Consider the following statements regarding the earthquakes : I. The intensity of earthquake is measured on 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 hundredfold increase in the amount of energy released. Which of these statements are correct ?

Statements I, II and III are correct. The Mercalli (Modified Mercalli) scale measures earthquake intensity by observed effects and damage at locations, i.e., intensity, not energy [1]. Magnitude denotes the size of an earthquake as a measure of energy released and is given as a numeric magnitude (Richter/moment magnitude) [2]. Magnitudes such as the Richter (local) magnitude are based on direct instrumental measurements of seismic-wave amplitudes recorded by seismographs [2]. Statement IV is incorrect: a one-unit increase on the Richter-type scales corresponds to a tenfold increase in measured amplitude but about a 32-fold increase in energy released, not a hundredfold change [3].

Sources

1. [1] FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 3: Interior of the Earth > Measuring Earthquakes > p. 21
2. [2] Environment and Ecology, Majid Hussain (Access publishing 3rd ed.) > Chapter 8: Natural Hazards and Disaster Management > Magnitude of Earthquake > p. 16
3. [3] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 14: Earthquakes > 14.5. Richter Magnitude Scale > p. 182