Editing Challenger Deep (section)

===1976–1977 – RV ''Kana Keoki''===
[[File:Cross section of mariana trench.svg|thumb|upright=1.75|Pacific plate subduction at the Challenger Deep]]
On Leg 3 of the Hawaii Institute of Geophysics' (HIG) expedition 76010303, the {{convert|156|ft|0|adj=on}} research vessel ''Kana Keoki'' departed Guam primarily for a [[seismic]] investigation of the Challenger Deep area, under chief scientist Donald M. Hussong.<ref>{{cite book |chapter-url=ftp://soest.hawaii.edu/dkarl/misc/dave/UH%26theSea/Q-Chapter13.pdf |title=UH and the Sea |first=David |last=Karl |chapter=UH Fleet Assets (1962–2003) |pages=15–21 |access-date=24 November 2019 |archive-date=18 March 2023 |archive-url=https://web.archive.org/web/20230318144755/ftp://soest.hawaii.edu/dkarl/misc/dave/UH%26theSea/Q-Chapter13.pdf |url-status=live }}</ref> The ship was equipped with [[Seismic source|air guns]] (for seismic reflection soundings deep into the [[Earth's mantle]]), [[magnetometer]], [[gravimeter]], 3.5&nbsp;kHz and 12&nbsp;kHz sonar transducers, and precision depth recorders. They ran the Deep from east to west, collecting single beam bathymetry, magnetic and gravity measurements, and employed the air guns along the trench axis, and well into the [[backarc]] and [[forearc]], from 13 to 15 March 1976. Thence they proceeded south to the [[Ontong Java Plateau]]. All three deep basins of the Challenger Deep were covered, but ''Kana Keoki'' recorded a maximum depth of {{convert|7800|m|ft|0|abbr=on}}.<ref>MGD77-398858 {{full citation needed|date=January 2020}}</ref> Seismic information developed from this survey was instrumental in gaining an understanding of the [[subduction]] of the [[Pacific Plate]] under the [[Philippine Sea Plate]].<ref>"International Decade of Ocean Exploration, Progress Report Volume 7, April 1977 to April 1978", US Dept of Commerce, NOAA, Environmental Data and Information Service, October 1978, p. 61</ref> In 1977, ''Kana Keoki'' returned to the Challenger Deep area for wider coverage of the forearc and backarc.