What Killed This Tree?

Bark borer lines on this ash look like some kind of ancient cave art.

We're on the lookout for emerald ash borer in Maine, as the north-eastern frontier of its expanding territory. The previous owners of this property had felled this ash tree and left its logs in segments under the back deck. Chopping it up for firewood this morning, I saw that the bark was loose and flaked off in big chunks. Underneath were these beautiful lines, like wood carvings. The lines don't have the S-shaped features that I'm supposed to look for in Emerald Ash Borer attacks. Instead, there are thicker horizontal lines of various widths, with thin vertical lines emanating from them.