New Hebrides Trench

{{Short description|Oceanic trench in the southern Pacific Ocean}} {{Annotated image | image = Unlabelled Zealandia topographic map.jpg | image-width = 1024  | image-left = -280 | image-top = -0 | width = 400 | height = 280 | float = right | annotations = {{Annotation |304|10|Fiji| text-align=right | font-size=16 | font-weight=normal| font-family=Arial | background-color=| color=}} {{Annotation |122|70|Vanuatu| text-align=right | font-size=16 | font-weight=normal| font-family=Arial | background-color=| color=}} {{Annotation |20|150|New Caledonia| text-align=left | font-size=16 | font-weight=normal| font-family=Arial | background-color=| color=}} {{Annotation |10|210|{{colored link|#FFFFFF|Zealandia|Zealandia}}| text-align=left | font-size=12 | font-weight=bold| font-family=Arial | background-color=| color=}} {{Annotation |200|60|{{colored link|#FFFFFF|North Fiji Basin|North  Fiji Basin}}| text-align=left | font-size=12 | font-weight=bold| font-family=Arial | background-color=| color=}} {{Annotation |2|20|{{colored link|#FFFFFF|d'Entrecasteaux Ridge|d'Entrecasteaux     Ridge}}| text-align=left | font-size=12 | font-weight=bold| font-family=Arial | background-color=| color=}} {{Annotation |166|188|{{colored link|#000000|New Hebrides Trench|New Hebrides   Trench}}| text-align=left | font-size=14 | font-weight=normal| font-family=Arial | background-color=| color=}} {{Annotation |270|110|{{colored link|#FFFFFF|Hunter fracture zone|  Hunter Fracture     Zone}}| text-align=left | font-size=12 | font-weight=bold| font-family=Arial | background-color=| color=}} {{Annotation |360|104|{{colored link|#FFFFFF|Lau-Colville Ridge|    Lau   Ridge}}| text-align=left | font-size=12 | font-weight=bold| font-family=Arial | background-color=| color=}} {{Annotation |258|235|{{colored link|#FFFFFF|South Fiji Basin|South   Fiji Basin}}| text-align=left | font-size=12 | font-weight=bold| font-family=Arial | background-color=| color=}} {{Annotation |200|140|{{colored link|#FFFFFF|Hunter Ridge|Hunter Ridge}}| text-align=left | font-size=12 | font-weight=bold| font-family=Arial | background-color=| color= }} {{Annotation |280|175|{{colored link|#FFFFFF|South Fiji Basin|Minerva Abyssal   Plain}}| text-align=left | font-size=12 | font-weight=bold| font-family=Arial | background-color=| color=}} {{Annotation |180|240|{{colored link|#FFFFFF|Cook fracture zone |   Cook fracture   zone}}| text-align=left | font-size=12 | font-weight=bold| font-family=Arial | background-color=| color=}} {{Annotation |80|220|{{colored link|#FFFFFF|Norfolk Ridge|Norfolk  Ridge}}| text-align=left | font-size=12 | font-weight=bold| font-family=Arial | background-color=| color=}} {{Annotation |140|220|{{colored link|#FFFFFF|Loyalty Islands Province|Loyalty Ridge}}| text-align=left | font-size=12 | font-weight=bold| font-family=Arial | background-color=| color=}} |caption =Geographical and geological relationships of the New Hebrides Trench in the central and southern Vanuatu subduction zone. Subduction is towards the north east and this map does not show the North New Hebrides (Torres) Trench. Zealandia is outlined in black. }} {{maplink|frame=yes|frame-align=right|frame-width=260|frame-height=150|frame-long=172|frame-lat=-20.5|zoom=4|raw={{Wikipedia:Map data/Vanuatu subduction zone}} |text=Approximate surface projection on Pacific Ocean of New Hebrides Trench (dark blue). }} 260px|thumb|right|Map of the New Hebrides Trench and surrounding tectonic plates

The '''New Hebrides Trench''' (perhaps better termed the '''South New Hebrides Trench''')<ref>[https://www.ngdc.noaa.gov/gazetteer/ GEBCO:Hebrides]</ref><ref name="MG">[https://marineregions.org/gazetteer.php?p=details&id=7361 Marine Gazetteer:South New Hebrides Trench]</ref> is an oceanic trench which is over {{convert|7.1|km|abbr=on}} deep in the Southern Pacific Ocean.<ref>{{Harvnb|Linley|Stewart|McMillan|Clark|2017|loc=Section:2.1. Study sites}}</ref> It lies to the northeast of New Caledonia and the Loyalty Islands, to the southwest of Vanuatu (formerly known as the New Hebrides), east of Australia, and south of Papua New Guinea and the Solomon Islands. The trench was formed as a result of a subduction zone. The Australian plate is being subducted under the New Hebrides plate causing volcanism which produced the Vanuatu archipelago.

