1. What is an earthquake?
An earthquake is the shaking of the ground due to the movements of tectonic plates
Earthquakes occur at different plate boundaries

2. What happens during an earthquake?
Foreshock: any of the usually minor tremors commonly preceding the principal shock of an earthquake
Earthquake!
Aftershock: smaller earthquakes which are generated by the continued movement of plates and other materials after the main shock

3. Parts of an Earthquake
1. The focus of an earthquake is the point WITHIN the Earth where the earthquake starts. It is the place below the earth’s surface where the rocks tear, come apart, or collide.
2. The epicenter is the location on the EARTH’S SURFACE directly above the focus. Surface waves move outward from the epicenter.

4. 3. The fault is the break in the
crust where the earthquake occurs,
between two blocks of rock that
have moved past each other.

5. Types of Faults Strike-Slip, Reverse, Normal
Each fault occurs at a different type of boundary!

6. What is a reverse fault? Convergent Boundary = Reverse
Occur at convergent boundaries, where two plates are colliding
A reverse fault happens when two blocks of crust are pushed up against each other and they slide vertically
These types of earthquakes are usually strong and deep

7. What is a Normal Fault? Divergent = Normal
Occur at divergent boundaries, where plates move away from each other
A normal fault occurs when two blocks of crust are pulled away from each other and slide vertically
This type of earthquake is usually weak and shallow

8. What is a strike-slip fault? Transform = Strike-Slip
If two plates have a transform motion, they will probably have a strike-slip fault between them
A strike-slip fault is when two blocks of crust slide past each other horizontally
These types of earthquakes are moderate and shallow

9. What Causes Earthquakes?
As tectonic plates push, pull or scrape against each other, stress builds up along faults until the rocks finally move
The elastic rebound theory is the main cause of earthquakes

10. Elastic Rebound Theory
Definition: the gradual buildup, and release of stress and strain, between tectonic plates which leads to earthquakes

11. Just the Basics!
What do scientists use to measure the strength of an earthquake?
Magnitude
What do scientists use to measure ground motion?
Seismogram

12. P WAVES
P waves (primary waves) are compression waves. They push (compress) and pull (expand) in the direction that the wave is traveling.
These move really fast! They arrive first, but cause the least damage.

13. S WAVES
S waves (secondary waves) move in right angles and are slower than P waves. They arrive second (hence the name), and cause a moderate amount of damage.

14. SURFACE WAVES
Travel along the earth’s surface. They do not travel through the Earth. They move up and down, or side to side.
Although it is the slowest, this is the most destructive type of wave!