Sound was sped sped up 16 times. Text in the video explains that the first roar of noise is “earthquake sounds propagating through the earth’s crust” (per the web page, from a hydrophone located in the central north Pacific); the second roar of noise is “earthquake sounds propagating through the ocean” (from a hydrophone located near the Aleutian Islands in Alaska).
For more detailed info, see the VENT Program’s web page about the recordings.
It’s a roar, & then another roar. But impossible to listen to — at least for me — without seeing in my mind’s eye the devastation wrought by the event that produced those roars.
A prayer for the people of Japan. A good time too, if you have the ability, to send some money their way via whatever aid agencies you feel will do the most good.