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UPSC Prelims 2001 · World Geography · Rocks, Quakes and Landforms
Consider the following statements regarding the earthquakes: Which of these statements is correct?
- The intensity of an earthquake is measured on Mercalli Scale
- The magnitude of an earthquake is a measure of energy release
- Earthquake magnitudes are based on direct measurements of the amplitude of seismic waves
- In the Richter Scale, each whole number demonstrates a hundred-fold increase in the amount of energy released
- (a) 1, 2 and 3
- (b) 2, 3 and 4
- (c) 1 and 4
- (d) 1 and 3
Show the answer and explanation
Answer: (a) 1, 2 and 3
Mercalli intensity, magnitude as energy, and amplitude-based magnitude.
Statement by statement
1. ✓ CORRECT Intensity (damage felt) is measured on the Mercalli scale.
2. ✓ CORRECT Magnitude measures energy released.
3. ✓ CORRECT Magnitude is calculated from recorded wave amplitudes.
4. ✗ WRONG Each whole number means ~32× more energy, not 100×.
The idea
Magnitude measures the size of an earthquake source, while intensity records how it is experienced at a place. Magnitude scales use instrument-based measurements; intensity uses observed effects. A large change in energy should not be confused with the amplitude ratio on a logarithmic scale.
Why the others are wrong
(b) Accepts 100×.
(c) Accepts 100×.
(d) Drops magnitude as energy.
The trap
100-fold again — it is ~32-fold.
Elimination technique
Reject the 100-fold energy claim in Statement 4. This removes (b) and (c); then keep the valid magnitude-as-energy-size statement to distinguish (a) from (d).
Also know
Distance, depth, local soil and building strength affect damage. Soft sediments can amplify shaking and waterlogged loose sands can lose strength through liquefaction. Modern moment magnitude uses the seismic moment of fault movement; the amplitude statement here reflects the Richter-scale context. Magnitude is not a prediction of identical damage everywhere.
🔒 Mercalli (I–XII) = intensity; Richter / moment magnitude = energy.
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