I'll be the Devil's Advocate here.
Both moves have a power of 100, but Bonemerang has an Accuracy of 90, which is not horrible.
Here is something Bonemerang can do that Earthquake can't: Break through Subs and cause damage and break through Focus Sash. It's the same reason i put Dual Chop on my Haxorus instead of Dragon Claw: Same Power with added effect.
I would use Bonemerang.