Final answer:
Seismic waves produced by earthquakes provide evidence about Earth's interior. P-waves can travel through a liquid and pass through Earth's core, while S-waves cannot. This is why a 'shadow zone' is visible, indicating that the outer core is liquid.
Step-by-step explanation:
Seismic waves produced by earthquakes provide evidence about Earth's interior. P-waves, also known as compression or longitudinal waves, can travel through a liquid and pass through Earth's core.
On the other hand, S-waves or shear or transverse waves cannot travel through a liquid and are not transmitted through Earth's core. This is why we can see a 'shadow zone' indicating that the outer core is liquid.