vibrations with frequencies lower than 20 hertz

Infrasound is a type of sound with a frequency lower than humans can hear. This frequency is lower than 20 hertz. When the frequency is lower but the volume is loud enough, humans can feel the vibrations but cannot hear the infrasound. Younger people have the ability to hear lower and higher frequencies. Some animals including whales and elephants can communicate long distances by infrasound.

Infrasound arrays at infrasound monitoring station in Qaanaaq, Greenland.