FAULTING

1. FAULTING

2. DEFINITION • Fractures in which noticeable movement has occurred

3. CAUSE OF FAULTS? • Stress – forces at work on the earth • Three kinds • Tensional • Compressional • Shearing

5. Animation of stress • http://scign.jpl.nasa.gov/learn/plate5.htm

6. DEFORMATION • Elastic • Return to their original shape after the stress is removed • Plastic • Once stress is removed, the deformation remains Once this limit is passed, the rock will break – fault is produced

7. TENSIONAL • ‘Pulling apart’ • Type of fault produced • Normal fault

8. COMPRESSIONAL • ‘Pushing together’ • Type of fault produced • Reverse • Thrust

9. SHEARING • Sliding opposite each other • Type of fault produced • Strike-slip (lateral)

10. Why do some rocks fault when others fold? • Elasticity of the rock material • Ductile material – limestones and clays • Brittle material – sandstones and granites • Amount of stress • Speed that the stress is applied

11. ANTICLINE

12. SYNCLINE

15. NAMING FAULTS • When the ground breaks, sections are moving with respect to each other • The ground above the fault = Hanging Wall • The ground below the fault = Footwall

16. Normal Fault • Tensional (pull apart) stress • Allows the hanging wall to slide down

17. Reverse Fault • Compressional (pushing) Stress • Causes the hanging wall to move up

18. Thrust Fault • Stress is still compressional (pushing), but the fault lies at a low angle. • Now the hanging wall gets pushed up and over the footwall

19. Strike-Slip Fault • Shearing (scissor-type) stress causes one block to slide past the other • Two types – right and left lateral

20. FAULT ANIMATIONS • http://www.iris.edu/gifs/animations/faults.htm • ACTIVITY: Use play dough to model this movement

24. EARTHQUAKES

25. EARTHQUAKES • The breaking of rocks produces vibrations – known as earthquakes • Generates seismic waves • Originate at the focus – point underground where the fault starts • Travel outward in all directions

27. Do EQ produce more EQ’s? • Linear Seismicity • Big Bear Animation

28. How are far away earthquakes detected? • First seismographs • In 132, Zhang Heng in China Han dynasty, invented the first seismometer • Called Houfeng Didong Yi = ‘instrument for measuring the seasonal winds and the movements of the Earth’

29. How do modern seismographs work?

30. Basic principles • A frame securely affixed to the earth. • The foundation is critical, and often the most expensive part of a seismic station. • An inertial mass suspended in the frame by some method, using springs or gravity to establish a steady-state reference position. • A damper system to prevent long term oscillations in response to an event. • A means of recording the motion or force of the mass relative to the frame.

31. Passing seismic waves move the frame, while the mass tends to stay in a fixed position due to its inertia. • The seismometer measures the relative motion between the frame and the suspended mass.

33. SEISMIC WAVES • When seismic energy is released from this break in the rock • Three Main Types • Primary (P-waves) • Fastest, travels through solids and liquids • Secondary (S-waves) • Second fastest, travels only through solids • Surface (L-waves) • Travels along the surface • Cause the most destruction

34. Seismic Players Activity • VOLUNTEERS PLEASE? • Tie this activity back to what students learned about molecular structure of solids and liquids

35. Other Activities to show Seismic Energy • Using Slinkies • http://web.ics.purdue.edu/~braile/edumod/slinky/slinky.htm • ANIMATIONS • http://www-rohan.sdsu.edu/~rmellors/lab8/l8maineq.htm#rwave

36. Visualizing seismic energy • How does the energy travel through the earth? • http://www.pbs.org/wnet/savageearth/animations/earthquakes/main.html

37. How does this energy affect buildings? • Boss Model Assembly • Illustrates how the size and shape of buildings influences the way that they will react to ground motion • For instructions on how to assemble: http://www.wested.org/werc/earthsystems/geology/boss.html

39. Measuring Earthquake Strength • Magnitude vs Intensity • Magnitude is mathematical computations from seismograms • Will always be the same no matter how far away you are from the epicenter • Intensity will vary from location to location • The closer you are, the more the ground will shake.

40. INTENSITY • Measure Intensity with Mercalli Scale • Interviews and investigations, see where the most damage occurred • Mark Twain Narrative handout • Mercalli Scale handout

41. Oct. 17, 1989 Loma Prieta

42. Intensity of shaking decreases with distance from epicenter (MM Intensity scale). M6.7, 1994 Northridge, California earthquake

43. Intensity of shaking decreases with distance from epicenter (star; USGS Shake Map). M6.7, 1994 Northridge, California earthquake

44. Did you feel it? • http://earthquake.usgs.gov/eqcenter/dyfi.php • Website managed by the USGS where you can log in and record what you felt. • They will create an intensity map based on this information.

45. MAGNITUDE • Measured with the Richter Scale • Developed in 1935 by Charles Richter in collaboration with Beno Gutenberg, both of the California Institute of Technology • the scale was originally intended to be used only in a particular study area in California, and • on seismograms recorded on a particular instrument, the Wood-Anderson torsion seismometer

46. Richter Scale A measure of the magnitude of an earthquake at its epicenter. Each point increase on the Richter scale is a 30 times increase in the magnitude.

47. Seismic Moment Scale • Introduced in 1979 by Tom Hanks and Hiroo Kanamori • Relates to the physical parameters • dimension of the earthquake rupture, and • the energy released from the earthquake

48. Seismograph Information

49. How do scientists find the epicenters of earthquakes?

50. HOMEWORK: On-line Activity • http://www.sciencecourseware.org/VirtualEarthquake/VQuakeExecute.html • Go to this website and plot all three earthquake epicenters and magnitudes • Plot the certificate and bring back to class