The trench was first described in 1962 by the U.S. research vessel "Spencer F. Baird", in the Scripps Institution of Oceanography Proa Expedition<ref name="MG"/> and was explored in more detail in 2013 by the University of Aberdeen's Oceanlab team. They found cusk-eels, prawns, and other eels, and crustaceans. This is significantly different from other deep sea trenches that have been studied.<ref>{{cite news |last1=Morelle |first1=Rebecca |author-link=Rebecca Morelle |title=New Hebrides trench: First look at unexplored deep sea |url=https://www.bbc.com/news/science-environment-26373896 |access-date=25 January 2022 |publisher=BBC News |date=3 March 2014}}</ref>

==Geography== The southern New Hebrides Trench is defined as extending from {{coord|-17.75|167.3333|format=dms|display=inline}} to {{coord|-23.1333|174.1667|format=dms|display=inline}}.<ref name="MG"/> The North New Hebrides Trench (Torres Trench) that extends to the west of the Solomon Islands is a separate marine feature to the southern New Hebrides Trench due to the d'Entrecasteaux Ridge, even though they are tectonically part of the same subduction zone.

== Tectonics == At the New Hebrides Trench, the Australian plate is being subducted underneath the New Hebrides microplate in the Vanuatu subduction zone (previously called the New Hebrides subduction zone) towards the east where the trench has a north–south orientation. The trench is to the northeast of the Zealandia continental margin. The convergence rate in the subduction zone ranges from {{cvt|120|mm}}/yr in the south, to {{cvt|40|mm}}/yr in the central section, to the high rate of {{cvt|170|mm}}/yr in the north at about latitude 11°S in the Solomon Island region north of the Torres.<ref name="Roger2023S">{{Harvnb|Roger|Pelletier|Gusman|Power|2023|loc=Section:2 Seismotectonic context}}</ref> The anomalous lack of convergence in the central section is caused by the subduction of the d'Entrecasteaux Ridge. The progressive subduction/collision of the NW–SE trending Loyalty Ridge located on the Australian plate under the southern Vanuatu microplates produces much earthquake activity<ref name="Roger2023S"/> but the most southernmost part of the trench south of latitude 22.5° S and east of longitude 170° E is not as highly tectonically active<ref name="Roger2023A">{{Harvnb|Roger|Pelletier|Gusman|Power|2023|loc=Section:Abstract}}</ref> It has been suggested that the current northern subduction to the south of the bend to the east in the trench should be considered as a separate subduction zone, called the Matthew and Hunter subduction system or subduction zone given its immature current volcanic arc and other characteristics.<ref>{{Harvnb|Patriat|Falloon|Danyushevsky|Collot|2019|loc=The Matthew and Hunter area: a recently discovered infant subduction zone}}</ref><ref>{{Harvnb|McCarthy|Falloon|Danyushevsky|Sauermilch|2022|loc=2.1. The Vanuatu – Hunter Ridge subduction system}}</ref> It translates into the non subducting Hunter fracture zone which is a transform faulting fracture zone.<ref name="Durance2012p915">{{Harvnb|Durance|Jadamec|Falloon|Nicholls|2012|loc=p915}}</ref> From 3 million years ago the southernmost Central Spreading Ridge of the North Fiji Basin propagated southward and has now intersected with the New Hebrides Trench and the Hunter fracture zone to form a triple junction with the Conway Reef plate.<ref name="Durance2012p915"/> ==Associated seismicity== The area of the southern part of the subduction zone between the latitudes 21.5 and 22.5° S and the longitudes 169 and 170° E is very active.<ref name="Roger2023S"/> There have been multiple earthquakes including swarms of magnitude Mw 7.0+ during recent decades impacting on New Caledonia and Vanuatu.<ref name="Roger2023S"/> The strain accumulation is regularly partially released through moderate to strong earthquakes during sequences which have included both interplate thrust faulting earthquakes and outer rise normal faulting earthquakes west and south-west of the trench.<ref name="Roger2023S"/>

