thumb|300px|Red line indicates the bathymetric low of the Ryukyu Trench
The , also called Nansei-Shotō Trench, is a 1398 km (868 mi) long oceanic trench located along the southeastern edge of Japan's Ryukyu Islands in the Philippine Sea in the Pacific Ocean, between northeastern Taiwan and southern Japan. The trench has a maximum depth of 7460 m (24,476 ft). at a rate of approximately 52 mm/yr. In conjunction with the adjacent Nankai Trough to the northeast, subduction of the Philippine plate has produced 34 volcanoes.
The largest earthquake to have been recorded along the Ryukyu Trench, the 1968 Hyūga-nada earthquake,
was magnitude 7.5 and occurred along the northernmost part of the trench This earthquake also produced a tsunami.
Ryukyu Trench and Ryukyu Arc structure near Taiwan
thumb|Undersea geographic features of the western Pacific
An east-west planar seismic zone associated with the Ryukyu Trench occurs off the east coast of Taiwan. This seismic zone is continuous laterally for 50 km and to 150 km depth. The hypocenters of earthquakes at this location outline a Wadati–Benioff zone indicating that the Philippine Sea plate is subducting at an angle of about 45° beneath the Eurasian plate in this area; the dip of the slab changes dramatically from one end of the trench to the other as noted in the next section. Such depth and dip inferences of this area are consistent with the positions of the overlying Tatun and Chilung volcano groups of Taiwan. The transect perpendicular to the length of the trench images many distinct velocity layers. The sedimentary wedge created by subduction has four distinct layers with P wave velocities of 1.8 km/s, 2.8-2.9 km/s, 3.5 km/s, and 4.5–5 km/s. In the area of this transect, the wedge reaches a thickness of 9 km at 50 km from the trench. Beneath the wedge are several seismic layers within the oceanic crust.
Separate ocean bottom seismography and multi-channel seismic studies provide insight into the structure of the northern end of the Ryukyu trench region. Features of note include a thick (7–12 km) low velocity (4–5 km/s) zone on the landward side of the trench, the existence of subducting paleo-arc crust near the top of the trench in contrast to simple oceanic crust located at the middle of the trench, and a zone in which the Philippine Plate subducts beneath low P wave velocity material (Vp = 5 km/s) that coincides with the location of the 7.5 1968 Hyūga-nada earthquake.