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The Sunda Trench, earlier known as and sometimes still indicated as the Java Trench,^[1] is an oceanic trench located in the Indian Ocean near Sumatra, formed where the Australian-Capricorn plates subduct under a part of the Eurasian plate. It is 3,200 kilometres (2,000 mi) long with a maximum depth of 7,290 metres (23,920 feet).^[2] Its maximum depth is the deepest point in the Indian Ocean. The trench stretches from the Lesser Sunda Islands past Java, around the southern coast of Sumatra to the Andaman Islands, and forms the boundary between the Indo-Australian plate and Eurasian plate (more specifically, Sunda plate). The trench is considered to be part of the Alpide belt as well as one of oceanic trenches around the northern edges of the Australian plate.

In 2005, scientists found evidence that the 2004 earthquake activity in the area of the Java Trench could lead to further catastrophic shifting within a relatively short period, perhaps less than a decade.^[3] This threat has resulted in international agreements to establish a tsunami warning system in place along the Indian Ocean coast.^[4]

Characteristics

For about half its length, off of Sumatra, it is divided into two parallel troughs by an underwater ridge, and much of the trench is at least partially filled with sediments. Mappings after the 2004 Indian Ocean earthquake of the plate boundary showed a resemblance to suspension bridge cables, with peaks and sags, indicative of asperity and locked faults, instead of the traditional wedge shape expected.^[5]

Exploration

Some of the earliest explorations of the trench occurred in the late 1950s when Robert L. Fisher, a research geologist at the Scripps Institution of Oceanography, investigated the trench as part of a worldwide scientific field exploration of the world's ocean floor and sub-oceanic crustal structure. Bomb-sounding, echo-train analysis, and manometer were some of the techniques used to determine the depth of the trench. The research contributed to an understanding of the subduction characteristic of the Pacific margins.^[6] Various agencies have explored the trench in the aftermath of the 2004 earthquake, and these explorations have revealed extensive changes in the ocean floor.^[7]

Crewed descent

On 5 April 2019 Victor Vescovo made the first crewed descent to the deepest point of the trench in the Deep-Submergence Vehicle Limiting Factor (a Triton 36000/2 model submersible) and measured a depth of 7,192 m (23,596 ft) ±13 m (43 ft) by direct CTD pressure measurements at 11°7'44" S, 114°56'30" E,^[8]^[9] about 500 km (310 miles) south of Bali. The operating area was surveyed by the support ship, the Deep Submersible Support Vessel DSSV Pressure Drop, with a Kongsberg SIMRAD EM124 multibeam echosounder system. The gathered data was donated to the GEBCO Seabed 2030 initiative.^[10]^[11] The dive was part of the Five Deeps Expedition. The objective of this expedition is to thoroughly map and visit the deepest points of all five of the world's oceans by the end of September 2019.^[12]

To resolve the debate regarding the deepest point of the Indian Ocean, the Diamantina fracture zone was surveyed by the Five Deeps Expedition in March 2019, recording a maximum water depth of 7,019 m (23,028 ft) ±17 m (56 ft) at 33°37'52" S, 101°21'14" E for the Dordrecht Deep.^[8] This confirmed that the Sunda Trench was indeed deeper than the deepest location in the Diamantina Fracture Zone.^[13]

Associated seismicity

The subduction of the Indo-Australian plate beneath a bloc of the Eurasian plate is associated with numerous earthquakes. Several of these earthquakes are notable for their size, associated tsunamis, and/or the number of fatalities they caused.

Sumatra segment

1797 Sumatra earthquake: magnitude 8.6–8.8
1833 Sumatra earthquake: magnitude 8.8–9.2
1861 Sumatra earthquake: magnitude ~8.5
1935 Sumatra earthquake: magnitude 7.7
2000 Enggano earthquake: magnitude 7.9
2002 Sumatra earthquake: A magnitude 7.3 earthquake that occurred at the boundary between the rupture areas of the 2004 and 2005 earthquakes listed below.
2004 Indian Ocean earthquake and tsunami: Mw 9.2–9.3
2005 Nias–Simeulue earthquake: magnitude 8.6
2007 Bengkulu earthquakes: Series of earthquakes, the three largest were magnitude 8.5, 7.9, and 7.0.
2008 Simeulue earthquake: magnitude 7.4 near the 2002 event.
2009 Sumatra earthquakes: magnitude 7.6
2010 Mentawai earthquake and tsunami: magnitude 7.8

Java segment

1917 Bali earthquake: magnitude 6.6
1994 Java earthquake: magnitude 7.8
2006 Pangandaran earthquake and tsunami: magnitude 7.7
2009 West Java earthquake: magnitude 7.0
2019 Sunda Strait earthquake: magnitude 6.9

References

^ Sunda Trench (4°30' S 11°10' S 100°00' E 119°00' Accredited by: SCGN (Apr. 1987) The trench was studied in some detail in 1920s-1930s by Dutch geodesist F.A. Vening Meinesz, who made classic pendulum gravity measurements in a Dutch submarine. Shown as Java Trench in ACUF (Advisory Committee on Undersea Features Gazetteer). see also: http://www.gebco.net/
^ Heather A. Stewart, Alan J. Jamieson: The five deeps: The location and depth of the deepest place in each of the world's oceans. In: Earth-Science Reviews 197, October 2019, 102896, doi:10.1016/j.earscirev.2019.102896.
^ Davis, Katharine. "Asia primed for next big quake". New Scientist.
^ IOC: Towards a Tsunami Warning System in the Indian Ocean Archived 1 February 2006 at archive.today
^ "Press Release: Folded sediment unusual in Sumatran tsunami area". Penn State University. 2 February 2007. Archived from the original on 28 December 2018. Retrieved 3 August 2017.
^ "Presentation of the Drake Medal to Dr Robert L. Fisher" (PDF). National Geophysical Data Center. 30 April 2006. Archived from the original (PDF) on 30 April 2006.
^ "The underwater survey of the SUMATRA earthquake source area". jamstec.go.jp.
^ ^a ^b Hydro International.com (18 June 2019). "Exploring the Deepest Points on Planet Earth". hydro-international.com. Retrieved 20 June 2019.
^ Five Deeps Expedition (16 April 2019). "Deep sea pioneermakes history again as first human to dive to the deepest point in the Indian Ocean, the Java Trench" (PDF). fivedeeps.com. Retrieved 20 June 2019.
^ "Nippon Foundation-GEBCO Seabed 2030 Project". seabed2030.gebco.net. Archived from the original on 16 June 2019. Retrieved 20 June 2019.
^ "Major partnership announced between The Nippon Foundation-GEBCO Seabed 2030 Project and The Five Deeps Expedition". gebco.net. 11 March 2019. Archived from the original on 19 June 2019. Retrieved 19 June 2019.
^ "Home". fivedeeps.com. Retrieved 9 January 2019.
^ Bongiovanni, Cassandra; Stewart, Heather A.; Jamieson, Alan J. (2022). "High‐resolution multibeam sonar bathymetry of the deepest place in each ocean". Geoscience Data Journal. 9. Royal Meteorological Society: 108–123. doi:10.1002/gdj3.122. S2CID 235548940.