This has a lot of assumptions, for there is no official size. Feat can be seen here.
The one who requested this calc says the moon's probably around mountain-sized. In lack of better options, I'll use that.
According to this, the size of a small mountain is 7.586e+14 cm^3.
Density of the moon is 3.344 g/cm^3.
7.586e+14*3.344 = 2 536 758 400 000 000 grams, or 2 536 758 400 000 kilograms.
The moon is a sphere.
A moon that big will have a diametre of around metres. What a tiny moon.
Diametre of moon: 212 px or 1131.54 metres
Distance apart the two halves of the moon: 35 px, 187 metres
The centre of mass of each individual half is 3R/8 from the centre of the sphere.
U = GMm/r
M = m = mass of half of the moon = 1 268 379 200 000 kg
G = Gravitational constant = 6.674×10^(−11) m^3⋅kg^(−1)⋅s^(−2)
r = moon radius = 565.77 m
Moon Split Width = 187 m
GPE of the unsplit moon: 6.674×10^(−11)*1268379200000*1268379200000/[2*(3/8)*565.77] = 2 53 036 543 607.9651 Joules
GPE of the split moon: 6.674×10^(−11)*1268379200000*1268379200000/[2*(3/8)*56.5+187] = 413 913 235.7172295 Joules
Subtracting the higher value with the lower value, I get 252 622 630 372.2478 Joules, or City Block level+.
Kinetic Energy[]
Executor N0 said K.E. might get a higher result.
It took 2 seconds or so for the moon to split apart. Since it broke in two let's find the KE of one piece.
First we half the distance between the two parts.
187/2 = 93.5
Then we find speed.
93.5/2 = 46.25 m/s
1268379200000*46.25^2*0.5 = 1 356 571 191 250 000 Joules
Multiply by two since that's only one piece.
2 713 142 382 500 000 Joules, Large Town level+