pptx on earthquakes

1. Earthquake Basics
Robert Butler
ANGLE Project
https://serc.carleton.edu/ANGLE

2. Stick-slip: Elastic Rebound Theory
Jerky motions on faults produce EQs
Three Fs of earthquakes: forces, faults, and friction.
Slow accumulation and rapid release of elastic energy.
Earthquake Machine

3. Three Basic Types of Plate Boundaries
Transform (e.g. San Andreas Fault)
Strike-slip faulting
Magnitudes generally < 7

4. Three Basic Types of Plate Boundaries
Divergent (e.g. spreading ocean ridge)
Normal faulting Magnitudes < 6

5. Three Basic Types of Plate Boundaries
Convergent (e.g. subduction zone)
Magnitudes up to 9 or larger
Depths to 700 km

6. Hypocenter or Focus: Point WITHIN
Earth where EQ occurred.
Epicenter: Location on Earth’s
surface directly ABOVE the EQ.

7. Body waves
(P and S) travel
inside Earth.
Surface waves
travel along
Earth’s surface.
Body Waves and Surface Waves
While P- and S- waves radiate outward in all directions, surface waves travel
along the surface of the earth and decrease in amplitude with depth.

8. P Waves Are Pressure Waves
P waves are fastest seismic waves.

9. S Waves Are Shear Waves
S waves are slower than P waves
but faster than surface waves.

10. Amplitude greatest at surface,
decreasing with depth.
Slower than P or S waves.
Often are largest amplitude and
most damaging seismic waves.
Surface Waves

11. Human Waves
Modeling P, S, and Surface Waves
Seismic Slinky
Human Waves

12. A seismograph detects
and records earthquakes.
A seismogram is the
earthquake record.
How do scientists detect earthquakes?
When an earthquake occurs the seismic waves travel through the Earth to the
seismic station where the information is transmitted to distant computers.

13. University of Portland AS-1 Seismometer
M7.7 Earthquake off Northern Chile Nov 14, 2007
P waves
~12 min
~720 sec
S waves
~22 min
~1320 sec
Surface waves
~42 min
~2500 sec

14. Seismic Waves from Chile Earthquake
USArray
Animations
QuickTime
Animation

15. Seismic waves crossing the
US recorded by the USArray.

16. Seismic waves crossing the
US recorded by the USArray.

17. Distance of earthquake from seismometer?
Determined from S arrival time - P arrival time.
4 min 45 sec
3300 km

18. Locating an Earthquake
1) Determine distance of EQ from
three seismic stations by
calculating the S minus P arrival
times.
2) Plot them on the travel-time
graph.
3) Intersection of the circles gives
the location.
1
23

19. Moment Magnitude Pasta Quake
QuickTime Animation

20. Magnitudes and Energies of Earthquakes
MOST of the energy is released by ~20 magnitude-7
and larger earthquakes every year.

21. Earthquake Intensity
Violence and Effects of Ground Shaking.
QuickTime Animation

22. Effects of Near-Surface Geology
Amplitude of oscillation increasing

23. Ground-Shaking Amplification
Seismic waves are amplified as they pass from
bedrock into basins filled with sedimentary rock.

24. Liquefaction
What happens to a structure built on a weak
foundation when an earthquake strikes?
Liquefaction
Niigata, Japan, June 16, 1964

25. Duration of Ground Shaking
• Long duration can drive oscillation of large structures.
• Long (bridges) and tall (high-rise) buildings vulnerable.
• Long duration can cause fatigue of welds and bolts.
Why does this matter?
M9.0 Japan 2011 shaking lasted 6 minutes!
Magnitude Duration of Shaking
5.0 – 5.9
6.0 – 6.9
7.0 – 7.9
8.0 – 8.9
9.0 – 9.5
2 – 15 seconds
10 – 30 seconds
20 – 50 seconds
30 – 90 seconds
1.5 – 6.0 minutes
“moderate”
“strong”
“major”
“great”
“great”

26. Seismic Landslides in Anchorage, 1964
Government Hill Elementary SchoolFourth Avenue near C Street

27. Seismic Landslides in Anchorage, 1964
Block diagram of translational landslide.

28. Seismic Landslide Hazard Map
Earthquake Hazard Maps

29. “Earthquakes don’t kill people ……. buildings that
collapse during earthquake ground shaking kill people.”
Build a Better Wall

30. Cripple wall failure
Cripple
Wall
Failure
A common problem
for older wood-
frame houses.

31. Nonstructural Damage
Objects falling are common ”nonstructural” risks.
Many are very easy to secure.

32. Nonstructural Damage
Wood stoves
Fuel tanks
Fire is very common result of ground shaking.

33. Building Resonance
Oscillating blocks experiment
BOSS Model

34. Great Alaska ShakeOut 10:18 AM October 18, 2018