Which of the following statements is/are correct ? 1. Hypocenter is

Which of the following statements is/are correct ?

  • 1. Hypocenter is the point on the surface of the Earth, nearest to the focus.
  • 2. Velocity of earthquake waves is higher in denser materials.
  • 3. P waves move faster and are the first to arrive at the surface of the Earth.

Select the correct answer using the code given below :

1 and 2
2 and 3
1 and 3
3 only
This question was previously asked in
UPSC NDA-1 – 2023
The correct option is B.
Statement 1 is incorrect because the hypocenter is the point of origin of the earthquake *within* the Earth, while the epicenter is the point *on the surface* directly above the hypocenter. Statement 2 is generally correct as seismic wave velocity increases with the rigidity and density of the medium. Statement 3 is correct; P waves (primary or compressional waves) are faster than S waves (secondary or shear waves) and arrive first.
1. Hypocenter (or focus) is the point below the Earth’s surface where the earthquake originates. The epicenter is the point on the Earth’s surface directly above the hypocenter.
2. Seismic wave speeds depend on the elastic properties and density of the material. Wave speed is proportional to the square root of the ratio of an elastic modulus (like bulk modulus or shear modulus) to density. While density increases with depth, the elastic moduli generally increase faster, leading to an overall increase in wave speed with depth in the Earth’s mantle and core.
3. P waves are longitudinal waves that can travel through solids, liquids, and gases. S waves are transverse waves that can only travel through solids. Because P waves involve compression and expansion, they travel faster than S waves, which involve shearing motion.