Central Java city and its surrounding regencies have formed a separate special region (equivalent to a province) since Indonesian independence, administrated separately. Located in the middle of the island of Java, the Central Java province is bordered by West Java and East Java provinces. A small portion of its south region is the Yogyakarta Special Region province, fully enclosed on the landward side by the Central Java province. To the north and the south, the Central Java province faces the Java Sea and the Indian Ocean. Central Java includes offshore islands such as Karimun Jawa Islands in the north, and Nusakambangan in
Sumatra Trench to 350 km. The width at Sumatra trench is controlled by sediment input and accretion rate and history. One distinguishing feature of the Sumatra subduction zone is that it has a relatively 120–140 km accretionary prism and a deep forearc basin (so does the rest of the whole Java subduction zone). However it does vary along the trench. The prism is broad and has a relatively shallow surface slope in the northern part, becomes steep and narrow at the central part, then becomes steep and narrow in the southern area. The inner part of the prism forms a NW-SE arc