What is Japan Trench?

Location: The Japan Trench is a part of the Pacific Ring of Fire, in the floor of the northern Pacific Ocean off northeast Japan. This is an oceanic trench.It extends from the Kuril Islands to the Bonin Islands and is 9,000 metres (29,500 ft) at its deepest. It is an extension of the Kuril-Kamchatka Trench to the north and the Izu-Ogasawara Trench to its south with a length of 800 km (500 mi). 

Formation of japan trench: 

This trench is created when the oceanic Pacific plate subducts beneath the continental Okhotsk Plate. The subduction process causes bending of the downgoing plate, creating a deep-sea trench. Continuing movement on the subduction zone associated with the Japan Trench is one of the main causes of tsunamis and earthquakes in northern Japan including the 2011 Tōhoku megathrust.

Since 1973 the Japan Trench subduction zone has hosted nine events of magnitude 7 or greater. The largest of these, a M 7.8 earthquake approximately 260 km to the north of the March 11 2011 Tōhoku megathrust epicenter, caused 3 fatalities and almost 700 injuries in December 1994. In June of 1978, a M 7.7 earthquake 35 km to the southwest of the March 11 epicenter caused 22 fatalities and over 400 injuries. Large offshore earthquakes have occurred in the same subduction zone in 1611, 1896 and 1933 that each produced devastating tsunami waves on the Sanriku coast of Pacific NE Japan. That coastline is particularly vulnerable to tsunami waves because it has many deep coastal embayments that amplify tsunami waves and cause great wave inundations. The M 7.6 subduction earthquake of 1896 created tsunami waves as high 38 m and a reported death toll of 27,000. The M 8.6 earthquake of March 2, 1933 produced tsunami waves as high as 29 m on the Sanriku coast and caused more than 3000 fatalities. Unlike the recent magnitude 9.0 earthquake, the 1933 earthquake did not occur as the result of thrust faulting on the subduction-zone plate interface, but rather within the Pacific plate just seaward of the Japan Trench.