The deepwater sound channel conducts low frequency noise very efficiently, like a waveguide. The low frequency active sonar which the navy uses is as loud as a 747 jet engine and it can travel a very long distance through the deepwater sound channel without losing much energy. Mass beachings are still common near wherever the navy is testing it's active sonar and beached whales have been found with ruptured inner ears, though I can't find the reports now.

A lot of the navy's active sonar technology is classified so most of what we civilians know about it is based off of hydrophone measurements, autopsies of dead whales, maps of mass beaching events and whatever information the navy has made publicly available.