Sunda Trench
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 resemblance to suspension bridge cables, with peaks and sags, indicative of asperity and locked faults, instead of the traditional wedge shape expected. Some of the earliest exploration of the Trench occurred in the late 1950s when Robert Fisher, 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. Various agencies have explored the trench in the aftermath of the 2004 earthquake, and these explorations have revealed extensive changes in the ocean floor. On 5 April 2019 Victor Vescovo made the first crewed descent to the deepest point of the trench in the Deep-Submergence Vehicle "DSV Limiting Factor" (a Triton 36000/2 model submersible) and measured a depth of ± by direct CTD pressure measurements at 11°7'44" S, 114°56'30" E, about 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 will be donated to the GEBCO Seabed 2030 initiative. 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. 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 ± at 33°37'52" S, 101°21'14" E for the Dordrecht Deep. This confirmed that the Sunda Trench was indeed deeper than the Diamantina Fracture Zone. 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.
Exploration
Its maximum depth is the deepest point in the Indian Ocean.