1. Earthquakes! OBJECTIVES Differentiate between Focus & Epicenter
Movement of the 3 Faults
3 Types of Waves
Differentiate between magnitude & intensity.

2. What causes Earthquakes??
Movement of tectonic plates
Volcanic eruptions
Focus: Origin of the earthquake inside the earth.
Epicenter: Point directly above the earthquake’s focus on the surface of the earth.
Most earthquakes occur when rocks break deep within Earth, caused by stress on the rock.

4. Faults
The resulting fracture where the plates separate is called a fault.
3 Types of Faults
Normal Fault
Reverse Fault
Strike-Slip Fault

5. Normal Fault
Result of plates moving apart.

6. Reverse Fault
Result of plates moving together.

7. Strike-Slip Fault Result of plates sliding past each other.
Ex. San Andreas fault in California

8. Waves
When the fault is formed, it releases built up energy in the form of seismic waves.
Seismic Waves are the vibrations felt on the surface.
3 Types:
P-Waves
S-Waves
Surface Waves

9. P-Waves Primary waves Rocks move back & forth under the surface.
Travel the fastest
Travel through ANY material
Can only travel in the Earth’s interior

10. S-Waves Secondary waves Rocks move up & down under the surface
Will only travel through solids
Can only travel through the Earth’s interior.
Slower than P-waves but faster than surface waves.

11. Surface Waves
Rocks move up & down AND back & forth at the surface. (two directions)
Can only travel on the Earth’s exterior

12. Measurement
Seismometer: Instrument that detects & measures seismic waves
Measures magnitude & Intensity.

13. Magnitude: Amount of energy released during an earthquake.
Intensity: The amount of damage done to the structures involved.
Magnitude does NOT change with distance from the Earthquake. (Energy is energy!!)
Intensity DOES change with distance.
Farther away = Less intensity

14. Richter Scale Measures the magnitude of an Earthquake.
Ranges from 1 (weak)  10 (strong)
Used mainly by the media.

15. Moment Magnitude Scale
Used by seismologists
The best scale
Can be used for ALL quakes – large or small, any distance near or far.

16. Moment Magnitude Scale Illustrated