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Earthquakes

Earthquakes. Movement & Destruction. What is an Earthquake?. Shaking of the Earth produced by a sudden movement of rock beneath its surface. How Do Earthquakes Occur? Elastic Rebound Theory. Deformation builds up and causes crust to bend. Elastic strain energy is stored.

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Earthquakes

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  1. Earthquakes Movement & Destruction

  2. What is an Earthquake? • Shaking of the Earth produced by a sudden movement of rock beneath its surface

  3. How Do Earthquakes Occur?Elastic Rebound Theory • Deformation builds up and causes crust to bend • Elastic strain energy is stored • When strain exceeds strength of the rock, it will “snap” into a new position • In the process of rupturing, energy is released in the form of “seismic waves”

  4. Where Do EQ Occur? • Fracture in the Earth’s crust where one side moves with respect to another • Faults

  5. Types of Fault

  6. Fault Terminology • Hanging wall • Footwall • Fault block below the fault • Fault block above the fault

  7. Normal Fault • Hanging wall moves down relative to the footwall • Exhibits lengthening or extension of the crust • Associated with fault block mountains • Horst – uplifted block • Graben – down dropped block • Basin and Range

  8. Basin and Range

  9. Reverse Fault • Hanging wall moves up relative to footwall • Exhibits shortening or compression of crust • Have dips > 45° • If dip’s < 45°, then thrust fault

  10. Strike-Slip Fault • Horizontal displacement • Types of Strike Slip: • Right lateral – As you face the fault, opposite side of plate moves right • Left lateral – opposite side of plate moves left

  11. San Andreas Fault

  12. Destruction from EQ • Ground Shaking • Tsunami • Fire • Liquefaction

  13. Destruction from EQ Ground Shaking • Rapid horizontal movement of ground may shift homes and cause them to collapse • Shaking is exaggerated in water-saturated or weak sediment

  14. Northridge, CA – 1994 M=6.7; 61 killed

  15. Destruction from EQTsunami • Giant Sea Waves generated by submarine EQ’s • Tsunamis travel 1,000’s of miles • Waves may reach 15 m (50 feet) in height and travel up to 960 km/hr (600 mph)

  16. Alaska - 1964 • M = 9.2; 125 died (110 tsunami, 15 EQ)

  17. Alaska, 1964 • There was so much uplift that once-submerged areas were exposed after EQ

  18. Indonesia 2004 • M=9.0; 280,000 killed

  19. Destruction from EQ’sFires • Many gas lines may break from the severe shaking • Unfortunately, many water lines may break as well so that firefighting becomes impossible

  20. M = 7.8; 3,000 killed San Francisco - 1906

  21. Destruction from EQ’sLandslides • Mountains usually form in areas of convergent boundaries • The steep slope are prone to landsides when shaken • Landslides are common following EQ’s in California

  22. Northridge - 1994 • Landslides prevalent in Santa Susana Mountains

  23. Destruction from EQ’s Liquefaction • Occurs when water-saturated is reorganized due to violent shaking • Sediment collapses, expelling water, and causes the ground to subside

  24. U.S. Earthquake Hazards

  25. San Andreas Fault

  26. Southern California Seismicity

  27. Southern California Faults

  28. Earthquake Predictions

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