Hikurangi Margin

The Hikurangi Margin (also known as the Hikurangi Subduction Zone) is New Zealand's largest subduction zone and fault.[1]

Hikurangi Margin
Hikurangi Subduction Zone
The Hikurangi Margin is an active fault off the east coast of the North Island of New Zealand. This shows variation in displacement vector of Pacific Plate relative to the Kermadec Plate and Australian Plate along the boundary. The Kermadec Trench label would better read Hikurangi Trench at this position. The Kermadec Plate is not labelled but lies between the labels of the North Island Fault System and the Kermadec Trench in the picture.
The relationship of the Kermadec Plate to its New Zealand portion whose eastern margin is the Hikurangi Subduction Zone and the Tonga Plate.
EtymologyHikurangi
CountryNew Zealand
RegionNorth Island
Characteristics
Length300 km (190 mi)
Displacement6 cm (2.4 in)/yr
Tectonics
PlateIndo-Australian
StatusActive
EarthquakesMw8.2
TypeSubduction
AgeMiocene-Holocene
New Zealand geology database (includes faults)

Tectonics

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

Earthquakes of up to Mw8.2 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.

Slow slip events

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]

Modelling events

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]

Risk

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 888 years ago.[17]

References
  1. Wallace, Laura; Clark, Kate (29 November 2017). "Hikurangi subduction zone - GeoNet: News". GeoNet. GNS Science. Retrieved 29 August 2022. The Hikurangi subduction zone (sometimes referred to as the Hikurangi subduction margin) is New Zealand's largest fault
  2. Clark et al. 2019, Introduction
  3. "Hikurangi Margin". The University of Waikato. Archived from the original on 29 January 2015. Retrieved 19 May 2015.
  4. Bird, Peter (2003). "An updated digital model of plate boundaries". Geochemistry, Geophysics, Geosystems. 4 (3): 1027. Bibcode:2003GGG.....4.1027B. doi:10.1029/2001GC000252. S2CID 9127133.
  5. Clark et al. 2019, Figure 1
  6. Wallace, Laura M.; Cochran, Ursula A. (June 2014). "Earthquake and Tsunami Potential of the Hikurangi Subduction Thrust, New Zealand: Insights from Paleoseismology, GPS, and Tsunami Modeling". Oceanography. 27 (2): 104–117. doi:10.5670/oceanog.2014.46.
  7. Collot, John-Yves (10 September 2001). "The giant Ruatoria debris avalanche on the northern Hikurangi margin, New Zealand: Result of oblique seamount subduction" (PDF). Journal of Geophysical Research: Solid Earth. 106 (B9): 19, 271–19, 297. Bibcode:2001JGR...10619271C. doi:10.1029/2001JB900004.
  8. "Slow Slip Watch:Hikurangi". GeoNet. GNS Science. 2022. Retrieved 29 August 2022. Hikurangi Margin slow slip events occur every 1-2 years at a shallow depth (<10km), and last for 2-6 weeks
  9. Woods, Katherine; Wallace, Laura; Hamling, Ian; Savage, Martha; Williams, Charles (2021). Assessing the interplay between deep subduction interface slow slip events and large local earthquakes at the Hikurangi subduction zone, New Zealand. AGU Fall Meeting. Bibcode:2021AGUFM.G25B0364W. Retrieved 29 August 2022.
  10. Wallace, LM; Webb, SC; Ito, Y; Mochizuki, K; Hino, R; Henrys, S; Schwartz, SY; Sheehan, AF (2016). "Slow slip near the trench at the Hikurangi subduction zone, New Zealand". Science. 352 (6286): 701–4. Bibcode:2016Sci...352..701W. doi:10.1126/science.aaf2349. PMID 27151867. S2CID 206647253.
  11. Leighton, Alex; Brook, Martin S.; Cave, Murry; Rowe, Michael C.; Stanley, Alec; Tunnicliffe, Jon F. (2022). "Engineering geomorphological reconnaissance of the December 2018 Waimata Valley mud volcano eruption, Gisborne, New Zealand". Quarterly Journal of Engineering Geology and Hydrogeology. 55 (4). Bibcode:2022QJEGH..55..149L. doi:10.1144/qjegh2021-149.
  12. Aretusini, S; Meneghini, F; Spagnuolo, E; Harbord, CW; Di Toro, G (2021). "Fluid pressurisation and earthquake propagation in the Hikurangi subduction zone". Nature Communications. 12 (2481): 2481. doi:10.1038/s41467-021-22805-w. hdl:11577/3400836. PMC 8087711. PMID 33931641.
  13. Downes, G; Barberopoulou, A; Cochran, U; Clark, K; Scheele, F (2017). "The New Zealand Tsunami Database: Historical and Modern Records:Source Event 70, 26/03/1947, 8:32:00 am". Seismological Research Letters. 88 (2): 342-353. doi:10.1785/0220160135.
  14. "M 7.4 Hawke's Bay Tue, Feb 3 1931". GeoNet. Retrieved 29 August 2022.
  15. "Story:M 7.4 Hawke's Bay Tue, Feb 3 1931". www.geonet.org.nz. GNS Science. Retrieved 29 August 2022.
  16. Clark et al. 2019, Abstract
  17. Clark et al. 2019, Table 3, Figure 12
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