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UPSC Prelims 2005 · World Geography · Rocks, Quakes and Landforms
Consider the following statements: Which of the statements given above is/are correct?
- The Richter scale is logarithmic and so an increase of 1 magnitude unit represents a factor of 10 times in amplitude.
- Each integer reading of the Richter scale has an energy 100 times that of the previous integer reading.
- (a) 1 only
- (b) 2 only
- (c) Both 1 and 2
- (d) Neither 1 nor 2
Show the answer and explanation
Answer: (a) 1 only
10× amplitude is right; energy rises ~32×, not 100×.
Statement by statement
1. ✓ CORRECT Each whole number on the logarithmic scale means 10 times the wave amplitude.
2. ✗ WRONG Each step releases about 31.6 times more energy, not 100 times.
The idea
A logarithmic scale compares ratios, not equal additions of shaking. Wave amplitude and energy are different quantities and rise at different rates with magnitude. Use the amplitude rule for the first statement and the energy rule for the second.
Why the others are wrong
(b) Accepts 100×.
(c) Accepts 100×.
(d) Rejects the 10× amplitude rule.
The trap
Two steps up = ~1,000× energy — 100× is a common slip.
Elimination technique
The 100-fold figure belongs to amplitude over two magnitude steps, not energy over one step. Reject Statement 2, eliminating (b) and (c); the logarithmic amplitude rule then separates (a) from (d).
Also know
Magnitude describes the earthquake as a source; intensity describes its effects at a particular place. Modified Mercalli intensity uses observed shaking and damage. Moment magnitude is widely used for large earthquakes because it relates to fault area, slip and rock strength. Two places can have different intensities from the same earthquake.
🔒 Richter: +1 = 10× amplitude, ~32× energy.
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