Question

An earthquake produces which kind of sound before the main shock wave begins?
A. Ultrasound
B. Infrasound
C. Audible Sound
D. None of the above

Answer 1

Hint: Waves are the propagation of disturbances in an organized and regular way from place to place. The disturbance oscillates periodically with wavelength and fixed frequency in the simplest waves.

Complete answer:
The sudden movement of the tectonic plates of the earth is why Earthquakes occur, this sudden movement causes tremors in the earth's crust, and thus before the mainshock wave begins, it produces infrasound. There is a sudden release of seismic waves during this process, and it makes the ground shake and these seismic waves are grouped as infrasound waves.
The sound sometimes referred to as a pressure wave, is actually a kind of wave. Humans can hear the sound waves that the ears can collect and transmit to the brain for interpretation. The sound waves of just the correct frequency and size fit into the human ear canal. The hearing range in which humans can hear sound is in the mid-frequency range. Sounds that are in the lower frequency range are known as infrasound, while those sounds that are in the higher frequency range are called ultrasound.

Thus, option (B) is correct.

Note: The number of cycles that occur during a specified period of time is called frequency. The cycle for sound waves is one wavelength, and one second is the time period; the fewer wavelengths in the sound wave per second, the lower the frequency. The sound wave’s frequency is measured in hertz and it is the number of wavelengths measured in one second or per second. Any sound wave having a frequency of 20 Hz or less is generally considered to be an infrasound wave.