The Hope Fault is an

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dextral (right lateral)

strike-slip 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 tectonic ...

in the northeastern part of

South Island The South Island, also officially named , is the larger of the two major islands of New Zealand in surface area, the other being the smaller but more populous North Island. It is bordered to the north by Cook Strait, to the west by the Tasman ...

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 ...

. It forms part of the

Marlborough Fault System 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, which transfer displacement between the mainly transform plate boundary of the Alpine ...

, which accommodates the transfer of displacement along the oblique convergent boundary between the

Indo-Australian Plate The Indo-Australian Plate is a major tectonic plate that includes the continent of Australia and the surrounding ocean and extends northwest to include the Indian subcontinent and the adjacent waters. It was formed by the fusion of the Indian an ...

and

Pacific Plate The Pacific Plate is an oceanic tectonic plate that lies beneath the Pacific Ocean. At , it is the largest tectonic plate. The plate first came into existence 190 million years ago, at the triple junction between the Farallon, Phoenix, and Iza ...

, from the

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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 ...

to the

Hikurangi Trench The Hikurangi Trench, also called the Hikurangi Trough, is an oceanic trench in the bed of the Pacific Ocean off the east coast of the North Island of New Zealand, lying between the southern end of the Cook Strait and the Chatham Rise. It is the ...

subduction zone.

Extent

The Hope Fault branches off from the Alpine Fault south of

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and then runs in a nearly straight line for about to the east coast of South Island just north of Kaikoura, with an offshore continuation of at least . It consists of several segments, from the southwest end, the Kelly Fault, then the Hurunui, Hope River, Conway and Seaward segments. It takes its name from the Hope River, which follows the trace of much of the Hope River segment.

Kelly Fault segment

The junction between the Hope fault and the Alpine Fault is complex. The Kelly Fault forms a major splay of the Hope Fault from just west of Harper Pass; it splays again to the west into the Newton and Hura faults. From repeat

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surveying on the region near

Arthur's Pass Arthur's Pass, previously called Camping Flat then Bealey Flats, and for some time officially Arthurs Pass, is a township in the Southern Alps of the South Island of New Zealand, located in the Selwyn district. It is a popular base for explorin ...

, the Kelly Fault marks a sharp reduction in velocities to the northwest of the Kelly and Hura faults.

Hurunui segment

This long segment runs from Harper pass to the junction of the Hope and Boyle rivers. The maximum slip-rate estimated from the offset of a stream is about /yr. A minimum slip-rate has also been estimated from offset of channels in a late Holocene

alluvial fan An alluvial fan is an accumulation of sediments that fans outwards from a concentrated source of sediments, such as a narrow canyon emerging from an escarpment. They are characteristic of mountainous terrain in arid to semiarid climates, but a ...

complex of /yr. The average recurrence interval for earthquake slip events on this segment is 310–490 yr.

Hope River segment

The Hope River segment runs about from the confluence of the Boyle and Hope rivers as far as the Hanmer Basin. From the offset of dated river terraces, a late Holocene horizontal slip-rate of about /yr and a vertical slip-rate of about 0.6 mm/yr have been calculated for this segment. The displacement is thought to have occurred by repeated slips which, if similar to that which caused the 1888 earthquake, indicate a

return period A return period, also known as a recurrence interval or repeat interval, is an average time or an estimated average time between events such as earthquakes, floods, landslides, or river discharge flows to occur. It is a statistical measurement typ ...

of about 140 years.

Conway segment

The Conway segment is the longest and straightest of the segments with a strike of about N73°E. It extends from the eastern part of the Hanmer Basin to just west of the junction with the Jordan Thrust near Kowhai River. The slip-rate for this segment, estimated from offset alluvial features, is about 23 mm/yr. The fault dips steeply to the northwest at about 70° and forms the southern termination of the Seaward Kaikoura, Hawk and Amuri ranges. This topography is a result of the significant component of reverse displacement on this fault zone. An average recurrence interval of 180–310 yr has been calculated for earthquakes along this segment.

Seaward segment

The Seaward segment extends from near the Kowhai River to the coast and has been recognised on the continental shelf from

seismic reflection Reflection seismology (or seismic reflection) is a method of exploration geophysics that uses the principles of seismology to estimate the properties of the Earth's subsurface from reflected seismic waves. The method requires a controlled seismi ...

data, extending for at least another . Part of this segment ruptured in the

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Hanmer Basin

Hanmer Basin is a small (10 x 20 km) pull-apart basin formed at the overlap between the Hope River and Conway segments of the Hope Fault. The right-stepping geometry of the offset between the two segments has caused local extension to occur and a basin to form. The

hot spring A hot spring, hydrothermal spring, or geothermal spring is a spring produced by the emergence of geothermally heated groundwater onto the surface of the Earth. The groundwater is heated either by shallow bodies of magma (molten rock) or by circ ...

s of

Hanmer Springs Hanmer Springs is a small town in the Canterbury region of the South Island of New Zealand. The Māori name for Hanmer Springs is Te Whakatakanga o te Ngārahu o te ahi a Tamatea, which means “where the ashes of Tamate’s (sic) fire lay� ...

are one of the results of the basin formation. Other smaller basins of similar type have formed at minor offsets along the Hope River segment. The basin began to form in the

Pleistocene The Pleistocene ( , often referred to as the ''Ice age'') is the geological Epoch (geology), epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fina ...

and contains more than 1000 m of sedimentary fill in the main

depocenter A depocenter or depocentre in geology is the part of a sedimentary basin where a particular rock unit has its maximum thickness. Depending on the controls on subsidence and the sedimentary environment the location of basin depocenters may vary wit ...

. The eastern end of the basin is currently being deformed by

transpression In geology, transpression is a type of strike-slip deformation that deviates from simple shear because of a simultaneous component of shortening perpendicular to the fault plane. This movement ends up resulting in oblique shear. It is generally v ...

associated with the southwestern end of the Conway segment. The destruction of the basin at its eastern end is matched by transtensional deformation at the western end that continues to enlarge the basin, giving rise to a roughly steady-state geometry. The basin fill is being constantly reworked as it is uplifted at the basin's eastern end and redeposited to the west.

History

The oldest fill in the Hanmer Basin is Pleistocene in age, which constrains the development of the Hope Fault to that period. The most recent earthquake on the Hope Fault was the

, which ruptured part of the Seaward segment. The previous earthquake was the 1888 North Canterbury earthquake, which ruptured the whole of the Hope River segment. Alexander McKay, a geologist working for the New Zealand geological survey, observed horizontal offsets in farm fences of between 1.5 and 2.6 metres along the fault. He was the first to associate a strike-slip displacement with an earthquake. The longest segment, the Conway segment, shows evidence of past earthquakes, although none have been recorded since European settlement in about 1850. Investigations show that at least three events have occurred, the most recent of which is dated to between 1720 and 1840.

Seismic hazard

All segments of the Hope Fault are likely to experience future earthquakes, the largest such events, a possible magnitude 7.5, would be expected from the Conway segment or the Jordan Thrust.

References

External links

Photo of displacement on the Hope Fault in 1888
at '' Te Ara: The Encyclopedia of New Zealand'' {{Seismic faults of New Zealand Seismic faults of New Zealand Active faults Strike-slip faults Fault, Hope