The primary coverages Pete Carroll has run with the Seattle Seahawks have been a single-high safety Cover 1 and Cover 3. There’s a perception of Carroll’s defense being simple. Though the overall rules of his defense are basic and consistent, Carroll is still an innovator. If a coach is too schematically simple in the NFL you die; just look at how Chip Kelly was dragged down by his overly predictable run game.
Carroll, then, uses a variety of coverages that have their basis in Cover 1 and Cover 3. Coming into the Detroit Lions game, the Seahawks ran Middle of the Field Closed coverages 77% of the time.