Question

A group of students are studying the waves generated by an earthquake. They observe that the waves on the seismograph point to a location far away from the original earthquake. Which of these most likely causes the waves to point to a far off location?
bending of the waves at the crust
bending of the waves at the outer core
reflection of the waves at the Earth's core
reflection of the waves at the Earth's mantle

Answer 1

Answer: Option (B)

Explanation: The seismic waves namely P and S-waves travels through the interior of the earth, and P-waves propagates faster than S-waves. Both P and S waves undergoes reflection and refraction method.

When P-wave propagates through the mantle, due to its high velocity, it gets bend outward. This waves then reaches the core-mantle boundary, where the P-waves gets refracted inward through the outer core because of the increasing density. P waves can travel both in solid as well as liquid.

It is same in case of S-waves also, but it is comparatively slower than the P-wave, and this wave decreases with the increasing density and gets completely absorbed as they reach the outer core. S waves can travel only in solids.

This seismic waves when recorded on the seismograph during an earthquake, it depicts the changes that happens on the core-mantle boundary. So this data suggests that the waves undergoes bending at the outer core.

Thus, the correct answer is option (B).

Answer 2

reflection of the waves at the Earth's core