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Part 8: Fold Types

Part 8: Fold Types. Compressive Stress. Shear Stress. Tensional Stress. Orientation of stress leads to different folds. Ductile Strain. Earthquakes. Stanford, 1906. Compressive Stress. Tensional Stress. Shear Stress. Earthquakes occur on faults. Active Fault. Faults.

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Part 8: Fold Types

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  1. Part 8: Fold Types

  2. Compressive Stress Shear Stress Tensional Stress Orientation of stress leads to different folds

  3. Ductile Strain

  4. Earthquakes Stanford, 1906

  5. Compressive Stress Tensional Stress Shear Stress

  6. Earthquakes occur on faults Active Fault

  7. Faults Faults are fractures with movement

  8. Faults Faults are fractures with movement

  9. STRESS BUILDS UNTIL IT EXCEEDS ROCK STRENGTH Local rock strength Stress Time Earthquakes

  10. STRESS BUILDS UNTIL IT EXCEEDS ROCK STRENGTH Earthquakes are the result of stress that builds up over time. Local rock strength Stress Time Earthquakes

  11. STRESS BUILDS UNTIL IT EXCEEDS ROCK STRENGTH Earthquakes are the result of stress that builds up over time. Stress gradually builds as tectonic forces deform rocks. Local rock strength Stress Time Earthquakes

  12. STRESS BUILDS UNTIL IT EXCEEDS ROCK STRENGTH Earthquakes are the result of stress that builds up over time. Stress gradually builds as tectonic forces deform rocks. When the stress exceeds the strength of the rocks… Local rock strength Stress Time Earthquakes

  13. STRESS BUILDS UNTIL IT EXCEEDS ROCK STRENGTH Earthquakes are the result of stress that builds up over time. Stress gradually builds as tectonic forces deform rocks. When the stress exceeds the strength of the rocks… …the fault slips, causing an earthquake. Local rock strength Stress Time Earthquakes

  14. STRESS BUILDS UNTIL IT EXCEEDS ROCK STRENGTH Earthquakes are the result of stress that builds up over time. Stress gradually builds as tectonic forces deform rocks. When the stress exceeds the strength of the rocks… …the fault slips, causing an earthquake. Local rock strength The process repeats again and again. Stress Time Earthquakes

  15. 0 Seconds Rupture expands circularly on fault plane, sending out seismic waves in all directions. Focus Fault cracks at surface 5 Seconds Rupture continues to expand as a crack along the fault plane. Rocks at the surface begin to rebound from their deformed state. Fault crack extends 10 Seconds The rupture front progresses down the fault plane, reducing the stress. 20 Seconds Rupture has progressed along the entire length of the fault. The earthquake stops.

  16. World seismicity from 1976 to 2002 ASIA EUROPE NORTH AMERICA PACIFIC OCEAN ATLANTIC OCEAN AFRICA SOUTH AMERICA INDIAN OCEAN AUSTRALIA ≤ 50 km deep (shallow focus) 50–300 km deep ANTARCTIC OCEAN ≥ 300 km deep (shallow focus)

  17. Plate Boundaries and Faults • Strike-slip faults along transform boundaries • Reverse faults along convergent boundaries • Normal faults along divergent boundaries

  18. Strike-Slip Faults: Transform Boundary • San Andreas Fault • Several magnitude 7 earthquakes recently • usually occur in clusters • arrows show motion/yr

  19. Faults not always parallel to boundary Results in uplift of mountains

  20. Denali fault, Alaska Mt. McKinley

  21. Offset streams along the San Andreas Fault in the Carrizo Plain, CA

  22. Southern California fault traces San Andreas fault San Gabriel Mountains North American Plate Pacific Plate Los Angeles Motion of Pacific Plate relative to motion of North American Plate

  23. Southern California fault traces Here, the San Andreas fault is parallel to plate motion, and the faulting is right-lateral strike slip. San Andreas fault San Gabriel Mountains North American Plate Pacific Plate Los Angeles Motion of Pacific Plate relative to motion of North American Plate

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