Articles, including the New York Times of 23 November 2017 point to the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) as doing much of the detection and analytical work pointing to an explosion or implosion of ARA San Juan on 15 November 2017.
But note that the US Navy’s own analysts came to the explosion or implosion conclusion by 21 November 2017 "Tuesday night" when the US Navy shared the conclusions with Argentina - 2 days before CTBTO shared their conclusions with Argentina, on 23 November "Thursday night".
CTBTO's hydrophones on 15 November 2017 may have detected San Juan's explosion/implosion where the blue lines cross. However these CTBTO detection points are very distant from San Juan, hence likely requiring closer US Navy hydrophones for mathematical confirmation.
It is likely the US Navy's little advertised unit had more sensitive hydrophones closer to the South American continent – that is closer to San Juan. Hydrophones of other governments (see map below) may have concurred.
An explosion capable of destroying San Juan could have been caused by a buildup of hydrogen gas generated by malfunctions in San Juan's hundreds of tons of batteries. Another explosive cause may have been ignition of torpedo fuel that can almost simultaneously “cook off” one or more of San Juan's 22 torpedo warheads. Perhaps the only "comfort" for relatives was that San Juan's end likely occurred quickly.
An explosion like sound can be an implosion of San Juan once it moves deeper than the approximately 550 metre “crush depth”. San Juan’s main sailing area may have been only 250 metres deep but some parts are 3,000 metres deep.
"Eternal Father, Strong to Save" The Navy Hymn for Submariners