1. CHAPTER 12: EARTHQUAKES

2. Earthquakes
An Earthquake is a sudden shaking of the crust

3. What causes earthquakes?
Most earthquakes are associated with the breakage and displacement of rocks, often along a known fault
Kinetic energy is released as seismic waves
Seismic waves radiate through the Earth's interior resulting in "shaking“ at surface

4. (potential for casualties and infrastructure damage is high)
More than 380 major cities lie on or near unstable regions of the Earth’s crust
(potential for casualties and infrastructure damage is high)
How do earthquake locations relate to plate boundaries? Identify some of the plates on this map.

5. There Are Several Types of Earthquake Hazards
Ground shaking produces sediment liquefaction (instability of the ground), mass wasting (landslides), and damage to buildings and other structures
Fires following an earthquake can be catastrophic and fire-fighting capabilities may be compromised
Often water lines and emergency equipment are damaged and utility and communications systems are disrupted
A tsunami may be generated
Please insert a button for Tsunami Simulation of a tsunami
Suggested tips to give students: After the 1995 earthquake in Kobe, Japan; a clever engineer modified the mechanism that triggers an airbag in a vehicle so it could be used on residential gas meters. The new mechanism automatically shuts off the gas flow to individual homes when sufficiently shaken by an earthquake (i.e. in the hopes of preventing fires).
Tsunami Simulation Animation

6. Explain how an earthquake could lead to flooding.
Kashmir, 2005
Suggested tips to give students: The Hill Country of Texas is “hilly” because there is a huge “batholith” (cooled, solidified, underground magma chamber) that uplifted the overlying rocks. Enchanted Rock (similar to the exfoliation dome pictured) is like a “pimple” on this batholith.
Explain how an earthquake could lead to flooding.

7. Natural Resources Canada map of seismic shaking hazards
What is the relative earthquake risk in your part of the country?

8. The Elastic Rebound Theory
The elastic rebound theory explains the origin of earthquakes
Energy is stored in the form of elastically deformed rock. When the strain exceeds the strength of the rock it breaks the energy is released.

9. Is this a normal or a reverse fault?
Strain Release
Eventually the rock is no longer able to accommodate the buildup of strain and it ruptures, either along a pre-existing fault or at a new location.
Is this a normal or a reverse fault?

10. What are the definitions of “focus” and “epicenter”?

11. Clusters
Earthquakes tend to occur in clusters, both in time and in space.

12. Intraplate Earthquakes
Most seismicity occurs at plate boundaries,but intraplate earthquakes are also common
Identify some intraplate earthquakes on this map.

13. Divergent, convergent, and transform margins
Divergent, convergent, and transform margins are the sites of frequent earthquake activity
Divergent margin
Convergent margin
Intraplate location
Transform margin

14. Identify some divergent, convergent and transform boundaries on this map where there have been earthquakes.

15. Intraplate Earthquakes
Poorly understood
Most have shallow foci
Tend to occur in soft, weak areas of plate interiors, caused by stresses transmitted from plate boundaries,
Reactivation of old rift zones or faults (e.g., Logan Fault)
Hot Spots
Yellowstone
Hawaii

16. Divergent Seismicity

17. Convergent Seismicity
The zone of seismicity along the plane of the subducting plate is called the Wadati-Benioff Zone

18. Where can you see some Wadati-Benioff zones on this map?
Which plates are involved?

19. Transform Seismicity
What are some features that the San Andreas and North Anatolian Faults have in common?

20. Earthquakes produce four types of seismic waves
Two types of Body Waves and two types of Surface Waves

21. Body waves (within the crust)
Surface waves

22. Liquids do not resist changes in shape - they absorb S waves rather than transmit them.

23. A Seismogram is produced by a Seismometer

24. Seismometers
Seismometers are instruments that measure and help locate earthquakes
An earthquake near Vancouver is measured by a seismometer in Saskatoon

25. Could an earthquake be located with just two seismic stations?
Seismometers in Iqaluit, Halifax and St. John’s are used to locate an earthquake in central Quebec
Could an earthquake be located with just two seismic stations?
In fact, many seismometers are used to locate earthquakes.

26. Expressing Earthquake Magnitude
Earthquake magnitude is expressed as a whole number and a decimal fraction (e.g., 7.3)

27. Modified Mercalli (MM) intensity scale
Intensity is expressed using the Modified Mercalli (MM) intensity scale
What is the difference between earthquake magnitude and intensity?

28. Magnitude of an earthquake using the Richter method

29. Comparison of energy released and damage done by different events

30. Seismology
Seismology is the study of seismic waves in order to improve our understanding of the Earth’s interior
Wave refraction is used to identify a discontinuity

31. P-wave and S-wave shadow zones
Why are S waves not transmitted through the Earth’s core?

32. Seismic Data
Seismic data confirm the existence of discontinuities in Earth’s interior

33. Mohorovicic Discontinuity
~ 8 km beneath oceanic basins
~ 20 to ~70 km beneath continents

34. This map shows just a small fraction of all of the seismometers on Earth.

35. Seismic Tomography
Seismic tomography uses seismic data from hundreds of seismic stations and hundreds of different earthquakes to provide a 3-dimensional seismic velocity image of the Earth’s interior.

36. Modeling with Tomographic Images
Why is the subducted Farallon Plate in the mantle beneath North America represented by a zone of higher seismic velocity than the surrounding mantle?

37. COPYRIGHT
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