Crust

1. Crust • Outermost layer or shell of the Earth • Crust represents less than 0.1% of the Earth's total volume

2. Mantle • The zone of the Earth below the crust and above the core • Divided into the upper mantle and the lower mantle, with a transition zone between

3. Lithosphere • The solid portion of the Earth, as compared with the atmosphere and the hydrosphere • Includes the crust and part of the upper mantle and is of the order of 100 km in thickness

4. Stress • Stress is a force that is capable of greatly deforming rocks, and may result in folding or faulting of rock, and even to the building of mountains

5. Types of Stress • There are three types of stress • Compression • Tension • Shearing

6. Compression • Opposing forces directed inward along a single line • Compression shortens an object along the axis of compression, and thickens it in the directions perpendicular to the stress direction After Before

7. Tension • Tension is the result of divergence, pulling an object in opposite directions along a common axis • Tension lengthens an object along the axis of tension, and thins it in the perpendicular directions After Before

8. Tension Crack Pictures • Nisqually Earthquake, 2/28/01, in Washington caused tension cracking.

9. Shear • Opposing stress is created by two plates moving in opposite directions

10. Deformation • Rocks subjected to stress may: • Fracture or crack • Fold • Fault, movement along break

11. Why do some rocks fold/fault?

12. Anticline • If the fold is convex upward, it is called an anticline

13. Anticlinal Fold • Rainbow Gap, Virginia • Photo: Henry Johnson

14. Atlas Mountains Anticline • One of the best exposures of a complexly folded mountain belt anywhere occurs in the Atlas Mountain system of northwest Africa

15. Syncline Syncline • If the fold is convex downward, it is called a syncline

16. Syncline Photo • Photo: Duncan Heron • Synclinal fold exposed by roadcut

17. Anticline-Syncline Pair • Anticline-Syncline pair in Devonian Old Red Sandstone. SW Wales, UK • Note the different fold shapes

18. Domes • Domes are uplifted areas • Caused by magma pushing up on the crust

19. Eroded Dome, Sinclair, Wyoming

20. Faults • A fault is a fracture along which definite movement has occurred

21. Fault Terminology • Foot Wall and Hanging Wall are borrowed from mining terminology • Ore veins are often deposited along faults

22. Strike Slip Fault Photo: Arthur G. Sylvester. San Jacinto fault, Anza, Southern California

23. Right-Lateral Strike Slip • Block is displaced to the right, looking across the fault

24. Strike Slip FaultsRight Lateral • Near Coos Bay, Oregon

25. Left-Lateral Strike Slip • Block is displaced to the left, looking across the fault

26. Strike Slip Faults - Left Lateral • Near Lillooet, British Columbia

27. Normal Fault • Normal faulting results from tensional forces • Hanging wall moves down relative to the footwall (here, to the right) • Places younger rocks on top of older

28. Sevier Normal Fault

29. Death Valley Normal Faults

30. Reverse Fault • Reverse faulting results from compressional forces • Hanging wall moves up relative to the footwall (here, to the left) • Places older rocks on top of younger

31. Reverse Fault • Reverse faults and associated fold

32. Thrust Fault • Thrust faults are low angle reverse faults • They sometimes move large distances (tens of kilometers)

33. Lewis Overthrust

34. Explanation of Lewis Overthrust • Chief Mountain was moved about forty kilometers and isolated by erosion • Chief Mountain is much older (Precambrian) than the rock upon which it rests (Cretaceous)

35. Chief Mountain Older rock above younger, typical of thrust faults Glacier National Park, Montana

36. Rift valleys and Fault block mountains

37. San Andreas Fault • Pacific plate, left • North America, right

38. San Andreas Offsetting Fence

39. Mountain building • Tectonic forces often create mountains, a process called orogeny • There are several types of mountains • Folded • Faulted • Upwarped • Volcanic

40. Folded mountains • Plate collisions involving continental plates can produce high mountains • Examples: • Himalayas (India, Tibet, China) • Alps (Europe) • Urals (Europe/Asia boundary) • Appalachians

41. Himalayan Mountains High peaks in the Himalayas Mt. Everest

42. Owens Valley and the Sierra Nevada Range

43. Volcanic Mountains

44. Isostasy • The condition of equilibrium, comparable to floating, of the units of the lithosphere above the asthenosphere • Crustal loading, as by ice, water, sediments, or volcanic flows, leads to isostatic depression or downwarping • Crustal unloading, as by erosion, or melting of ice, to isostatic uplift or upwarping

45. Isostasy Diagram

46. Earthquake • A sudden motion or trembling in the Earth caused by the abrupt release of slowly accumulated strain • Strain is a change in the shape or volume of a body as a result of stress

47. Focus • The initial rupture point of an earthquake, where strain energy is first converted to elastic wave energy • The point within the Earth which is the center of an earthquake

48. Epicenter Focus Epicenter • The point on the Earth's surface that is directly above the focus of an earthquake

49. Seismograph • An instrument that detects, magnifies, and records vibrations of the Earth, especially earthquakes • The resulting record is a seismogram

50. Principle of the Modern Seismograph