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What is the magnitude of the aftershock

  1. Jun 28, 2015 #1
    1. The problem statement, all variables and given/known data

    An earthquake with a magnitude of 5.4 is 39 times as intense as an aftershock that occurs 5 hours later. What is the magnitude of the aftershock.
    2. Relevant equations

    3. The attempt at a solution
    I know that I what to find the magnitude
    I am stuck because I do not know what # do I replace "/i_0' with..please help!?
  2. jcsd
  3. Jun 28, 2015 #2


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    Homework Helper

    You don't need it, the i_0 is irrelevant.
    Look at it this way: m1 = 5.4 = log(39x/i_0) = log(39x) - log(i_0).
    and m = log(x/i_0) = log(x) - log(i_0).
    You can cancel out the i_0, since it won't help you.

    *edit* Even more simply, let x= i/i_0, then there is even less to worry about. Just remember the product rule for logarithms.
    Last edited: Jun 28, 2015
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