1. Earthquakes: Forces Inside of Earth

2. Earthquake Causes Fault Formation
Rocks can bend and stretch up to a point – just like a rubber band or popsicle stick
Rocks have a certain amount of elasticity.
Once the elastic limit is passed, rocks may break.
When rocks break, they move along surfaces called faults.
They can move up, down, or sideways

3. What Causes Faults?
The surface of Earth is in constant motion because of forces inside of Earth.
These forces cause the tectonic plates to move.
This movement puts stress on the rocks near the plates edges.
To relieve the stress, the rocks bend, compress, stretch.
If the force is too great, the rocks will break.

4. What is an Earthquake?
When the rocks break from the stress, it produces vibrations.
These are earthquakes.

5. World Earthquakes

6. Recent Earthquakes

7. How Earthquakes Occur
As rocks move past each other, their rough surfaces catch on each other, briefly halting movement along the fault.
However, the forces inside Earth keep driving the rocks to move.
More stress is built up – causing the rocks to break and move.
Earthquakes can be so small that they are unnoticeable or they can be devastating.

8. Types of Faults Three types of forces act on rocks
Tension – pulls rocks apart
Compression – squeezes rocks together
Shear – rocks slide past each other
Three types of faults
Normal Faults
Reverse Faults
Strike-Slip Faults

9. Normal Faults
Tensional forces inside Earth cause rocks to be pulled apart and stretched.
This causes a normal fault.
In a normal fault, the rock above the fault surface moves downward in relation to rock below the fault surface.

10. Normal Fault

11. Reverse Faults
Occur from compression forces that squeeze rock together.
If rock breaks from forces pushing from opposite directions, rock above a reverse fault surface is forced up and over the rock below the fault surface.

12. Reverse Fault

13. Strike-Slip Faults
Occur when rocks on either side of the fault are moving past each other without much upward or downward movement.
San Andreas Fault in California is a Strike-Slip Fault.
This fault is the boundary between two of Earth’s plates that are moving sideways past each other.

14. Strike-Slip Fault

15. San Andreas Fault