Thanks impart to Newton, we can calculate the gravitational force between large objects (like planets) with a formula.

F = G (m1*m2)/r^2.

Because we are referencing the same masses (the moon and the Earth), M1 and M2, we can assign any value to them (greater than 1). Because G is constant, we can assign any value to it (less than 1). (Checkout the Newton website for why we need values greater or less than 1.) Let’s make it easy and set M1 and M2 each equal to 1, and set G equal to 0.1.

The “lunar apogee” is when the moon is furthest from the Earth, and the “lunar perigee” is when the moon is closest to the earth. Respectively each is 254k miles and 220k miles.

Lunar apogee F: F = 0.1(1*1)/254k^2 = 1.55^-12

Lunar perigee F: F = 0.1(1*1)/220k^2 = 2.06^-12

Difference in apogee/perigee = 2.06/1.55 -1 = 32.9%

With a little math and a degree of faith that an additional +15% moon-gravitational force is relevant, we can conclude that the "Super Moon" helped create the earthquake in Japan.