The Futsu Fault is an active fault at the southeastern edge of the Unzen Graben. It is a normal fault with the land subsidence on the northen side. Unlike the Fukae Fault running parallel to it, the Fukae Fault has a feature that the fault throws on the coastal side are larger than the ones on the mountain side. Due to this feature, the fault plane thrusts into the sea and makes a cape called Futsusaki.