Hikurangi Margin | |
---|---|
Hikurangi Subduction Zone | |
Etymology | Hikurangi |
Country | New Zealand |
Region | North Island |
Characteristics | |
Length | 300 km (190 mi) |
Displacement | 6 cm (2.4 in)/yr |
Tectonics | |
Plate | Indo-Australian |
Status | Active |
Earthquakes | Mw 8.2 |
Type | Subduction |
Age | Miocene-Holocene |
New Zealand geology database (includes faults) |
The Hikurangi Margin (also known as the Hikurangi Subduction Zone) is New Zealand's largest subduction zone and fault. [1]
The Hikurangi Subduction Zone is an active subduction zone extending off the east coast of New Zealand's North Island, where the Pacific and Australian plates collide. [2] [3] The subduction zone where the Pacific Plate goes under the Kermadec Plate offshore of Gisborne accommodates approximately 6 cm/year (2.4 in/year) of plate movement while off the Wairarapa shore this decreases to perhaps as low as 2 cm/year (0.79 in/year). [1] It is the southern portion of the Tonga–Kermadec–Hikurangi subduction zone and its main feature is the Hikurangi Trench. The tectonics of this area can be most easily resolved by postulating between the Havre Trough to the east of the South Kermadec Ridge Seamounts, the Whakatane Graben and the Taupo Volcanic Zone on the North Island of New Zealand there is a continuation of the Tonga micro-plate into the Kermadec microplate which probably extends to Cook Strait. [4] The on land active fault systems would be consistent with the Kermadec Plate's unclear south western boundary being the North Island Fault System. The Kermadec Plate - Pacific Plate eastern boundary is the Hikurangi-Kermadec trench. [4]
The Hikurangi Plateau, a remnant of a large igneous province is being subducted under the North Island at the margin currently. The subducting slab's Wadati–Benioff zone is over 200 km (120 mi) deep at Tauranga and Mount Taranaki and more than 75 km (47 mi) deep under the Taupō Volcanic Zone. [5]
Earthquakes of up to Mw 8.2 have been recorded on the Hikurangi Margin, generating local tsunamis, and earthquakes in the 9.0M range are thought to be possible. [6] The Ruatoria debris avalanche originated on the north part of the subduction zone and probably occurred around 170,000 years ago. [7] Multiple uplift earthquakes will have occurred in the locked areas of the fault but a good historical record does not yet exist.
There are well characterised now slow slip events across the Hikurangi Margin [1] Hikurangi Margin slow slip events occur up to yearly at a shallow depth of less than 10 km (6.2 mi), and last for up to 6 weeks relieving stress on much of the fault. [8] For example the series of slow slip events between 2013-2016 involved moment release of approximately Mw 7.4. [9] At least one of the well characterised events was very close to the trench. [10] On land parallel to the predicted fault line of the Hikurangi Margin are active faults which are not fully characterised and include the Parkhill Fault Zone near Cape Kidnappers, the Maraetotara Fault Zone, and the Flat Point Fault. The slow slip activity has been associated with on land a mud volcano eruption causing a significant landslip. [11]
Because it has been possible to examine the mechanical properties of the subducted ocean floor clays recovered by drilling into the subducted rock, it has been possible to develop a model that may explain both the slow slip events but also why large and relatively deep earthquake ruptures are propagated into the shallow areas of the subduction zone thus displacing the ocean floor and generating tsunamis. [12] The model suggests that shallow-depth subducted water-saturated clay-rich sediments, promote earthquake rupture propagation and slip. [12]
The Hikurangi Margin has the potential to produce notable earthquakes. Some significant earthquakes are:
There have been ten possible large subduction earthquakes identified over the past 7000 years before the above historic records along the Hikurangi margin. [16] The last such pre history earthquake occurred 568 ± 25 [16] years ago in the southern Hikurangi margin. [17] An earthquake associated with a tsunami and at least 354 km (220 mi) of the margin rupturing, occurred between 943 and 888years ago. [17]
The Ring of Fire is a tectonic belt, about 40,000 km (25,000 mi) long and up to about 500 km (310 mi) wide, which circumscribes the Pacific Ocean. It contains between 750 and 915 volcanoes, around two-thirds of the world total, and 90% of the world's earthquakes, including 81% of its largest, take place within the belt.
