Earthquakes

1. Earthquakes Earth Science chapters 5 and 6 Earth Science Chapters 5 and 6

2. Earth’s interior • Crust – thin layer of solid rock including dry land and ocean floor • Mantle – rock that is very hot, but solid • Outer core – liquid metal • Movements may cause magnetic field • Inner core – dense, solid metal Earth Science Chapters 5 and 6

3. Wegener’s hypothesis • 1910 • All continents were once joined together in a single landmass and have since drifted apart • Pangea – supercontinent • About 300 million years ago • When reptiles and winged insects first appeared • Later broke apart and drifted Earth Science Chapters 5 and 6

4. Wegener’s proof – p. 138 - 139 • Land features • Mountain ranges and coal fields line up • Fossils • Plant fossils found on widely separated landmasses • Freshwater reptile fossils found in places now separated by oceans • Climate • Evidence that continents that are now cold were once tropical, and vice versa Earth Science Chapters 5 and 6

5. Rejection • Wegener’s hypothesis was rejected in his time. • He was unable to explain how continents moved. • He challenged the theories of mountain formation at the time. • Later evidence supported his theory. Earth Science Chapters 5 and 6

6. Plate tectonics • Explains the formation, movement, and subduction of Earth’s plates • Movement caused by motion in the mantle • Plates collide, pull apart, or grind past each other • Changes Earth’s surface Earth Science Chapters 5 and 6

7. Divergent boundaries • Where two plates move apart • Creates mid-ocean ridges and rift valleys Earth Science Chapters 5 and 6

8. Convergent boundaries • Where two plates come together • Plates collide • One plate is subducted beneath the other • Forms mountains or ocean trenches Earth Science Chapters 5 and 6

9. Transform boundaries • Where two plates slip past each other moving in opposite directions • Often causes earthquakes Earth Science Chapters 5 and 6

10. Discuss • Describe Earth’s interior. • Describe the three different types of plate boundaries. Earth Science Chapters 5 and 6

11. Stress • Force that acts on a rock to change its shape or volume • Many rocks can bend or fold, but they eventually break Earth Science Chapters 5 and 6

12. Tension • Stretches rock by pulling on crust • Rock gets thinner in the middle • Happens when two plates move apart • Divergent boundaries Earth Science Chapters 5 and 6

13. Compression • Squeezes rock until it folds or breaks • Happens when two plates come together • Convergent boundaries Earth Science Chapters 5 and 6

14. Shearing • Pushes rock in two opposite directions • Can cause rock to break apart or change its shape • Happens at transform boundaries Earth Science Chapters 5 and 6

15. Fault • Break in rock where surfaces slip past each other • Mostly along plate boundaries Earth Science Chapters 5 and 6

16. Normal fault p. 164 • Fault at an angle • One block of rock is below the fault • Footwall • One block of rock is above fault • Hanging wall • Hanging wall slips downward • Falls downhill • Where plates diverge • Forms valleys Earth Science Chapters 5 and 6

17. Reverse fault p. 165 • Where plates converge • Same structure as normal fault, but opposite motion • Hanging wall slides up • Moves uphill • Forms mountains Earth Science Chapters 5 and 6

18. Strike-slip fault p. 165 • At transform boundaries • Plates slip sideways with little or no vertical motion • Often causes earthquakes Earth Science Chapters 5 and 6

19. Folded crust • Wrinkles • Makes mountains • Anticline • Fold that bends upward (mountain) • Syncline • Fold that bends downward (valley) Earth Science Chapters 5 and 6

20. Plateau • Large area of flat elevated land • Can be formed by forces lifting Earth’s crust Earth Science Chapters 5 and 6

21. Discuss • What are the three main types of stress in rock? • Compare and contrast the way that compression affects the crust to the way that tension affects the crust. Earth Science Chapters 5 and 6

22. Earthquake • The shaking and trembling that results from the movement of rock beneath Earth’s surface • Often too small to notice • Releases a lot of stored energy in a few seconds Earth Science Chapters 5 and 6

23. Focus • Where the rock beneath the surface that is under stress breaks Earth Science Chapters 5 and 6

24. Epicenter • On surface directly above the focus Earth Science Chapters 5 and 6

25. Seismic waves • Carry energy away from the focus • Through Earth’s interior • Along Earth’s surface Earth Science Chapters 5 and 6

