Answer
$631,000,000I_0$
Work Step by Step
Following the definition of Richter scale ratings, we have:
$ log(\frac{I}{I_0})=8.8$
thus $\frac{I}{I_0}=10^{8.8}$
and $I=10^{8.8}I_0\approx631,000,000I_0$
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