When a seismic wave crosses a boundary, it will change directions in the process of

When a seismic wave crosses a boundary, it will change directions in the process of Refraction.

Explanation:

Refraction is the change in direction and speed that a wave will carry when it passes from one medium to another.

When a seismic wave travels through the interior of the Earth, the direction in which it will go is determined by speed.

Refraction has an important role in this process. The deeper the place where the wave moves, the faster it will travel. What refraction does is that the path that the body waves will follow curves upwards.

In this case, refraction is the transition between the earth's mantle and the nucleus.