The Okinawa Trough (沖縄トラフ, Okinawa Torafu) (also called Chinese: 中琉界沟, literally "China-Ryukyu Border Trough") is a seabed feature of the East China Sea. It is an active, initial back-arc rifting basin which has formed behind the Ryukyu arc-trench system in the West Pacific. It developed where the Philippine Sea Plate is subducting under the Eurasia Plate.
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👉 Okinawa Trough in the context of First island chain
The first island chain is the first string of major Pacific archipelagos out from the East Asian continental mainland coast. It is principally composed of the Kuril Islands, the Japanese archipelago, the Ryukyu Islands, Taiwan (Formosa), the northern Philippines, and Borneo, hence extending all the way from the Kamchatka Peninsula in the northeast to the Malay Peninsula in the southwest. The first island chain forms one of three island chain doctrines within the island chain strategy in the U.S. foreign policy. It is considered a strategic military barrier to accessing the wider Pacific Ocean given the relative shallowness of waters to the west of the first island chain, which has important implications for submarine detection.
Much of the first island chain is roughly situated in waters claimed by the People's Republic of China (PRC). These include the South China Sea, within the disputed nine-dash line, as well as the East China Sea west of the Okinawa Trough.
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Okinawa Trough in the context of Yangtze plate
The Yangtze plate, also called the South China block or the South China subplate, comprises the bulk of southern China. It is separated on the east from the Okinawa plate by a rift that forms the Okinawa Trough which is a back-arc basin, on the south by the Sunda plate and the Philippine Sea plate, and on the north and west by the Eurasian plate. The Longmenshan Fault on the latter border was the site of the 2008 Wenchuan earthquake.
The Yangtze plate was formed by the disaggregation of the Rodinia supercontinent 750 million years ago, in the Neoproterozoic era. South China rifted away from the Gondwana supercontinent in the Silurian. During the formation of the great supercontinent Pangaea, South China was a smaller, separate continent located off the east coast of the supercontinent and drifting northward. In the Triassic, the Yangtze plate collided with the North China plate, thereby connecting with Pangaea, and formed the Sichuan basin. In the Cenozoic, the Yangtze plate was influenced by the collision of the Indian plate and Eurasian plate creating the uplifting of the Longmen Mountains. Its southward motion is accommodated along the Red River fault.