什么是 Active margin, oceanic trench, forearc, back-arc basin？

An active margin is a convergent plate boundary at which oceanic lithosphere sinks beneath another plate, either beneath a continent or beneath another oceanic plate. An oceanic trench is the long, narrow, V-shaped depression of the sea floor along which the sinking plate bends down beneath the other. The forearc is the part of the overriding plate between the trench and the line of volcanoes. A back-arc basin is a basin behind the volcanoes, on the side away from the trench, where the overriding plate is stretched and new oceanic crust may form.