The Marlborough Fault System is a set of four large dextral strike-slip faults and other related structures in the northern part of South Island,

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 ...

, which transfer displacement between the mainly

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plate Plate may refer to: Cooking * Plate (dishware), a broad, mainly flat vessel commonly used to serve food * Plates, tableware, dishes or dishware used for setting a table, serving food and dining * Plate, the content of such a plate (for example: ...

boundary of the

Alpine fault The Alpine Fault is a geological fault that runs almost the entire length of New Zealand's South Island (c. 480 km) and forms the boundary between the Pacific Plate and the Indo-Australian Plate. The Southern Alps have been uplifted on the f ...

and the mainly destructive boundary of the

Kermadec Trench The Kermadec Trench is a linear ocean trench in the south Pacific Ocean. It stretches about from the Louisville Seamount Chain in the north (26°S) to the Hikurangi Plateau in the south (37°S), north-east of New Zealand's North Island. Toget ...

, and together form the boundary between the

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and Pacific Plates.

Geometry

The Marlborough Fault System consists of four main dominantly strike-slip fault strands, which together carry almost all of the displacement associated with the plate boundary. Other smaller faults form as splays of these main faults or accommodate deformation of the crust between them, such as the Newton and Hura Faults at the western end of the Hope Fault and the Jordan Thrust that formed the Seaward Kaikoura Range. The dextral strike-slip across this zone has also involved clockwise rotation of the intervening fault blocks of about 20° since the early

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58

Development

The Marlborough Fault System formed at about 5 Ma, during the early

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58

Faults

There are four main fault strands, although many other smaller faults, of either strike-slip or thrust type are known.

Main Faults

Hope Fault

The Hope Fault forms the southernmost part of the Marlborough Fault System. The estimated slip-rate during the

Holocene The Holocene ( ) is the current geological epoch. It began approximately 11,650 cal years Before Present (), after the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene togeth ...

is 20–25 mm/yr, just over half of the plate boundary displacement. At its northeastern end it links into the Jordan Thrust and most of the displacement is transferred onto that structure. It takes its name from the Hope River, which runs along one of the central fault segments. The Kekerengu Fault and Jordan Thrust are closely associated with the Hope Fault.

Clarence Fault

The Clarence Fault runs from close to the Alpine Fault to about 10 km west of

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, where it appears to terminate abruptly. A Holocene slip-rate of 3.5–5.0 mm/yr is estimated for this fault. At the surface the displacement appears to be nearly pure horizontal, but continuous uplift of the neighbouring Inner Kaikoura Range over the same period, suggests that some of the dip-slip component thought to be present at depth on the fault zone is transferred onto thrust or reverse faults under the range. An extra 10° of clockwise rotation has been recognised within the block that lies northeast of the tip of the Clarence fault. It takes its name from the

Waiau Toa / Clarence River The Clarence River (; officially Waiau Toa / Clarence River) is a major river which flows through the Kaikōura Ranges in the northeast of New Zealand's South Island. At roughly long, it is the longest river in Canterbury and the eighth longest ...

, which follows the fault trace in the northeastern section of the fault.

Awatere Fault

It is formed of two main segments; the Molesworth section to the southwest and the Eastern section to the northeast. The estimated recent slip-rate for the Molesworth section is 4.4 mm/yr. It takes its name from the

Awatere River The Awatere River is a large river flowing through Marlborough, New Zealand. Flowing along the trace of the active Awatere Fault, it runs northeast through a straight valley to the west of the Inland Kaikoura mountains. This valley is paralle ...

whose valley follows the fault trace along some of its length.

Wairau Fault

The Wairau Fault is sometimes regarded as a direct continuation of the Alpine Fault and may be referred to as the Alpine-Wairau Fault. It takes its name from the

Wairau River The Wairau River is one of the longest rivers in New Zealand's South Island. It flows for from the Spenser Mountains (a northern range of the Southern Alps), firstly in a northwards direction and then northeast down a long, straight valley in ...

, which follows the fault trace for most of its length. It has an estimated slip-rate of 3–5 mm/yr.

Smaller Faults

Kekerengu Fault

It is closely associated with the

Hope Fault The Hope Fault is an active dextral (right lateral) strike-slip fault in the northeastern part of South Island, New Zealand. It forms part of the Marlborough Fault System, which accommodates the transfer of displacement along the oblique conver ...

and Jordan Thrust at its south-easternmost edge and likely joins with the Clarence Fault to form the

Wairarapa Fault The Wairarapa Fault is an active seismic fault in the southern part of the North Island of New Zealand. It is a dextral (right lateral) strike-slip fault with a component of uplift to the northwest as expressed by the Rimutaka Range. It forms pa ...

offshore in

Cook Strait Cook Strait ( mi, Te Moana-o-Raukawa) separates the North and South Islands of New Zealand. The strait connects the Tasman Sea on the northwest with the South Pacific Ocean on the southeast. It is wide at its narrowest point,McLintock, A ...

. Before joining with the Clarence Fault, The offshore segment of the Kekerengu Fault is known as the Needles Fault. Both the Kekerengu Fault and the Needles Fault ruptured in the 7.8 ()

2016 Kaikoura earthquake Sixteen or 16 may refer to: *16 (number), the natural number following 15 and preceding 17 *one of the years 16 BC, AD 16, 1916, 2016 Films * ''Pathinaaru'' or ''Sixteen'', a 2010 Tamil film * ''Sixteen'' (1943 film), a 1943 Argentine film d ...

Elliott Fault

The Elliott Fault branches from the central portion of the Clarence Fault and then rejoins it.

Kelly Fault

The Kelly Fault forms a major fork of the Hope Fault from just west of Harper Pass; it forks again to the west into the Newton and Hura faults just before connecting to the Alpine Fault.

Jordan Thrust

The Jordan Thrust is a

reverse fault In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectoni ...

that connects the southern end of the Kekerengu Fault to the Seaward Segment of the Hope Fault.

Seismicity

All parts of the Marlborough Fault System are currently seismically active. Historical earthquakes (since European settlement) have occurred on both the Hope and Awatere Faults and on the smaller Poulter Fault. Studies of the geomorphology and the use of trenching across fault strands, has identified many earthquakes that occurred during the Holocene on many parts of the fault system. The Hope Fault, which has the fastest slip rate is characterised by the shortest recurrence interval.

References

{{Seismic faults of New Zealand Seismic faults of New Zealand Geographic areas of seismological interest