Where fasteners are visible, look for proper fastener placement, the proper number of fasteners, and improper installation (overdriven/under-driven/driven at an angle).
Look at the areas where the fasteners tore through. Look for proper fastener placement, and the proper number of fasteners according the designation of the wind zone in which the home is located. Most shingle types in high-wind zones should have 6 nails. Normal wind zones… 4 nails.
Improperly-driven nails or nails with undersized heads will reduce the wind resistance of the shingle roof
If shingles have been fastened with staples (which, properly installed, have nearly the same holding power as nails), you’ll see slots instead of holes. Check to see that the staples were oriented with crowns parallel to the long axis of the shingle. Out of parallel is a defective installation of that fastener. If many are out of parallel, the integrity of the roof was compromised by poor fastener installation.