The given blank can be filled with the Deep-oceanic trench.
Any long, narrow steep-edged depression in the bottom of the ocean in which the maximum oceanic depths occurs is known as a deep-oceanic or deep-sea trench. They are about 7000 to 11000 meters in depth.
They generally originate in the regions where one tectonic plate subducts over another. Mariana Trench is the deepest known depression of this type and is situated in the east of the Mariana Islands in the western North Pacific Ocean.