Complex sentence: The two major fault zones that are most dangerous are the Sulu Trench in the Sulu Sea and the Cotabato Trench, a region of subduction that crosses the Celebes Sea and the Moro Gulf in Southern Mindanao.
Split into simpler sentences: The two major fault zones that are more dangerous are the Sulu Trench in the Sulu Sea and the Cotabato Trench. The Cotabato Trench is a region of subduction that crosses the Celebes Sea and the Moro Gulf in Southern Mindanao.