Question

what are infrasonic vibration ? what is their ranze in hertz ?

Answer 1

infrasonoc vibrations is that which is  below the frequencies of audible sound, and normally includes anything under 20 Hz.

Answer 2

1.Infrasound, sometimes referred to as low-frequency sound, is sound that is lower in frequency than 20 Hz or cycles per second, the "normal" limit of human hearing.

2.The human range is commonly given as 20 to 20,000 Hz, although there is considerable variation between individuals, especially at high frequencies, and a gradual loss of sensitivity to higher frequencies with age is considered normal.