Final answer:
The subject of this question is Geography. The student is asking about the zone where plates sink into the upper mantle, causing earthquakes. This zone is called a subduction zone.
Step-by-step explanation:
The subject of this question is Geography. The plates that make up the lithosphere can sink into the upper mantle, causing earthquakes along their upper boundary. This zone is called a subduction zone. In a subduction zone, one tectonic plate is forced beneath another plate, usually where an oceanic plate is being subducted beneath a continental plate. This process can result in the formation of trenches and volcanic activity.