The deep interior of the Earth is studied using which method?

• A. Seismic tomography
• B. Seismic waves
• C. Gravity measurements
• D. Seafloor mapping

Answer: (B)

Seismic waves are the primary way we probe Earth’s deep interior. When earthquakes occur, the generated waves travel through the planet and are detected by seismometers around the world. The speeds and paths of these waves depend on the materials they pass through, so by analyzing how long waves take to arrive, how they bend or reflect at boundaries, and the differences between wave types (like P-waves and S-waves), we can map where boundaries lie and whether regions are solid or liquid. For example, S-waves cannot travel through liquid, which creates shadow zones that reveal a liquid outer core, while P-waves refract at core–mantle boundaries, giving clues about depth and composition. Seismic tomography goes a step further by using many wave paths to construct 3D images of interior properties, all rooted in measurements of seismic waves. Gravity measurements and seafloor mapping provide other information but don’t directly reveal deep interior structure in the same way seismic data do.