“Infra” or low frequency sound are frequencies below 20 Hz, the threshold of average human hearing. Many animals – mostly large ones – use infrasound to communicate over long distances because it travels further than higher frequencies. For example, blue whales – the largest animal – communicate over hundreds of miles and are the “loudest” animal in the world (“loud” being amplitude or the strength of the signal) – but they do so in the 10-30 Hz range similar to elephants, so we can’t hear them “yelling”.
In regards to localizing (higher frequency) sound, elephants most likely use the same system all animals use, which is that there is a very small time delay between the arrival of the sound to each ear because they are different distances from the source. Some animals like barn owls also have their left/right ear openings offset so that they can triangulate (three dimensions) a sound source, typically a rodent, with near perfect accuracy in total darkness.
But….elephants also use another aspect of low frequency sound to “hear”, which has to do with the tendency of low frequency sound to vibrate solids and liquids (simply look at a large speaker diaphragm or a glass of water when bass notes are played and you’ll see them vibrate). Careful observation by field scientists combined with GPS tracking and directional technology sensitive to low frequency sound indicate elephants can “hear” through their feet, that is, sense low frequency ground vibrations of the “elephant frequency” – elephants do not have hard hooves like horses or buffalo, but large, skin covered pads on the bottom of their feet. It has also been observed that elephants tend to orient their bodies in the direction of their “foot hearing”, which may mean they are using the distance separating their front/back/left right feet like they, and other animals, use their left/right ears to discriminate the directional source of the sound.
I have seen what I believe to have been elephants “listening” to low frequency sounds more than once in Africa: the herd suddenly stopping what they are doing as a group, exactly as if they were listening to something (which I could not hear), but not lifting their trunks or looking in the same direction, or flaring their ears, which would suggest a smell/sight/higher frequency stimulus.
Below, anatomy of an elephant’s foot. Unlike horses or buffalo, elephants have a skin covered pad on the bottom of their foot, under which is a pad of fat and connective tissue that may help to amplify low frequency sound “heard” through their feet.