Intracontinental and marine rift basins such as the Gulf of Suez, East African Rift, Rio Grande rift system and the North Sea often contain a series of half-graben sub-basins, with the polarity of the dominant fault system changing along the axis of the rift. Often the extensional fault systems are segmented in these rifts. Rift border faults with lengths over 10 kilometres (6.2 mi) are separated by relay ramp structures.