Answer
$3.0$
Work Step by Step
Substitute $I_{0}$ with $1000I_{0}$ in the formula for R:
$ R=\displaystyle \log\frac{1000I_{0}}{I_{0}}\qquad$ ... reduce $I_{0}$
$=\log 1000$
$=\log 10^{3}$
... Basic Logarithmic Property $\log_{b}b^{x}=x$...
$R=3$
On the Richter scale, the magnitude is 3.0.
