Question

Some animals get disturbed and start running here and there just before the earthquakes occur because they can hear:

• A. Audible sound
• B. Ultrasonic sound
• C. None of the above
• D. Infrasonic sound

Answer 1

The correct option is D Infrasonic sound

Earthquakes produce an infrasonic sound before the main shock wave. Infrasonic sound is a low-frequency sound. It is a sound that is lower in frequency than $20Hz$ (hertz) or cycles per second, i.e.,the normal limit of human hearing. Hearing becomes gradually less sensitive as the frequency decreases. Thus,for humans to perceive infrasonic sound, the sound pressure must be sufficiently high.
Rhinos have extremely good ears. They pick up infrasonic sound far deeper than the range of human hearing.
Rhinos can hear down to a frequency of $4Hz$, whereas even a human baby, with entirely undamaged ears, can normally only pick up sounds as low as $20Hz$. Giraffes and elephants can also hear in this range.
Hence, we can see that some animals get disturbed and start running here and there just before the earthquakes because they can hear infrasonic sound.