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active margin (seismic margin) The margin of a continent that is also a plate margin. The alternative term, ‘Pacific-type margin’, indicates the range of features (e.g. earthquakes, andesitic (see ANDESITE) volcanic chains, offshore oceanic trenches, and young fold mountains) which may be associated with active margins. Some authors distinguish an ‘Andino-type margin’, involving an oceanic and a continental plate, from a ‘Japan-type margin’, involving an oceanic plate and an island arc. The term ‘Mediterranean-type margin’ is also in use, although to a lesser extent, to signify the coincidence of continental edges and plate margins in a collision zone.