(1) What is Infrasound?
Infrasound is sound that is lower in frequency than 20 Hz, the normal minimum limit of human hearing.
Hearing becomes gradually less sensitive as frequency decreases, so for humans to perceive infrasound, the sound pressure must be sufficiently high.
The study of such sound waves is sometimes referred to as infrasonics, covering sounds beneath 20 Hz down to 0.001 Hz.
This frequency range is utilized for monitoring earthquakes, charting rock and petroleum formations below the earth,
and also in the study of the mechanics of the heart.
But do you know that animals can use infrasound to communicate?
Infrasound is characterized by an ability to cover long distances and get around obstacles with little dissipation.
(2) Sources of Infrasound
Infrasound sometimes results naturally from severe weather, earthquakes, volcanoes, waterfalls,
lightning etc.
Infrasound can also be generated by man-made processes such as sonic booms and explosions
etc.
(3) Animals and Infrasound
Whales, elephants, hippos, rhinoceros, giraffes, alligators etc are known to use infrasound to
communicate over distances.
For the case of whales, it can be up to hundred of miles.
Migrating birds use naturally generated infrasound, from sources such as turbulent airflow over
mountain ranges, as a navigational aid.
Elephants, in particular, produce infrasound waves that travel through solid ground and are sensed
by other herds using their feet, althought they may be separated by hundred of kilometres.