1. Earthquakes

2. Plate Boundaries
Sketch the 3 type of plate boundaries

3. Pacific-North American Plate Boundary
LA on Pacific Plate
San Francisco on North American Plate
San Andreas Fault is boundary
Relative motion
Takes Big Bend above LA area and causes compression in our area

4. Earthquake Study Seismology – the study of earthquakes (#27)
Seismologist – person who studies earthquakes

5. Where?
Most occur near tectonic plate boundaries

6. Causes
Deformation – bending, tilting, and breaking of Earth’s crust (#28)
Caused by plates pushing, pulling & sliding
2 kinds of deformation
Plastic – bends like piece of soft clay
No earthquake
Elastic – stretches like a rubber band
Earthquake

7. Elastic Rebound
Elastic rebound – sudden return of elastically deformed rock to its undeformed shape
Like a stretched rubber band that breaks and returns to its unstretched shape, now in 2 pieces
Energy released as seismic waves

8. Normal
Divergent
Strike-slip
Transform
Reverse
Convergent

9. Body Waves
Seismic waves – waves of energy that travel through Earth, away from an earthquake in all directions (#29)
Two types of body waves that travel through interior of Earth
P waves
Primary waves (#30)
Pressure waves (#30)
Back and forth motion (#30)
Go through solid, liquid, gas
Fastest wave
S waves
Secondary waves (#31)
Shear waves (#31)
Side to side motion (#31)
Go through solids only
Slower wave, 2nd to arrive

10. More Waves Surface waves – waves that move in top few km of the crust
Up, down, circular motion
Back and forth motion
Travel slower than body waves
More destructive

11. Draw pictures of P and S Waves

12. Measurement
Seismograph – instrument that records ground vibrations to find location and strength of earthquake
Seismogram – tracing of earthquake motion created by a seismograph
Epicenter – point on Earth’s surface directly above an earthquake (#32)
Focus – point on a fault where earthquake motion first occurs (#33)

13. Earthquake Location

14. Finding Epicenter – Step 1
Scientists use the S-P Time Method
Use a time-distance graph
S and P curves are already calculated
Determine distance away from epicenter for at least 3 seismograms

15. Finding Epicenter – Step 2

16. Earthquake Strength Richter Magnitude Scale –
Created in 1930s by Charles Richter
Magnitude measures strength of earthquake by ground motion adjusted for distance from epicenter
Each unit represents 10x increase in strength
5.0 is 10x stronger than a 4.0
6.0 is 100x stronger than a 4.0

17. Richter Magnitude Scale

18. Earthquake Intensity
Intensity – degree to which earthquake is felt and amount of damage caused
Modified Mercalli Intensity Scale
Numerical scale from I to XII
I not felt by people
XII total destruction
Intensity values highest near epicenter

19. Earthquake Hazards
How likely area is to have a damaging quake in the future

20. Earthquake Forecasting

21. Gap Hypothesis
Areas on active faults that haven’t had many earthquakes are likely to be sites for future strong earthquakes.
Known as seismic gaps

22. Earthquake Preparations
Resistant buildings
Mass damper
Active tendon system
Base isolators
Cross braces
Flexible pipes
Retrofitting
Reinforce columns
Fasten to foundation

23. What to do in an Earthquake
Before shaking
Put heavy objects down low
Have an emergency meeting place
Store emergency supplies
During shaking
Crouch or lie under a strong table or desk
Outside – lay down away from buildings, trees, power lines
Stop car and stay inside
After shaking
Stay calm and think
Get away from danger areas
Prepare for aftershocks
Follow emergency plan

24. Earthquake Examples
Normal
Reverse
Strike slip

25. Normal Fault Example Dixie Valley-Fairview Peaks, Nevada earthquake
December 16, 1954

26. Thrust Fault Example

27. Thrust Fault Example

28. Strike-slip Fault Example
Strike-slip example
moletrack

29. Strike-slip Fault Example
Before earthquake manure pile was under window where farmer shoveled it out from inside
Fault runs right under corner of barn
After earthquake manure pile moved over about 10 feet
1906 San Francisco Earthquake

30. Earthquake Effects Ground shaking
Liquefaction – solid earth turns to liquid
Surface faulting
Landslides
Fires
Tsunami

31. Earthquake Effects - Ground Shaking
Loma Prieta, CA 1989
KGO-TV News ABC-7

32. Earthquake Effects - Ground Shaking
Kobe, Japan 1995

33. Earthquake Effects - Liquefaction
Source: National Geophysical Data Center
Niigata, Japan 1964

34. Earthquake Effects - Surface Faulting
Landers, CA 1992

35. Earthquake Effects - Landslides
Source: National Geophysical Data Center
Turnagain Heights, Alaska,1964 (upper left inset);
Santa Cruz Mtns, California , 1989

36. Earthquake Effects - Fires
Loma Prieta, CA 1989
KGO-TV News ABC-7

37. Earthquake Effects - Tsunamis
1957 Aleutian Tsunami
Photograph Credit: Henry Helbush. Source: National Geophysical Data Center