The {{M|w|7.7}} 2021 Loyalty Islands earthquake (Matthew Island earthquake) was much stronger than the usual seismicity on the southernmost aspects of the trench.<ref name="Roger2023E">{{Harvnb|Roger|Pelletier|Gusman|Power|2023|loc=3.1 The earthquake}}</ref> The epicenter was close to Matthew Island, and was both preceded and followed by a seismic crisis of multiple events with greater than {{M|w|5.0}}<ref name="Roger2023E"/>

===Major earthquakes associated with the subduction zone=== The table below shows only earthquakes greater than {{M|w|7.5|link=yes}} or significant earthquakes that are not in the list of earthquakes in Vanuatu and list of earthquakes in the Solomon Islands archipelago for geographical reasons.<ref name="Map of Magnitude 7.5+ earthquakes in the Area">{{cite web |title=Map of Magnitude 7.5+ along the New Hebrides Trench and Surrounding Areas. |url=https://earthquake.usgs.gov/earthquakes/map/?currentFeatureId=iscgem16957737&extent=-30.63791,149.32617&extent=-1.09857,202.76367&range=search&timeZone=utc&search=%7B%22name%22:%22Search%20Results%22,%22params%22:%7B%22starttime%22:%221622-01-16%2000:00:00%22,%22endtime%22:%222022-01-23%2023:59:59%22,%22maxlatitude%22:-9.667,%22minlatitude%22:-24.088,%22maxlongitude%22:173.232,%22minlongitude%22:163.916,%22minmagnitude%22:7.5,%22orderby%22:%22time%22%7D%7D |publisher=United States Geological Survey |access-date=25 January 2022}}</ref><ref name="Ioualalen2017">{{cite journal |last1=Ioualalen |first1=Mansour |title=Investigating the March 28th 1875 and the September 20th 1920 earthquakes/tsunamis of the Southern Vanuatu arc, offshore Loyalty Islands, New Caledonia |journal= Tectonophysics|date=May 2017 |volume=709 |page=20 |doi=10.1016/j.tecto.2017.05.006 |bibcode=2017Tectp.709...20I }}</ref>

{| class="wikitable" |- ! Article ! Date ! Location ! Magnitude ({{M|w|link=yes}}) |- | - |{{center|March 28, 1875}} |{{center|Loyalty Islands}} |{{center|8.1-8.2<ref name="Ioualalen2017"/>}} |- | - |{{center|August 9, 1901}} |{{center|Tadine, New Caledonia}} |{{center|7.9<ref name="Roger2023S"/>}} |- | - |{{center|June 16, 1910}} |{{center|Isangel, Vanuatu}} |{{center|7.8}} |- | - |{{center|September 20, 1920}} |{{center|Isangel, Vanuatu}} |{{center|7.9<ref name="Ioualalen2017"/>}} |- | - |{{center|August 25, 1926}} |{{center|Southern Vanuata Subduction Zone}} |{{center|7.0<ref name="Roger2023S"/>}} |- | - |{{center|December 2, 1950}} |{{center|Port-Vila, Vanuatu}} |{{center|7.9<ref name="Roger2023S"/>}} |- | - |{{center|December 17, 1957}} |{{center|Sola, Vanuatu}} |{{center|7.8}} |- | - |{{center|August 11, 1965}} |{{center|Central Vanuata Subduction Zone}} |{{center|7.6<ref name="Roger2023S"/>}} |- | - |{{center|December 31, 1966}} |{{center|Lata, Solomon Islands}} |{{center|7.8}} |- | - |{{center|July 17, 1980}} |{{center|Lata, Solomon Islands}} |{{center|7.9}} |- |2009 Vanuatu earthquakes |{{center|October 7, 2009}} |{{center|Sola, Vanuatu}} |{{center|7.8<ref name="Roger2023S"/>}} |- |2013 Solomon Islands earthquake |{{center|February 6, 2013}} |{{center|Lata, Solomon Islands}} |{{center|8.0<ref name="Roger2023S"/>}} |- |2021 Loyalty Islands earthquake (Matthew Island earthquake) |{{center|February 10, 2021}} |{{center|Southeast of the Loyalty Islands}} |{{center|7.7<ref name="Roger2023G">{{Harvnb|Roger|Pelletier|Gusman|Power|2023|loc=Section:1.1 Generalities}}</ref>}} |- | - |{{center|March 30, 2022}} |{{center|Loyalty Islands fore-shock by 8 hours to the March 31 earthquake}} |{{center|6.9<ref name="Roger2023S"/>}} |- | - |{{center|March 31, 2022}} |{{center|Loyalty Islands {{convert|279|km|abbr=on}} southeast of Maré Island}} |{{center|7.0<ref name="Roger2023S"/>}} |- | - |{{center|May 19, 2023}} |{{center|Loyalty Islands {{convert|339|km|abbr=on}} east of Isle of Pines}} |{{center|7.7}} |- |2024 Port Vila earthquake |{{center|December 17, 2024}} |{{center|Vanuatu {{convert|30|km|abbr=on}} east of Port-Vila}} |{{center|7.3<ref>{{cite web|publisher=United States Geological Survey|url=https://earthquake.usgs.gov/earthquakes/eventpage/us7000nzf3/executive|title=M 7.3 - 30 km W of Port-Vila, Vanuatu |date=17 December 2024|access-date=17 December 2024}}</ref>}} |} {{clear}}

