The Dien Bien basin in the Northwest of Vietnam is the largest one of the pull-apart basins related to the Dien Bien - Lai Chau fault zone. This basin, orientated from the north to the south, is 21km long, 6-8km wide and rhomboidal in shape. The process of forming this basin is related closely to the activities of the Dien Bien - Lai Chau fault zone in Neotectonic time. On analyzing information concerning the kinematics of the Dien Bien - Lai Chau fault zone, the geological structure and the sediments of the basin, we suppose that the Dien Bien basin is a splay pull-apart one related to the movement of the Dien Bien - Lai Chau fault zone in Pliocen-Quaternary time. The determination of the mechanism of forming the Dien Bien basin is important to specify Neotectonic activities of the Dien Bien - Lai Chau fault zone
