UPSC Prelims 2006 Q87: Geography – Physical Geography & Geomorphology
Consider the following statements :
1. The Richter scale is a logarithmic scale and so an increase of 1 magnitude unit represents a
factor of 10 times in amplitude.
2. Each integer reading of the Richter scale has an energy 100 times that of the previous integer
reading.
Which of the statements given above is/are correct?
- (a) 1 only
- (b) 2 only
- (c) Both 1 and 2
- (d) Neither 1 nor 2
Answer: (a) 1 only
Explanation
The Richter scale
| Statement | Verdict | Reason |
|---|---|---|
| 1. Logarithmic scale; one magnitude unit means a factor of 10 in amplitude | True | Each step increases the recorded wave amplitude ten times |
| 2. Each integer reading has 100 times the energy of the previous one | False | Energy rises by a factor of about 31.6, not 100 |
Only statement 1 is correct.
Answer: (a) 1 only.
Why each option is right or wrong
- (a) CORRECT. The Richter scale is logarithmic with a tenfold amplitude rise per unit.
- (b) Incorrect. Statement 2 is false since energy rises about 31.6 times per unit.
- (c) Incorrect. Statement 2 is false, so both cannot be correct.
- (d) Incorrect. Statement 1 is true, so it is not 'neither'.
Key point
One Richter unit is a tenfold increase in amplitude and about 31.6 times more energy, not 100 times.
Remember
Richter scale: 10 times amplitude, about 31.6 times energy per unit.
Common mistakes
- Confusing the tenfold amplitude rise with the energy increase.
- Remembering energy rise as 100 rather than about 31.6.
- Treating the Richter scale as linear rather than logarithmic.
Exam tip
Richter: amplitude x10 per unit, energy about x31.6 per unit.
Sources
- NCERT Class XI Geography — Fundamentals of Physical Geography — Interior of the Earth (earthquakes and the Richter scale)
- United States Geological Survey — Earthquake Magnitude, Energy Release, and Shaking Intensity