 The topmost, brittle part of the Earth's crust, and the cool slabs of the tectonic plates that are descending down into the hot mantle, are the only parts of our planet that can store elastic energy and release it in fault ruptures.Rocks hotter than about flow in response to stress; they do not rupture in earthquakes.The maximum observed lengths of ruptures and mapped faults (which may break in a single rupture) are approximately .