Earthquake refers to the vibration on the earth's surface caused by catastrophic endogenetic forces.
(A) The magnitude or intensity of energy released by an earthquake is not measured by the modified Mercalli Intensity Scale.
(B) The place on the ground surface which is perpendicular to the focus is called the epicenter.
(C) Seismology is the special branch of geology that deals with the study of earthquakes.
(D) Shadow zones are some specific areas where earthquake waves do not occur or occur rarely.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → (B), (C) and (D) only
An earthquake is measured in two different ways: its magnitude, the energy released, on the Richter scale, and its intensity, the strength of the shaking judged from the damage it causes, on the Mercalli scale.
(A) The magnitude or intensity of energy released by an earthquake is not measured by the modified Mercalli Intensity Scale. Incorrect. The Modified Mercalli Intensity Scale is the very scale used for the intensity of an earthquake: it grades the shaking from I to XII by its effects on people, buildings and the ground. So intensity is measured by it.
(B) The place on the ground surface which is perpendicular to the focus is called the epicenter. Correct. The focus is the point inside the earth where the energy is released; the point on the surface vertically above the focus is the epicentre, where the waves reach the surface first.
(C) Seismology is the special branch of geology that deals with the study of earthquakes. Correct. Seismology studies earthquakes and the seismic waves they send through the earth; the waves are recorded on a seismograph.
(D) Shadow zones are some specific areas where earthquake waves do not occur or occur rarely. Correct. Between about 105° and 145° from the epicentre no direct waves are recorded; S-waves are not recorded anywhere beyond 105°, because they cannot pass through the liquid outer core.
Note: Statement (A) can be read in two ways:
As a statement about intensity — the Mercalli scale does measure the intensity of an earthquake, so (A) is incorrect and Option (4) is the answer, as NTA marks it.
As a statement about the energy released — the energy (the magnitude) is measured on the Richter scale, not on the Mercalli scale, so (A) would be correct; then all four statements are correct, and no option offers all four, so only the first reading fits the options.