How does seismology reveal structures deep inside Earth?

Seismology reveals the Earth's deep structure primarily through the analysis of seismic waves generated by earthquakes or explosions. By measuring the travel times and paths of these waves as they propagate through the planet, scientists can infer the density, composition, and physical state of internal layers.12

The two main types of body waves used for this exploration are:
* P-waves (Primary waves): These longitudinal waves travel through both solid and liquid materials. Their velocity changes as they pass through different layers, allowing researchers to identify boundaries like the Mohorovičić discontinuity and the liquid outer core.32
* S-waves (Secondary waves): These transverse waves travel only through solids. Their observed absence in the Earth's outer core provides compelling evidence that this region is liquid.2

Modern seismological tomography—analogous to medical X-ray imaging—uses high-speed computers to process vast amounts of travel-time data, creating three-dimensional images of internal anomalies. This technique has mapped complex structures, including the lithosphere, subduction zones, and the boundaries of the inner and outer core.14