Correct Option
The correct option is (c).
Explanation
Earthquake magnitude is a quantitative measure of the energy released at the source of an earthquake. It is measured on the Richter scale, which is logarithmic. Seismographs are the instruments used to detect and record these seismic waves.
Statement-wise Analysis
- Statement 1 is Correct: Earthquakes with a magnitude higher than 7.0 on the Richter scale are classified as "Major" earthquakes. These events release massive amounts of energy and are usually responsible for widespread destruction of life and property.
- Statement 2 is Incorrect: The Bhuj earthquake (2001) and the Kashmir earthquake (2005) were catastrophic events with magnitudes of approximately 7.7 and 7.6 respectively. Earthquakes with magnitudes less than 4.0 are considered minor and typically do not cause structural damage.
- Statement 3 is Correct: A seismograph is highly sensitive and records ground motion caused by seismic waves. An earthquake of magnitude 3.0 is classified as "Minor"; while it may be felt slightly by people indoors, it is distinctly recorded by seismographs.
Key Takeaway
The Richter scale classifies earthquakes based on magnitude: values above 7.0 indicate destructive earthquakes, while values below 3.5 are generally recorded but rarely felt or damaging.