Active Margin

An active margin is a continental margin that coincides with a tectonic plate boundary, so it is seismically and volcanically alive. Most are convergent, where oceanic lithosphere subducts beneath the continent and builds a trench, an accretionary prism, and a volcanic arc, as along the Pacific rim. The shelf is narrow, the slope steep, and the continental rise often absent because a trench traps downslope sediment. Earthquakes are frequent and deep, following the dipping seismic zone. Contrast this with a passive margin, which sits inside a plate far from any boundary and accumulates a thick, quiet sediment wedge.