UPSC Prelims 2001 Q59: Geography – Physical Geography & Geomorphology
Consider the following statements regarding earthquakes:
I. The intensity of an earthquake is measured on the Mercalli scale.
II. The magnitude of an earthquake is a measure of energy released.
III. Earthquake magnitudes are based on direct measurements of the amplitude of seismic
waves.
IV. In the Richter scale, each whole number demonstrates a hundred - fold increase in the amount
of energy released.
Which of these statements are correct?
- (a) I, II and III
- (b) II, III and IV
- (c) I and IV
- (d) I and III
Answer: (a) I, II and III
Explanation
Statements regarding earthquakes
| Statement | Verdict |
|---|---|
| I. Intensity is measured on the Mercalli scale | Correct — intensity is based on observed damage and effects |
| II. Magnitude is a measure of energy released | Correct |
| III. Magnitudes are based on direct measurement of seismic wave amplitude | Correct — Richter magnitude comes from the amplitude recorded on seismographs |
| IV. Each whole number on the Richter scale is a hundred-fold increase in energy | Wrong — each step is 10 times the amplitude and about 32 times the energy |
Statements I, II and III are correct. The Richter scale is logarithmic: one whole step means ten times the wave amplitude and about 31.6 times the energy released, not a hundred times.
Answer: (a) I, II and III.
Why each option is right or wrong
- (a) CORRECT. I, II and III are right; IV gets the energy factor wrong.
- (b) Incorrect. Statement IV is wrong and I is left out.
- (c) Incorrect. Statement IV is wrong.
- (d) Incorrect. Statement II is also correct.
Key point
Intensity (Mercalli, I–XII) varies with place; magnitude (Richter, now moment magnitude) is one number per earthquake.
Remember
Mercalli = intensity (effects); Richter = magnitude (energy); one step ≈ 32× energy.
Common mistakes
- Thinking each step is 100 times the energy.
- Mixing up intensity and magnitude of a quake.
- Thinking the Mercalli scale measures energy.
Exam tip
Richter step: ×10 amplitude, ×~32 energy.
Sources
- NCERT Class XI — Fundamentals of Physical Geography, chapter 'Interior of the Earth' (earthquakes)
- United States Geological Survey — Earthquake Magnitude, Energy Release, and Shaking Intensity