Automatic doomsday machine on the moon

[gmathiowitz]

Many years ago I read a very short sci-fi story about an ancient alien doomsday machine buried under the surface of the moon and unintentionally awakened by a random tremor or a meteorite hitting the surface. The automatic doomsday machine was a long-forgotten relic of a bygone space war between two unknown alien races. It had been waiting patiently for untold millennia and was in an advanced state of decay. However, the tremor set a chain of events and internal states in motion, each more precarious than the other, which nevertheless resulted in the launch of a salvo of doomsday missiles that annihilated present day Earth (which might have been an outpost of the other alien race in the remote past).

Anybody out there knows anything at all about the name of the story and/or the author? Does it ring a bell to anyone?