An 8.6 magnitude earthquake occurred 62 miles off the coast of Sumatra on April 11th, 2012. Along with being severe by any measure, in one way it was the largest earthquake in observed human history; it originated within the plate rather than at a plate boundary.
In 1981, scientists discovered one of the thinnest portions of the Earth's crust a 1-mile (1.6 kilometers) thick, earthquake-prone spot under the Atlantic