Half-graben

A half-graben is a geological structure in which a block of crust has dropped down along a fault on only one side, in contrast to a full graben, which is bounded by roughly parallel faults on both sides. It forms where the crust is being pulled apart by extensional forces, so that one edge of the down dropped block is controlled by a sloping fault while the opposite edge has no matching fault and instead tilts gently upward. This asymmetry gives a half-graben a lopsided profile rather than the more symmetrical trough of a true graben. Half-grabens are common features in rift zones around the world and often fill with sediment and water as they continue to subside over geological time.