The Japan Trench is an oceanic trench part of the Pacific Ring of Fire off northeast Japan. It extends from the Kuril Islands to the northern end of the Izu Islands, and is 8,046 metres (26,398 ft) at its deepest. It links the Kuril–Kamchatka Trench to the north and the Izu–Ogasawara Trench to its south with a length of 800 kilometres (497 mi). This trench is created as the oceanic Pacific plate subducts beneath the continental Okhotsk Plate. The subduction process causes bending of the down going plate, creating a deep trench. Continuing movement on the subduction zone associated with the Japan Trench is one of the main causes of tsunamis and earthquakes in northern Japan, including the megathrust Tōhoku earthquake and resulting tsunami that occurred on 11 March 2011. The rate of subduction associated with the Japan Trench has been recorded at about 7.9–9.2 centimetres (3.1–3.6 in)/yr.
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The Hikurangi Plateau is an oceanic plateau in the South Pacific Ocean east of the North Island of New Zealand. It is part of a large igneous province (LIP) together with Manihiki and Ontong Java, now located 3,000 km (1,900 mi) and 3,500 km (2,200 mi) north of Hikurangi respectively. Mount Hikurangi, in Māori mythology the first part of the North Island to emerge from the ocean, gave its name to the plateau.
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The 1843 Whanganui earthquake occurred on 8 July at 16:45 local time with an estimated magnitude of 7.5 on the Mw scale. The maximum perceived intensity was IX (Violent) on the Mercalli intensity scale, and possibly reaching X (Extreme). The epicentre is estimated to have been within a zone extending 50 km northeast from Whanganui towards Taihape. GNS Science has this earthquake catalogued and places the epicentre 35 km east of Taihape, near the border of Hawke's Bay. This was the first earthquake in New Zealand over magnitude 7 for which written records exist, and the first for which deaths were recorded.
The 1995 Antofagasta earthquake occurred on July 30 at 05:11 UTC with a moment magnitude of 8.0 and a maximum Mercalli intensity of VII. The Antofagasta Region in Chile was affected by a moderate tsunami, with three people killed, 58 or 59 injured, and around 600 homeless. Total damage from the earthquake and tsunami amounted to $1.791 million.
The North Island Fault System (NIFS) is a set of southwest–northeast trending seismically-active faults in the North Island of New Zealand that carry much of the dextral strike-slip component of the oblique convergence of the Pacific Plate with the Australian Plate. However despite at least 3 km (1.9 mi) of uplift of the axial ranges in the middle regions of the fault system during the last 10 million years most of the shortening on this part of the Hikurangi Margin is accommodated by subduction.
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The 2014 Eketāhuna earthquake struck at 3:52 pm on 20 January, centred 15 km east of Eketāhuna in the south-east of New Zealand's North Island. It had a maximum perceived intensity of VII on the Mercalli intensity scale. Originally reported as magnitude 6.6 on the Richter Scale, the earthquake was later downgraded to a magnitude of 6.2. A total of 1112 aftershocks were recorded, ranging between magnitudes 2.0 and 4.9 on the Richter Scale.
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The 1904 Cape Turnagain earthquake struck 10 kilometres (6.2 mi) north of Cape Turnagain on the morning of 9 August with a magnitude estimated at 6.8 Ms and 7.0–7.2 Mw It was felt throughout the North Island and upper South Island, with many communities within a 500 kilometres (310 mi) radius reporting noticeable ground shaking. Heavy damage occurred to the landscape and personal property and one man died. It was the largest to strike New Zealand since the 7.0 Mw North Canterbury earthquake in 1888.
Laura Martin Wallace is a geodetic principal scientist who works between the University of Texas at Austin and GNS Science in New Zealand. She was elected Fellow of the Royal Society Te Apārangi in 2018.
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The Hikurangi subduction zone (sometimes referred to as the Hikurangi subduction margin) is New Zealand's largest fault
Hikurangi Margin slow slip events occur every 1-2 years at a shallow depth (<10km), and last for 2-6 weeks