Question

What Is Inside Earth?



Scientists cannot directly study Earth's layers due to their depth and temperature. Instead, scientists use seismic waves to understand the layers within Earth. When an earthquake occurs, seismic waves spread out in all directions through Earth's interior. Seismic stations located at different distances from an earthquake's epicenter, or the location on Earth's surface above the origin of the earthquake, will record seismic waves that scientists will then analyze.



The two main types of seismic waves are P-waves, or primary waves, and S-waves, or secondary waves. P-waves travel faster than S-waves and can travel through liquids and solids, while S-waves can only travel through solids.



The speed and direction of seismic waves depends on many factors. Those factors include composition, mineral phase, packing structure, temperature, and pressure of the media through which the waves pass. All waves change direction when they pass through layers of different density.



The diagram shows how P- and S-waves travel through Earth from an earthquake's epicenter. P-waves are represented by white lines, and S-waves are represented by grey lines.





Why does Earth's core not show S-waves in the diagram?


Earth's outer core is liquid.


Earth's inner core is solid.


Earth's outer core is solid.


Earth's inner core is liquid.

Answer 1

Earth's outer core is liquid.

S-waves cannot travel through liquids, so they are blocked by the liquid outer core and do not appear on the far side of the core in the diagram.