The North Dogger Fault Zone is located at the northern margin of the UK Southern North Sea Basin, at the edge of the mobile Zechstein Supergroup, and was particularly active during late Triassic and early Jurassic times. It resembles geometrically, and is related tectonically to, the Dowsing Fault Zone which was initiated in late Scythian time along the southwestern edge of the mobile salt. It is proposed that both of these basin-bounding fault systems were initiated in response to the buoyant growth of salt swells in the centre of the Southern North Sea Basin. Passive folding of the Triassic strata over the swells, which accommodated the shape changes caused by halokinesis, led to extension on the fault zones at the edge of the mobile Zechstein salt.