2. 1. What is the difference between compressional (P) waves and shear (S) waves?

3.  Compressional waves move by compressing and expanding the material through which the wave travels. The compression and expansion happen in a direction parallel to the direction in which the wave travels. Move through solid, liquid and gas.

4.  Shear waves move by pulling the material back and forth in a direction perpendicular to the direction in which the wave travels. Move through solids only.

5.  2. How do earthquakes produce seismic waves?

6.  An earthquake produces powerful vibrations in the Earth. These vibrations move out in all directions from the Earthquake as seismic waves.

7.  3. How would you describe wave refraction?

8.  Refraction is the change in direction of a wave that happens when a wave changes speed when it crosses a boundary between two different materials.

9.  4. What is the focus of an earthquake?

10.  The focus on an earthquake is the place in the Earth where the earthquake occurs.

11.  5. How are earthquake waves detected on the surface of the Earth?

12.  Earthquake waves are detected on the surface by recording instruments called seismographs.

13.  6. How do scientists know that the Earth’s mantle is made of solid rock?

14.  Scientists know that the Earth’s mantle is made of solid rock because shear waves can be detected as passing through it. If the mantle were liquid, shear waves would not be able to pass through the mantle.

15.  7. How do scientists know that the Earth has a core?

16.  Scientists know that the Earth has a core because there is a zone, on the other side of the Earth from where an earthquake happens, where no waves are detected. The only way to account for that zone, which is called the shadow zone, is that there is a boundary deep within the Earth where the speed of seismic waves suddenly decreases. The body of material below that boundary is called the core.