The North Island Fault System (NIFS) (also known as North Island Dextral Fault Belt or North Island Shear Belt) is a set of southwest–northeast trending seismically-active faults in the North Island of New Zealand that carry much of the dextral (right lateral) strike-slip component of the oblique convergence of the Pacific Plate with the Australian Plate. However despite at least of uplift of the axial ranges in the middle regions of the fault system during the last 10 million years most of the shortening on this part of the Hikurangi Margin is accommodated by subduction.
The faults include the Wairarapa Fault and Wellington Fault to the southwest, the Ruahine and Mohaka Faults in the central section and the Waimana, Waiotahi, Whakatane and Waiohau Faults to the northeast. Most of the fault system consists of dextral strike-slip faults, although towards its northeastern end the trend swings to more S-N trend and the faults become mainly oblique normal in sense as the zone intersects with the Taupō Rift. This fault zone accommodates up to of strike-slip displacement.
Faults
The North Island Fault System consists of eight main fault strands and many smaller related faults that are also currently active.
Mohaka Fault
The more southeasterly branch of the Wellington Fault is known as the Mohaka fault. The fault splays to the north, onto the Waimana Fault, which itself has branches of the Waiotahi and Waioeka Faults. The Waimana Fault is long with potential for a shock at its recurrence interval of 2850 years and slip rate of . The main segment of the Mohaka Fault eventually passes into the Whakatane Fault which has an off shore extension. The Whakatane Fault has multisegment capacity for a size earthquake at a recurrence interval of 3000 years and slip rate of . To the east of the Mohaka Fault is the Patoka Fault which commences in the Tutaekuri River valley within of a Mohaka Fault splay. Where the Potaka Fault intercepts the Esk Forest its most eastern active splay becomes the Rukumoana Fault. The Potaka Fault terminates just south of the peak Tauwhare Papauma on State Highway 5. The Rukumoana Fault has an active northern splay called the Rangiora Fault and both terminate in the region of Hawke's Bay north of Lake Tutira. Where the Rangiora Fault terminates the Waiotahi Fault to its north by about becomes the most eastern active fault in the system.
There has been a transition from episodic dip-slip-dominated displacement during the late Miocene–Pliocene to oblique-slip and strike-slip-dominated offset more recently. Prior to the late Miocene, before about 11 million years ago, at least of western vertical displacement occurred on the Mohaka Fault, and more recently, in the last 2.3 million years the maximum vertical displacement has been at least a further found about south of Hawkston. It is noted that at Hawkston itself there has been no vertical displacement although both the southern end and northern end of the fault there has been vertical displacement during this period. The souther displacement of about produced the Wakarara Range. The Mohaka Fault has had about of strike-slip displacement in the last 2 million years.