Awatere Fault
Encyclopedia
The Awatere 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 convergent boundary between the Indo-Australian Plate
and Pacific Plate
, from the transform Alpine Fault
to the Hikurangi Trench
subduction zone
.
The 1848 Marlborough earthquake
was caused by rupture of the whole of the eastern section of the Awatere Fault.
in the northeast. It is about 55 km in length and consists of several smaller segments. This section has an overall strike of N75–80°E, giving local zones of transtension
at some of the segment boundaries, such as at Isolated Flat.
follows the trace of much of the eastern section of the fault, giving its name to the whole structure.
of about 7.5 Mw. The rupture appears to have bypassed the Molesworth section of the fault, continuing on the southern strand through Barefell Pass.
Active fault
An active fault is a fault that is likely to have another earthquake sometime in the future. Faults are commonly considered to be active if there has been movement observed or evidence of seismic activity during the last 10,000 years....
dextral (right lateral) strike-slip fault in the northeastern part of South Island
South Island
The South Island is the larger of the two major islands of New Zealand, the other being the more populous North Island. It is bordered to the north by Cook Strait, to the west by the Tasman Sea, to the south and east by the Pacific Ocean...
, New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
. It forms part of the Marlborough Fault System
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 fault and the mainly destructive boundary of the...
, which accommodates the transfer of displacement along the oblique convergent boundary between the Indo-Australian Plate
Indo-Australian Plate
The Indo-Australian Plate is a major tectonic plate that includes the continent of Australia and surrounding ocean, and extends northwest to include the Indian subcontinent and adjacent waters...
and Pacific Plate
Pacific Plate
The Pacific Plate is an oceanic tectonic plate that lies beneath the Pacific Ocean. At 103 million square kilometres, it is the largest tectonic plate....
, from the transform Alpine Fault
Alpine Fault
The Alpine Fault is a geological fault, more specifically known as a right-lateral strike-slip fault, that runs almost the entire length of New Zealand's South Island. It forms a transform boundary between the Pacific Plate and the Indo-Australian Plate. Earthquakes along the fault, and the...
to the Hikurangi Trench
Hikurangi Trench
The Hikurangi Trench is a linear deep in 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. Though much shallower, it is the southward continuation of the Kermadec Trench and forms part of the...
subduction zone
Subduction
In geology, subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle, as the plates converge. These 3D regions of mantle downwellings are known as "Subduction Zones"...
.
The 1848 Marlborough earthquake
1848 Marlborough earthquake
The 1848 Marlborough earthquake is the name associated with a severe earthquake which occurred at 1:40 a.m. on 16 October 1848 and whose epicenter was in the Marlborough region of the South Island of New Zealand....
was caused by rupture of the whole of the eastern section of the Awatere Fault.
Extent
The 175 km long Awatere Fault is formed of two main segments; the Molesworth section to the southwest and the Eastern section to the northeast. A further strand links the southwestern end of the Eastern section to the Clarence Fault, passing through Barefell Pass.Molesworth section
The Molesworth segment of the Awatere Fault runs from close to the junction between the Alpine and Wairau Faults near Lake Tennyson, to near Molesworth StationMolesworth Station
Molesworth Station is New Zealand's largest farm, at over 1,800 km², and supports the country's biggest herd of cattle. It also hosts government science programs, such as research into bovine tuberculosis and related research into possums....
in the northeast. It is about 55 km in length and consists of several smaller segments. This section has an overall strike of N75–80°E, giving local zones of transtension
Transtension
Transtension is the term used to describe a rock mass or area of the Earth's crust that experiences both extensive and transtensive shear. As such, transtensional regions are characterised by both extensional structures and wrench structures ....
at some of the segment boundaries, such as at Isolated Flat.
Eastern section
The Eastern section of the fault runs from Molesworth Station to the coast, near White Bluffs, without significant segmentation. The Awatere RiverAwatere 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...
follows the trace of much of the eastern section of the fault, giving its name to the whole structure.
Recent seismicity
The Molesworth section appear to have moved twice since about 3000 years ago, in events with slip values of about 6–7 m. Trenching at Saxton River at the eastern end of the Molesworth section suggests 8 ruptures since about 6,300 years ago, with an estimated mean recurrence of about 800 years. Evidence from the eastern section of the fault suggests that there were 9–10 earthquakes in the period from 8610 BP to AD 1848. This gives a mean recurrence interval of 820–950 years. In 1848 a minimum 105 km length section of the fault ruptured, causing an earthquake of an estimated magnitudeMoment magnitude scale
The moment magnitude scale is used by seismologists to measure the size of earthquakes in terms of the energy released. The magnitude is based on the seismic moment of the earthquake, which is equal to the rigidity of the Earth multiplied by the average amount of slip on the fault and the size of...
of about 7.5 Mw. The rupture appears to have bypassed the Molesworth section of the fault, continuing on the southern strand through Barefell Pass.