Answer
6.31 times more intense
Work Step by Step
Given the magnitude equation $M = \log \frac{I}{S}$
with $S = 10^{-4}$
The question asks for how much more intense the 2011 Japan earthquake (M= 9.1) was compared to the San Francisco Earthquake (M = 8.3) in 1906.
S is a constant that is already factored into the Magnitudes, so the $10^{-4}$ isn't necessary
$(9.1 - 8.3) = \log I$
$10^{0.8} = {I}$
$I = 6.31$ times more intense
