sentences:  The northern boundary of the IBM arc system follows the Nankai Trough northeastward and onto southern Honshū, joining up with a complex system of thrusts that continue offshore eastward to the Japan Trench.The intersection of the IBM, Japan, and Sagami trenches at the Boso Triple Junction is the only trench-trench-trench triple junction on Earth.The IBM arc system is bounded on the east by a very deep trench, which ranges from almost 11 km deep in the Challenger Deep to less than 3 km where the Ogasawara Plateau enters the trench.