1. Earthquake Lecture Loma Prieta Earthquake in 1989
Bay Bridge collapse in 2009

2. Earthquakes Result From Stress Inside Earth
What is an Earthquake?
a. Earthquake (Def) - Shaking of Earth’s crust when energy is released. It snaps like a tired, old schoolteacher!

3. Stress and Strain
Earthquake happen when rocks break (fracture). Stress is the forces placed on rocks.
Tensional stress pulls the rocks apart.
Compressional stress pushes them together.
Shear stress twists and contorts rocks in opposite motions.

4. Types of Earthquake Faults
There are three basic types of faults
1. Reverse Faults
2. Normal Faults
3. Strike-slip Faults

5. Normal Faults
Normal Faults form as a results of horizontal tensional forces
The crust is extended and pulled.
Footwall is higher
Example: Lake Tahoe formed through normal faulting
Often occur at divergent boundaries

6. Reverse Faults (also known as Thrust Faults)
Form as a result of compressional forces
The hanging wall is higher
Often occur at convergent boundaries

7. Example of a reverse Faults – One rock layer pushed over another rock layer (high angle).
Reverse faults are steep!

8. Strike-Slip Fault
Strike Slip are formed as a result of shearing forces
Movement along strike slip faults are mostly horizontal
San Andreas Fault
Often occur at Transform boundaries

9. Earthquake Focus and Epicenter
The Focus is the point where the earthquake originates!
The focus is always beneath the Earth’s surface.
Earthquakes can be shallow or deep.
The epicenter is on the Earth’s surface directly above the focus

10. Deep and Shallow Earthquakes
Deep earthquakes occur in subduction zones
Trenches are deeper than Mt. Everest is high!

11. Seismic Waves
P-Waves – Primary waves. Remember particles move parallel to direction of wave motion. Compression & rarefactions!
2) S- Waves - Secondary (shear) waves don’t travel through liquids! Particle motion is perpendicular to wave direction of travel. Transverse waves.
3) Surface Waves (also called L-waves)– Circular waves travel along Earth surface. Destroys buildings.

12. Clues to Earth’s Interior using Seismic Waves
S-waves travel through solids only so when they hit the liquid core, they are deflected. Shows us the outer core is liquid.
P waves speed up when they hit the inner core which supports the idea that the inner core is solid

13. Locating and Measuring Earthquakes
1.Seismographs – Recording instruments.
a. Seismogram – Sheets of paper quakes are recorded on.
2. Distance to the Epicenter – Receiver stations around the world help us triangulate & find epicenters.

14. Travel-Time Graphs and Locating Epicenters
The epicenter can be determined with the seismic data from three stations.
Data from one station gives distance from the epicenter but not exact location.

15. Measuring Earthquakes
Magnitude – Size of earthquakes
Richter Scale – Logarithmic scale of energy released.
Scale of 1-10 (though 10 has never happened)
Damage
Mercalli Scale – Based on observers’ assessment of the Earthquake damage (I-XII)

16. Some Famous Earthquakes
To see the biggest quake in 100 years, go here:

17. Tsunamis – Giant water waves generated by earthquake energy.
Photo taken seconds before this man got swept away!

18. Tsunamis – Giant water waves
Tsunamis – Giant water waves. This picture was taken from a hotel room right before the tsunami hit in Indonesia.