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F orces within earth

Chapter 19.1 EARTHQUAKES. F orces within earth. Earthquakes . Natural vibrations of the ground caused by movement along fractures in the crust or volcanic eruptions Fractures form when stress exceeds the strength of the rock. Types of Stress. Tension- pull Compression- push Shear- twist

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F orces within earth

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  1. Chapter 19.1 EARTHQUAKES Forces within earth

  2. Earthquakes • Natural vibrations of the ground caused by movement along fractures in the crust or volcanic eruptions • Fractures form when stress exceeds the strength of the rock

  3. Types of Stress • Tension- pull • Compression- push • Shear- twist • Strain- deformation caused by stress

  4. Ductile Deformation • Elastic deformation occurs as a result of low stress • Ductile deformation occurs when stress is high • When does fracture occur?

  5. Faults • Fractures in the Earth’s crust along which movement occurs

  6. Types of Faults • Normal- tension • Reverse- compression • Strike-slip- shear

  7. Seismic Waves • (Primary) P-waves- squeeze and pull rocks in the same direction of the waves • (Secondary) S-waves- cause rock to move at right angles to the direction of the waves • Surface waves- cause rock to move up & down

  8. Focus- point where an earthquake originates • Epicenter- point on surface directly above the focus

  9. Chapter 19.2 EARTHQUAKES Seismic waves & earths interior

  10. Seismology • Study of earthquake waves • Seismograph/seismometer- register the vibrations • Seismogram- the record of vibrations

  11. Travel- time • Travel time for P and S waves differ • Can you tell which ones reach a location first? • Where is the biggest difference in the time one wave arrives before the other?

  12. Clues to Earth’s Interior • P waves are refracted in the core • S waves can not travel through liquids • Behavior of waves provide details of Earth’s interior structure and composition

  13. Chapter 19.3 EARTHQUAKES Measuring & locating earthquakes

  14. Earthquake Magnitude and Intensity • Magnitude- the amount of energy released during an earthquake • Richter scale- earthquake rating based on the size of the largest seismic waves • Increases by power of 10 for each magnitude

  15. Moment Magnitude Scale • Most used today • Based on the size of the fault rupture, amount of movement along the fault, and the rocks’ stiffness

  16. Modified Mercalli Scale • Based on the amount of damage done to structures • Measure of intensity

  17. Intensity Relates to Magnitude

  18. Locating an Earthquake • Distance from epicenter is calculated by comparing the separation time between P and S waves • 3 locations are needed to accurately determine the epicenter of the earthquake • Why?

  19. Seismic Belts • 80% occur in the Circum-Pacific Belt • 15% occur in the Mediterranean-Asian Belt

  20. Chapter 19.4 EARTHQUAKES Earthquakes & Society

  21. Earthquake Hazards • Structural Failure • Pancaking • Collapse 2010 Pichilemu earthquake in Chile 1999 Izmit earthquake in Turkey

  22. Earthquake Hazards • Land and Soil Failure • Liquifaction • Seismic wave amplification

  23. Liquifaction in Christchurch, NZ

  24. Earthquake Hazards • Fault Scarps • Vertical offset

  25. Earthquake Hazards • Tsunamis

  26. Seismic Risk

  27. Earthquake Prediction • History • Strain Accumulation

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