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Sec 3 Geo: Introduction to Earthquakes
Earthquakes occur along fault lines when built-up stress in rocks is suddenly released. They can happen at plate boundaries where plates converge, diverge, or move past each other. The type and extent of damage from earthquakes depends on factors like the depth of the focus, distance from the epicenter, underlying soil and preparedness of people in the affected area. Some choose to remain in quake-prone regions due to acceptance of risks or ability to adapt infrastructure. Major historical quakes include those in Sumatra, Japan, Sri Lanka, and San Francisco.
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Sec 3 Geo: Introduction to Earthquakes
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- 3. What are they? •A vibration in the earth’s crust caused by the sudden release of stored energy in the rocks found along fault lines • Occurs when there is plate movement along plate boundaries
- 4. Where do theyoccur? • They can occur on convergent/divergent/transform plate boundaries • Occur most on convergent plate boundaries because the stress builds up when a plate subducts beneath another
- 5. How do theyform? • Jagged sides of the plates cause the plates to be stuck when they try to slide past each other. • The friction of movement builds up stress in the rocks. When they continue to move, more stress builds up. • When they can no longer withstand the increasing stress, they can slip many metres, • releasing massive amounts of stored energy in the form of seismic waves, which is an earthquake
- 6. Epicenter: The pointon the earth’s surface directly above the focus Focus: The point of sudden energy release
- 7. Types of earthquakes Typeof earthquake Deep-focus earthquake Shallow-focus earthquake Location of focus • Occurs between 70-700km below earth’s surface • Occurs in the upper 70km of earth’s crust Impact on land • Smaller impact on land as vibrations/seismic waves take a longer time to reach the surface and would have lost most energy by then • Greater impact on land as the vibrations/seismic waves reach the land surface more quickly
- 8. Extent of earthquakes •Population density • Level of preparedness • Distance from the epicentre • Time of occurrence • Type of soil
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- 11. Banda Aceh, Sumatra,Indonesia
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- 17. What affects the extentof earthquakes? Psst.. Points are found on pages 31-32.
- 20. Why do peoplecontinue to live in area prone to earthquakes? • Fatalistic approach • Acceptance approach • Adaptation approach
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