==Tsunami risk== The region could trigger tsunamis with a main propagation axis striking from WSW–ENE (putting New Caledonia and south Vanuatu most at risk) to S–N (putting northern New Zealand and Vanuatu most at risk).<ref name="Roger2023S"/> The 5 December 2018 {{M|w|7.5}} normal faulting earthquake generated a tsunami of more than {{convert|2|m|abbr=on}} in southern New Caledonia and Vanuatu.<ref name="Roger2023S"/>

==Ecology== The trench seawater has a temperature of about {{convert|2|C}} from {{convert|2|km}} to {{convert|6|km}} depth.<ref>{{Harvnb|Linley|Stewart|McMillan|Clark|2017|loc=Section:3.1. Environmental characteristics, Fig. 2}}</ref> Fish species known include those from the genus Pachycara (e.g. ''Pachycara moelleri'' at {{convert|4|km}} depth), ''Ilyophis robinsae'' or large Synaphobranchid, ''Synaphobranchus brevidorsalis'', ''Hydrolagus'' spp., ''Bathyraja'' spp., ''Bassozetus'' spp., ''Antimora rostrata'' multiple species of ''Coryphaenoides'', members of the Zoarcidae family and members of the family Alepocephalidae.<ref name="Linley2017S">{{Harvnb|Linley|Stewart|McMillan|Clark|2017|loc=3.2. Species diversity, Table 1}}</ref> For some reason, although well known in surrounding nearby waters, Macrourids are absent from the northern New Hebrides Trench.<ref name="Linley2017M">{{Harvnb|Linley|Stewart|McMillan|Clark|2017|loc=4.1. Macrourid or ophidiid dominated communities}}</ref> This is believed to be because the ecosystem characteristics allow the low-energy ophidiid to dominate.<ref name="Linley2017M"/> Amongst crustaceans, amphipods including members of the family Lysianassidae, prawns of the genus Benthesicymus (''Benthesicymus crenatus'', ''Benthesicymus howensis'') and Aristeidae (''Cerataspis monstrosus'') and Oplophoridae shimp (''Acanthephyra tenuipes'' and ''Heterogenys microphthalma'') were found.<ref>{{cite journal|last1=Swan |first1=Ja|last2=Jamieson |first2=AJ|last3= Linley |first3=TD|last4=Yancey|first4=PH|title= Worldwide distribution and depth limits of decapod crustaceans (Penaeoidea, Oplophoroidea) across the abyssal-hadal transition zone of eleven subduction trenches and five additional deep-sea features|journal=Journal of Crustacean Biology|date=4 February 2021|volume=41|issue=1|doi=10.1093/jcbiol/ruaa102|url=https://academic.oup.com/jcb/article/41/1/ruaa102/6128500?itm_medium=sidebar&itm_source=trendmd-widget&itm_campaign=Journal_of_Crustacean_Biology&itm_content=Journal_of_Crustacean_Biology_0|doi-access=free}}</ref>

== References == {{reflist}}

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Category:Seismic zones of Oceania Category:Seismic faults of Oceania Category:Geology of New Caledonia Category:Geology of the Pacific Ocean Category:Loyalty Islands Category:Oceanic trenches of the Pacific Ocean Category:Subduction zones