The Matata Fault zone is a seismically active area in the Bay of Plenty Region of the central

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 ...

with potential to rupture as part of an event.

Geology

The Matata Fault zone is the northwestern wall fault of the Whakatāne Graben and extends from the coast near

Matatā Matatā is a town in the Bay of Plenty in the North Island of New Zealand, to the north-west of Whakatāne. Much of the town was relocated between the years 2006 and 2021 due to increased natural threats arising from climate change. As an ...

to where the boundary of the modern

Taupō Rift The Taupō Rift is the seismically active rift valley containing the Taupō Volcanic Zone, central North Island of New Zealand. Geology The Taupō Rift (Taupo Rift) is a intra-arc continental rift resulting from an oblique convergence in the Hik ...

changes direction to a mainly SSE-dipping fault trace of the

Manawahe Fault The Manawahe Fault line is a seismically active area in the Bay of Plenty Region of the central North Island of New Zealand with the potential to be involved with other faults in an event. Geology North of Lake Rotoma, volcanic ignimbrite shee ...

. At this southern end of the fault there is an area of Manawahe

dacite Dacite () is a volcanic rock formed by rapid solidification of lava that is high in silica and low in alkali metal oxides. It has a fine-grained (aphanitic) to porphyritic texture and is intermediate in composition between andesite and rhyolite. ...

that has been dated to 425,000 ± 27,000 years ago. There has been considerable uplift of Castlecliffian (mid

Quaternary The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS). It follows the Neogene Period and spans from 2.58 million years ...

) marine sediments at a rate of /year to more than above sea level. An earthquake swam that commenced in 2005 at the northern end of the Matata Fault zone progressed off shore and lasted until 2009. At the coast there was an area of transition of a few miles with lower current seismic activity to defined off shore faults. These earthquakes were also associated with about of area that has risen by up to since the 1950s. The increase of height over this area is not thought to be consistent with a pure tectonic origin but would be consistent with inflation from the accumulation of

magma Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma is found beneath the surface of the Earth, and evidence of magmatism has also been discovered on other terrestrial planets and some natural sa ...

at a depth of about . This magma body was later interpreted as a newly stalled

sill Sill may refer to: * Sill (dock), a weir at the low water mark retaining water within a dock * Sill (geology), a subhorizontal sheet intrusion of molten or solidified magma * Sill (geostatistics) * Sill (river), a river in Austria * Sill plate, a ...

under the northern Matata Fault.

Risks

During the period 2005 to 2009 an earthquake swarm occurred near Matatā with many low magnitude earthquakes and one of . A potentially whole fault rupture could be up to if the fault ruptured at the same time as the shorter Manawahe Fault which is a continuation. Volcanic eruption risk is not negligible given the past eruption of Manawahe Massif

andesite Andesite () is a volcanic rock of intermediate composition. In a general sense, it is the intermediate type between silica-poor basalt and silica-rich rhyolite. It is fine-grained (aphanitic) to porphyritic in texture, and is composed predomi ...

and the coupling of the Manawahe Fault with other eruptions.

References

{{Seismic faults of New Zealand Seismic faults of New Zealand Taupō Volcanic Zone Okataina Volcanic Centre Geography of the Bay of Plenty Region Whakatane Graben