Oceanic trench the level of the surrounding oceanic floor. The greatest ocean depth measured is in the Challenger Deep of the Mariana Trench, at a depth of below sea level. Oceanic lithosphere moves into trenches at a global rate of about 3 km/yr. There are approximately of convergent plate margins, mostly around the Pacific Ocean—the reason for the reference “Pacific-type” margin—but they are also in the eastern Indian Ocean, with relatively short convergent margin segments in the Atlantic Ocean and in the Mediterranean Sea. Globally, there are over 50 major ocean trenches covering an area of 1.9 million km or about 0.5%
Ryukyu Trench 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