1. College of Central Florida KT Kim
Earthquakes and the Earth's Interior an investigation using human subjects
College of Central Florida
KT Kim

2. Earthquake
Seismology – study of earthquakes and Earth’s interior using seismic waves

3. Earthquake Stress (Force) causes rock to deform
Three types of deformation
Elastic deformation (Vibration, wave propagation)
Plastic deformation (Folds)
Fracturing (Faults)

4. Earthquake
Earthquake – sudden motion or trembling caused by the abrupt release of energy
Slippage: minor movement (aseismic, fault creep)
Fracture: larger movement (seismic)

5. Earthquake Waves propagate through medium
Focus – rupture point where energy is released
Epicenter – point on Earth’s surface above the focus

6. Seismic Waves Body waves – travel through Earth’s interior
P wave – compressional elastic wave
pressure wave, primary wave
S wave – shear wave, secondary wave
Surface waves – travel through Earth’s surface
Rayleigh waves – rolling (retrogressive) waves
Love waves – Side-to-side waves

7. Seismic Waves Measuring seismic waves
Seismograph – the instrument
Seismogram – the record it makes
Measurement of earthquake strength
Mercalli scale – measures damage
Richter scale – measures energy
Moment-magnitude – measures energy as a function of movement and fault surface area

8. Richter Earthquake Magnitude
Measure S-P time
(25 seconds)
Measure the largest amplitude (20 mm)
Plot them on the corresponding axes.
Connect a line.
Read a magnitude (5)

9. Example 1
If we compare two earthquakes; one (A) has a magnitude of 5 and the other (B) has a magnitude of 6. What is an amplitude ratio?
Magnitude difference = 6 – 5 = 1
Amplitude ratio = 101
Earthquake B has a 10 times bigger amplitude

10. Example 2
If we compare two earthquakes; one (A) has a magnitude of 4.5 and the other (B) has a magnitude of 6.5 What is an amplitude ratio?
Magnitude difference = 6.5 – 4.5 = 2
Amplitude ratio = 102
Earthquake B has a 100 times bigger amplitude

11. Example 3
If we compare two earthquakes; one (A) has a magnitude of 3.7 and the other (B) has a magnitude of 6.7 What is an amplitude ratio?
Magnitude difference = 6.7 – 3.7 = 3
Amplitude ratio = 103
Earthquake B has a 1000 times bigger amplitude

12. Example 4
If we compare two earthquakes; one (A) has a magnitude of 4.3 and the other (B) has a magnitude of 6.7 What is an amplitude ratio?
Magnitude difference = 6.7 – 4.3 = 2.4
Amplitude ratio = 102.4
Earthquake B has a ~251 times bigger amplitude

13. Locating Earthquakes P and S waves travel at different speeds
Allows calculation of distance
Time-travel curve
Distance from multiple observations finds a location
Three seismographs

14. FIGURE 7. 11 How earthquake locations are determined
FIGURE 7.11 How earthquake locations are determined. (A) The distance from a seismic station to an earthquake is determined by using a
travel-time curve. Seismograms from two stations in Canada and one in Jamaica are fit to the travel-time curve so that the first arrival of P waves
(red arrows) and S waves (blue arrows) match the two curves on the graph. The distance to the earthquake from each seismic station is read off the
x-axis of the graph. Note that the surface waves in these three seismograms have been removed for simplicity. (B) A circle centered on each of the
three seismic stations is drawn on a map. The radius of each circle is the map distance to the earthquake from that station. The circles all intersect
at the location of the earthquake epicenter, in this case near Las Vegas, Nevada.

15. Earthquakes & Tectonic Plates
Where do earthquakes occur?
Convergent boundaries
Divergent boundaries
Transform fault boundaries
Plate interiors

16. Earthquakes & Tectonic Plates
Convergent boundaries
One plate sliding under another
Benioff zone
Friction along the down-plunging contact zone

17. Earthquakes & Tectonic Plates
Divergent boundaries
Friction along sliding blocks
Mainly shallow

18. Earthquakes & Tectonic Plates
Transform boundaries
Offsets ridge system
San Andreas fault zone
Strike-slip fault
Fault is vertical
Plate motion along the line of the fault
Fault creep

19. Earthquakes & Tectonic Plates
Plate interiors - infrequent
1811~12 in New Mardrid, MO
Area is still seeing deformation

20. Earthquake Hazard & Mitigation
Rock and soil – varying responses
Bedrock
Soil type
Topography
Liquefaction
Soil water content
Water table

21. Earthquake Hazard & Mitigation
Construction design and earthquake damage
Regulation of location and materials
Framing materials
Effects of affluence

22. Earthquake Hazard Map

23. Tsunami Seismic sea wave Undersea fault motion Far-traveling wave
Coastal hazard
Sumatra earthquake (2004)
Tohoku earthquake in Japan (2011)

24. FIGURE Evolution of the tsunami triggered by the 2011 Tohoku earthquake in Japan. (A) The initial fault rupture started about 32 kilometers below the seafloor (red dot) and propagated to the west (dashed red line), causing severe ground shaking in the Miyagi Prefecture. (B) The fault rupture switched directions and propagated eastward and upward, violently punching upward both the soft sediment near the seafloor and the deep water overlying it. (C) The resulting large bulge of water spread out, moving out to sea and towards the shore. In the deep water of the open ocean, the tsunami traveled rapidly as a series of relatively small waves detected by offshore buoys. Tsunami waves traveling shoreward grew larger as the bottom shallowed. (D) As they approached the shoreline, the tsunami waves became even larger and bunched up due to friction along the bottom. (E) The tsunami rushed onshore, causing death and destruction.

25. FIGURE Map of the tsunami triggered by the 2011 Tohoku earthquake in Japan. The tsunami traveled across the entire Pacific Ocean, taking over 21 hours to reach the coast of Chile. Note the thin strip of red along the west coasts of the Americas, indicating that the wave heights increased there due to the shallowing water depths.

26. Earthquake Prediction
Long-term prediction
Tells where earthquakes are likely to occur
Short-term prediction
Place and Time
Foreshocks
Aftershocks
Monitoring
China, Japan

27. Earth’s Interior Wave behavior
In homogeneous media, wave propagate equally in all directions
Velocity depends on the nature of material waves are traveling through
Waves refract (bend) when moving from one material to another

28. Earth’s Interior Moho discontinuity The crust-mantle boundary
Andrija Mohorovičić (1909)
Waves arrived at distant earthquakes faster than closer ones (Refraction)

29. Earth’s Interior Structure of the mantle 2900 km think
660 discontinuity
80 % of Earth’s volume

30. Earth’s Interior Discovery of the core A shadow zone of seismic waves
S wave does not propagate through the liquid medium  outer core is liquid.