High Quality Content by WIKIPEDIA articles! In geology, subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate, sinking into the Earth`s mantle, as the plates converge. These 3D regions of mantle downwellings are known as "Subduction Zones". A subduction zone is an area on Earth where two tectonic plates move towards one another and one slides under the other. Rates of subduction are typically measured in centimeters per year, with the average rate of convergence being approximately 2 to 8 centimeters per year (about the rate a fingernail grows).