The Kerepehi Fault (also known as the Kerepēhi Fault) is a NeS-to NWeSE-striking normal fault system in the

North Island The North Island, also officially named Te Ika-a-Māui, is one of the two main islands of New Zealand, separated from the larger but much less populous South Island by the Cook Strait. The island's area is , making it the world's 14th-largest ...

New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island count ...

aligned with the Hauraki rift valley that produced the

Firth of Thames The Firth of Thames ( mi, Tikapa Moana-o-Hauraki) is a large bay located in the north of the North Island of New Zealand. It is the firth of the rivers Waihou and Piako, the former of which was formerly named the Thames River, and the town o ...

and the

Hauraki Plains The Hauraki Plains are a geographical feature and non-administrative area (though Hauraki Plains County Council existed from 1920 to 1989 and a statistical Area Unit remains) located in the northern North Island of New Zealand, at the lower ( ...

. The Kerepehi Fault has a maximum potential of generating earthquakes with magnitudes of or above.

Geology

The Kerepehi Fault in the southern portion of the

Hauraki Rift The Hauraki Rift is an active NeS-to NWeSE-striking rift valley system in the North Island of New Zealand that has produced the Firth of Thames and the Hauraki Plains. It is approximately wide and long. Geology The rift valley in the north app ...

is much more complex than previously thought and as a result has the potential for large earthquakes, although single fault segment events should be less than 7 in magnitude. Previously it was thought to contain 5 fault segments with events separated by many thousands of years of moderate magnitude but the mean event separation anywhere in the fault zone is now known to be only about 1000 years in what is a belt of many faults and at least 6 complex segments on land. Three segments have been identified under the sea. The fault system extends therefore from

Waiheke Island Waiheke Island (; Māori: ) is the second-largest island (after Great Barrier Island) in the Hauraki Gulf of New Zealand. Its ferry terminal in Matiatia Bay at the western end is from the central-city terminal in Auckland. It is the most pop ...

to south of

Te Poi Te Poi is a small village in rural Waikato, New Zealand, established in 1912 at the base of the Kaimai Range. Te Poi is part of a thriving farming area, particularly for dairying, thoroughbred horse breeding and cropping. The village is servic ...

and is the intra-rift fault structure for the now geologically fairly inactive by New Zealand standards,

. Work using geolocation on the Hauraki Rift which is a North - South trending, long and wide on-shore/off-shore continental rift reveals a widening rate of /year although some of the raw data suggests that at the

end it might be up to /year. The recently identified but yet to be fully characterised 25 km long Te Puninga fault is presumably a parallel intra-rift fault much closer to the western borders of the

Hazards

Earthquake Hazards

Recent historic ruptures have involved up to of vertical displacement, which suggests associated contemporary earthquake risk that could be of seismic intensity VII on the

Modified Mercalli intensity scale The Modified Mercalli intensity scale (MM, MMI, or MCS), developed from Giuseppe Mercalli's Mercalli intensity scale of 1902, is a seismic intensity scale used for measuring the intensity of shaking produced by an earthquake. It measures the eff ...

at the nearby major population centres, being

Auckland Auckland (pronounced ) ( mi, Tāmaki Makaurau) is a large metropolitan city in the North Island of New Zealand. The List of New Zealand urban areas by population, most populous urban area in the country and the List of cities in Oceania by po ...

Hamilton Hamilton may refer to: People * Hamilton (name), a common British surname and occasional given name, usually of Scottish origin, including a list of persons with the surname ** The Duke of Hamilton, the premier peer of Scotland ** Lord Hamilt ...

Tauranga Tauranga () is a coastal city in the Bay of Plenty region and the fifth most populous city of New Zealand, with an urban population of , or roughly 3% of the national population. It was settled by Māori late in the 13th century, colonised by ...

and

Thames The River Thames ( ), known alternatively in parts as the River Isis, is a river that flows through southern England including London. At , it is the longest river entirely in England and the second-longest in the United Kingdom, after the R ...

. Forty percent of New Zealand's population live, and 40% of GDP generation occurs within of the fault. A major magnitude 8 to 10 event resulting from up to 3 segment rupture would be devastating to

infrastructure.

Tsunami Hazards

At least a third of the fault structure is likely to be underwater and thus will offer a tsunami hazard to the low-lying areas of the Hauraki Plains and shore areas of the

and

Hauraki Gulf The Hauraki Gulf / Tīkapa Moana is a coastal feature of the North Island of New Zealand. It has an area of 4000 km2,

Historical Earthquakes

In the past, the Kerepehi Fault has experienced significant earthquakes that might have occurred before the advent of written records. However, the following list consists of recently occurred quakes along the fault(s), as far back as the year 1900. *1926 Magnitude 4.6 *1927 Magnitude 5.5 *1972 Magnitude 4.9 *2023 Magnitude 5.1 *2023 Magnitude 4.8

References

{{Seismic faults of New Zealand Seismic faults of New Zealand Thames-Coromandel District Firth of Thames Hauraki District