Ceramic cook top went POP, but there's no crack?
I accidentally heated an empty pan on a rear burner of my ceramic top range. I didn't notice until I heard a loud POP. I removed the pan (without a problem) and have examined the glass carefully. While there are numerous minor scratches on all of the burners (the stove is 15 years old), I don't see any cracks.

Is it possible the glass cracked *underneath* the surface, and if so, is it still safe to use the stovetop?

That could have been the cooking element popping and not the glass. Try it, if it works, use it.