recorded by seismic instruments.

    (C) If the rock on one side of a rock interface had sim
    ilar elastic characteristics to those of the rock on the other side, theer would be nothing to cause part of the energy to be reflected back to the surface.

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    #3

    Re: seismic-reflection method would be likely to yield an inaccurate physical profile

    Quote Originally Posted by Piscean View Post
    [/FONT][/COLOR][/SIZE]
    (C) If the
    rock on one side of a rock interface had sim
    ilar elastic characteristics to those of the rock on the other side, theer would be nothing to cause part of the energy to be reflected back to the surface.
    Thank you, but sorry, I cannot understand the meaning of the red part. So, it leads me to not understand why C is correct. Would you please explain its meaning? Thanks a lot.

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