Any idea what causes this to happen?
I'm looking to buy a house, I've replaced roofing before but I've never seen anything like this before? The Shingles on the Garage look like a Earthquake fault shifting? The inside looks fine. Before I put in a bid on the property just looking for help as to what may have been going on here? The roof on the house has some issues I believe from high winds from a storm. The property is in SW Michigan.
That looks like a couple of severely warped pieces of roof sheathing. You'll need to remove those and replace with new plywood or OSB.
It's possible that the existing sheathing panels were installed too tightly together, and when they swelled from the Michigan humidity they buckled and the fasteners failed at those rafters.
Sheathing panels should always have a gap of around 1/8-inch between them to give the panels room to expand when they absorb moisture.
Since I'm not there in person to check the underside of the roof, I can't be 100% sure, but that's what it looks like.
That doesn't look like storm damage, though.
Hope this helps!