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Introduction to Faults

Introduction to Faults. What is a fault ? A fault is a break or crack in Earth ’ s crust along which rocks shift their position. San Andreas Fault, California. Describing a fault: Fault Line Fault Plane Foot Wall Hanging Wall. Plate Boundary: Divergent. Fault Type: Normal.

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Introduction to Faults

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  1. Introduction to Faults

  2. What is a fault? A fault is a break or crack in Earth’s crust along which rocks shift their position. San Andreas Fault, California

  3. Describing a fault: • Fault Line • Fault Plane • Foot Wall • Hanging Wall

  4. Plate Boundary: Divergent

  5. Fault Type: Normal Occurs when two blocks are being pulled apart

  6. Plate Boundary: Convergent

  7. Fault Type: Reverse Occurs when two blocks are being pushed apart

  8. Plate Boundary: Transform

  9. Fault Type: Strike-slip Occurs when two blocks slide past one another.

  10. Each type of plate boundary has a type of faulting that it primarily accommodates.

  11. P-waves S-waves Surface waves

  12. P-waves • primary wave • compression wave • fastest of the seismic waves • can travel through solids, liquids, and gases • Surface waves • 2 types: Love waves and Rayleigh waves • Slowest seismic waves • May cause the greatest damage in an earthquake Seismic waves S-waves • secondary wave • shear wave • second-fastest seismic wave • can only travel through solids

  13. Travel time from San Diego to Los Angeles P-waves 25 seconds S-waves 41 seconds Surface waves 50 seconds

  14. Types of Seismic Waves: P-wave, S-wave, surface wave P and S waves travel through the Earth (and even into the core!) Surface waves travel along Earth’s surface

  15. Elastic Rebound

  16. What is happening to the Pacific plate and the North American plate? What happens along the fault?

  17. Elastic Rebound Theory Fault Fence Original position Stress Accumulates Earthquake: stress released Rebound to original shape

  18. Elastic Rebound Theory 1. Stress on a fault slowly accumulates 2. During an earthquake, stress on the fault is released 3. After an earthquake, stress begins to re-accumulate

  19. At the plate boundary If a fence is built across the fault, what will happen to the fence as time passes? The fence will slowly bend as the sides of the fault move.

  20. Eventually an earthquake occurs:

  21. At the plate boundary:When the earthquake occurs, the fence will break.

  22. After the earthquake, the process starts again.

  23. Elastic Rebound: the sudden return of elastically deformed rock to its undeformed shape Elastic Rebound is the mechanism for producing earthquakes.

  24. Fault Zones Fault zone: a region of numerous, closely spaced faults

  25. What’s happening in CA?

  26. Will CA break off and fall into the ocean?

  27. Faults in Southern California

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