This thundering is the actual sound of the Japan 9.0 earthquake, recorded in real time by the deep ocean hydrophone network of the Japan Agency for Marine-Earth Science and Technology in Hatsushima—on March 11, at 14:45 local time.
It was processed by LIDO (Listening to the Deep Ocean Environment), an international ocean sound monitoring program led by the Laboratory of Applied Bioacoustics of the Universitat Politecnica de Catalunya. They accelerated the signal 16 times so it could be audible by human ears. The spectrogram shows the intensity and frequency of the sound. [LIDO]