The region where oceanic plates sink down into the asthenosphere is called a subduction zone.

Here's why:

* Oceanic Plates: These are denser than continental plates.

* Asthenosphere: This is a partially molten layer of the Earth's mantle.

* Subduction: When an oceanic plate collides with a continental plate (or another oceanic plate), the denser oceanic plate bends and slides under the less dense plate. This process is called subduction.

Subduction zones are characterized by:

* Deep ocean trenches: Formed where the oceanic plate bends downward.

* Volcanoes and volcanic arcs: Molten rock (magma) rises from the subducting plate, often erupting to form volcanic chains.

* Earthquakes: The movement of the plates at subduction zones creates intense pressure and friction, leading to earthquakes.

Let me know if you'd like more details about subduction zones or any other geological processes!