Question

The earthquake magnitude is the measure of:

• A. Seismic wave amplitude
• B. Seismic wave velocity
• C. Seismic wave length
• D. Seismic wave period

Hint:

Magnitude measures seismic wave amplitude; higher amplitude means more energy released.

Answer 1

The Correct Option is A

To determine what earthquake magnitude measures, let's analyze the given options:

1. Seismic wave amplitude:
Earthquake magnitude is primarily based on measuring the amplitude of seismic waves recorded by seismographs. The Richter scale, for instance, uses the logarithm of the largest seismic wave amplitude to calculate magnitude.

2. Seismic wave velocity:
While wave velocity affects how quickly seismic energy travels through Earth's layers, it is not used to determine earthquake magnitude.

3. Seismic wave length:
The wavelength of seismic waves varies depending on the type of wave (P, S, or surface waves), but it is not a direct factor in magnitude calculations.

4. Seismic wave period:
The period (time between wave peaks) is sometimes considered in modern magnitude scales (like the moment magnitude scale) but is secondary to amplitude in determining magnitude.

Key Point:
Magnitude fundamentally measures the size/energy of an earthquake, which is derived from seismic wave amplitudes adjusted for distance from the epicenter.

Final Answer:
Earthquake magnitude is the measure of seismic wave amplitude.