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
Tonga Trench midway between two large oceanic plateaux north and south of the Tonga Trench respectively: Manihiki to the north and Hikurangi to the south. These plateaux once formed part of the Ontong Java-Manihiki-Hikurangi large igneous province (LIP). Spreading between the plateaux ceased when Hikurangi collided with the Chatham Rise east of New Zealand at 86 Ma. The western end of the Osbourn Trough is bounded by the Tonga Trench and its eastern by the Wishbone–East Manihiki Scarp. In between the Osbourn Trough is divided into three segments separated by dextral offsets. Near the Tonga Trench the bathymetry of these structures is