Humans cannot hear sounds with a frequency below about 20 Hz. Sound with a frequency less than 20 Hz is called infrasound. It is a longitudinal wave, just like audible sound, but there are fewer than 20 vibrations every second.
Infrasound is made naturally by earthquakes, volcanic eruptions and thunder. Some large animals, such as elephants and whales, also use it to communicate over long distances, because low frequency sound loses little energy as it travels.
Infrasound has a very long wavelength. Wavelength = wave speed ÷ frequency. In air, sound travels at about 340 m/s, so infrasound of frequency 10 Hz has a wavelength of 340 ÷ 10 = 34 m.