The Húsavík-Flatey Fault is a roughly 100-kilometre right-lateral transform running from onshore Húsavík northwest across Skjálfandi Bay into the Tjörnes Fracture Zone. It is one of two main strands that link the Northern Volcanic Zone to the offshore Kolbeinsey Ridge as the Mid-Atlantic plate boundary steps to the west.
It accommodates part of the roughly 2 centimetres per year of relative plate motion, and unusually for Iceland it passes directly beneath the fishing town of Húsavík. Geodetic studies show the fault is largely locked near the coast, quietly building strain that could be released in a single larger event.
The Tjörnes zone produced destructive earthquakes in 1755 and 1872, the latter a pair of magnitude ~6.5 shocks that damaged Húsavík and Flatey island. Because the fault runs through inhabited terrain, it is closely monitored as one of northern Iceland's principal seismic hazards.