1. Earthquakes
And Faults

2. Real- Time Earthquake Data

3. EQs
EQ = Movement of E’s lithosphere that occurs when rocks in the lithosphere suddenly shift, releasing stored energy.
EQs occur b/c stress forces of have exceeded the strength of rock.
Stress builds when rocks along 2 sides of a fault snag and lock (friction) as stress builds – so does POTENTIAL ENERGY IN ROCKS
When rocks are strained beyond limit – they break & move. (Potential  Kinetic Energy in form of seismic waves)

4. Elastic Rebound
Tendency for deformed rock along a fault to spring back to original shape.
Stretched/strained rock store “elastic” or potential energy

5. Stress & Strain on Rocks
Stress – Force that squeezes rocks together, pulls them apart, pushes in diff. directions.
Stress causes strain or deformation (change in shape or volume) of rock
Stress
Folds
Faults
Does not exceed rock strength
Exceeds rock strength

6. Stress Faults = Breaks in rock layers & movement along breaks
Folds = Bending rock layers
Faults = Breaks in rock layers & movement along breaks
Does not exceed rock strength
Exceeds rock strength
High Temps. & Pressure (deeper in crust)
Low Temp. & Pressure – Near Crust

7. Folds
Anticline = up facing fold
Syncline = down ward facing fold

8. Faults

9. Types of Faults 1. Dip – Slip Motion up or down fault surface
Reverse or Thrust: Hanging wall moves UP.
b. Normal: Hanging wall moves DOWN

10. Types of Faults
2. Strike – slip Sliding – Horizontal Movement 3. Oblique – slip dip-slip & strike slip combined

11. Interpretation of Tectonic History
Plate Boundary:
Convergent
Interpretation of Tectonic History
Divergent
Transform
Thrust/Reverse
Normal
Strike-Slip

12. EQ Vibrations EQ vibrations begin at a point called a FOCUS.
Vibrations travel from focus through the earth’s crust as waves.
Surface directly above the focus is called the epicenter.
These waves can be detected and measured on earth’s surface with a SEISMOGRAPH.

13. SEISMOGRAPHS
Instrument that measures & records EQ waves. Strength of EQ waves is referred to as MAGNITUDE.
Wave Motion:

14. 3 Types of Seismic Waves 1. Primary Waves (P waves)
2. Secondary Waves (S waves)
Surface Waves
Each wave originates from the FOCUS of the earthquake.
Each wave travels in a different way, at different speeds, and causes different amounts of destruction.

15. Seismic Waves = vibrations produced by energy released during EQ
P Waves: Primary Wave
Arrives 1st & Travels FASTER.
Compress & Expand like accordion (like sound waves) Push/Pull waves
Move through Solids & Liquids
Least destructive
Virtual EQs
Seismic Waves

16. Seismic Waves S Waves – Secondary What you FEEL in an EQ
Rock moves up & down or side to side (Snake-like)
Arrive after P
Move only through SOLIDS

18. Seismic Waves: Surface Waves
Surface Waves develop when vibrations reach surface
Slowest waves
Most destructive, most damaging
More P & S wave animations:
Video clip:

19. Foreshocks - Small Eqs that may precede major EQ
Aftershocks – Eqs after major EQ (hours/weeks); not all elastic energy is released

20. Rating Earthquakes
Earthquakes are rated in terms of MAGNITUDE or INTENSITY by different scales.
Moment Magnitude Scale
Richter Scale
Mercalli Scale

21. Moment Magnitude Scale
Uses a seismogram
Rates on scale from 1- 10
Looks at Eqs in terms of ENERGY
Each # releases ~32 times more ENERGY than the # before it.
Example
A 6 releases 31 times more energy than a 5, and a 5 releases 31 times more energy than a 4. The energy difference between a 4 and a 6 EQ is 31 X 31 = 961

22. Richter Scale Uses a seismogram Rates on scale from 1- 10
Looks at Eqs in terms of the SIZE OF THE WAVES
Each # has waves 10x bigger than previous #
1 – 3: Small earthquake waves – very little shaking
4 – 6: Moderate earthquakes – noticeable shaking and some damage
BIG Earthquakes – Very destructive

23. Mercali Intensity Scale
Measures observed RESULTS or DAMAGE of Earthquake on a 1 – 12 scale
Degree of shaking and DAMAGE to structures
Don’t need a seismogram
Link

24. Seismic Shaking – ground vibrations caused by seismic waves
Seismic Shaking – ground vibrations caused by seismic waves. Can cause … building collapse, gas/water pipes to burst, fires
Amount of shaking depends on magnitude & type of rock/soil
EQ Hazards
2. Liquefaction - water-logged soil can behave as a liquid when seismic waves interact with; building/bridge collapses

25. EQ Hazards 3. Landslides/ Mudflows – loose soil/rock moves downhill
Tsunamis:; caused by water displacement due to EQ at sea (usu. Subduction);
Starts as a 1m high wave in open ocean; wave grows as it slows and enters shallow coastal waters

26. Seismic Waves are used to Study Earth’s Interior
P and S waves are “bent” and their velocities are affected as they move through material of varying density
Link:

27. Latest Quakes
Top Ten Lists

28. Links Virtual Earthquakes
Wave Types
Triangulation & “Hearing EQs”
More virtual seismograms
Earthquakes outline subducting slab – Interactive Web Lab

31. CH OUTLINE QUIZ
Contrast a focus and an epicenter.
Name 3 types of seismic waves. Provide a description for each.
Name 2 scales that evaluate or measure Eqs. How are these scales different from one another?
What is the relationship b/w Eqs and plate boundaries?