26. P waves • Primary waves • Arrive first (travel fastest) • Compressional or longitudinal waves • Can damage buildings Earth Science Chapters 5 and 6

27. S waves • Secondary waves • Arrive second • Transverse waves • Vibrate up and down and side to side • Shake ground back and forth • Shake structures violently • Cannot travel through liquid Earth Science Chapters 5 and 6

28. Surface waves • May occur when P and/or S wave reach the surface • Move the slowest • Can be the most destructive • Can make the ground roll like ocean waves • Can shake buildings side to side Earth Science Chapters 5 and 6

29. Mercalli scale • Rates earthquakes according to level of damage at a given place • Numbered from I to XII • See page 173 Earth Science Chapters 5 and 6

30. Richter scale • Rates earthquake’s magnitude (size) • Based on seismograph readings of seismic waves • Accurate for small, nearby earthquakes • Less accurate for large or distant earthquakes Earth Science Chapters 5 and 6

31. Moment magnitude scale • Estimates the total energy released by an earthquake • Can be used on any earthquake • Based on info from seismographs • On the news when they say Richter scale, it usually is really the moment magnitude scale Earth Science Chapters 5 and 6

32. Magnitudes • Each one-point increase in magnitude represents the release of about 32 times more energy. • A magnitude 5 quake releases 32 times as much energy as a magnitude 4, about 1024 times as much as a magnitude 3, about 32768 times as much as a magnitude 2, and about 1048576 times as much as a magnitude 1 Earth Science Chapters 5 and 6

33. Magnitudes • Below magnitude 3 is rarely noticed by people • Below 5 are small and cause little damage • Between 5 and 6 cause moderate damage • Above 6 cause great damage • Above 8 are extremely rare • During 1900s only two quakes above 9 • Chile in 1960 • Alaska in 1964 Earth Science Chapters 5 and 6

34. Chile 1960 • Magnitude 9.5 • Highest recorded Earth Science Chapters 5 and 6

35. Alaska 1964 • 2nd highest • 9.2 Earth Science Chapters 5 and 6

36. Locating epicenter • Measure difference in arrival times of P waves and S waves • Use data from at least three stations • Draw circles out from each station • Epicenter is where circles cross Earth Science Chapters 5 and 6

37. Discuss • What kind of movement is produces by each of the three types of seismic waves? • In what order to seismic waves arrive? • What is an earthquake’s magnitude? Earth Science Chapters 5 and 6

38. Seismograph • Rotating drum moves with vibrations • Attached to ground • Weighted pen does not • Weight resists motion • Modern seismographs use electronic sensors instead of pens Earth Science Chapters 5 and 6

39. Seismogram • Record of seismic waves produced by seismograph • P waves first • S waves next • Surface waves largest spikes Earth Science Chapters 5 and 6

40. Monitoring faults • Check for slight rise or fall in elevation or tilt of land • Helps predict earthquakes Earth Science Chapters 5 and 6

41. Tiltmeter • Measures tilting or raising of ground • Like levels • Contain two liquid-filled bulbs connected by a stem • Liquid level in each is monitored Earth Science Chapters 5 and 6

42. Creep meter • Measures horizontal movement of ground • Uses wire stretched across a fault • One end attached to post • Other end attached to a weight that can slide • Amount of sliding measured Earth Science Chapters 5 and 6

43. Laser-ranging device • Detects horizontal movements • Times a laser beam as it travels to a reflector and back • If the time changes, that means the reflector has moved Earth Science Chapters 5 and 6

44. GPS satellite • Measures change in elevation and horizontal movement • Measures tiny movements in markers set up on either side of a fault Earth Science Chapters 5 and 6

45. Finding faults • Often hidden beneath rock • Seismic waves reflected off faults • Helps determine earthquake risk Earth Science Chapters 5 and 6

46. Using Friction • Friction • The force that opposes the motion of one surface as it moves across another • Low friction means stress doesn’t build up, so big earthquakes are unlikely • Moderate friction produces occasional small earthquakes • High friction causes stress to build up and can cause bigger earthquakes Earth Science Chapters 5 and 6

47. Predicting earthquakes • Not very accurate yet • Better at finding the probability of a strong earthquake occurring • But not when it will occur Earth Science Chapters 5 and 6

48. Discuss • A seismograph records a strong earthquake and a weak earthquake. How would the seismograms for the two earthquakes compare? • What four instruments are used to monitor faults? Earth Science Chapters 5 and 6