Question

Which one of the magnitude scales given below DOES NOT saturate while estimating size of carthquakes?

• A. Local magnitude scale (ML)
• B. Body wave magnitude scale (M)
• C. Surface wave magnitude scale (Ms)
• D. Moment magnitude scale (M)

Answer 1

The Correct Option is D

To answer the question regarding which magnitude scale does not saturate while estimating the size of earthquakes, we need to understand the characteristics of different earthquake magnitude scales.

Let us examine each of the given options:

1. Local magnitude scale (ML): This scale, also known as the Richter scale, is commonly used for measuring small to moderate-sized earthquakes. However, it tends to saturate for large earthquakes, typically those over magnitude 6.5 to 7.0. Saturation occurs because the scale was initially designed for seismic waves detectable with short-period seismographs, limiting its capacity to measure larger events accurately.
2. Body wave magnitude scale (Mb): This scale is used to measure the amplitude of P-waves. Like the local magnitude scale, it also saturates and becomes less effective for earthquakes larger than magnitude 6.5 to 7.5.
3. Surface wave magnitude scale (Ms): The surface wave magnitude measures the size of shallow earthquakes using surface waves. It can measure larger events than the local and body wave scales but also saturates for very large earthquakes, usually around magnitude 8.
4. Moment magnitude scale (Mw): This is the modern standard for measuring earthquake size. The moment magnitude scale is derived from the seismic moment of the earthquake, which is a function of the fault slip, the area of the fault that slipped, and the strength of the rocks that faulted. Unlike the other scales (ML, Mb, Ms), the moment magnitude scale does not saturate, making it the most reliable scale for measuring very large earthquakes accurately.

Thus, the moment magnitude scale (Mw) is the correct answer because it does not suffer from saturation when estimating the size of earthquakes. It provides a more comprehensive and detailed measurement, making it suitable for both small and large earthquake events.

Therefore, the correct option is:

• Moment magnitude scale (M)