How it happens..........

1. EARTHQUAKE ! By Deepak

6. Earthquake map

10. Map views of bottom half of focal spheres

11. What does the focal mechanism for a strike-slip earthquake look like?

12. What does the focal mechanism for a strike-slip earthquake look like?

13. FOCAL MECHANISMS AND TECTONICS What is the relative motion? How many plates are shown?

14. If earthquakes occur along these plate boundaries, what will the focal Mechanisms look like?

17. SHOW TECTONIC MAP

19. Chinese Seismoscope - first earthquake sensor

21. Seismograms from many stations for one earthquake

22. Earthquake Location if P and S-wave data are available

23. What if you only have P-wave arrivals at three seismometers… Can you locate the quake? Station: Arrival Time A 10:22:04 B 10:22:04 C 10:23:34

25. Interior of the Earth Almost everything we know about the deep interior of the earth comes from the study of seismic waves

28. Seismic velocities and density changes in the earth

31. LONG-TERM Predictions (years to decades) are based on tectonic indicators - fault activity, distance to active faults, seismic gaps etc INTERMEDIATE-TERM: (Year to days) based on increased activity in an area SHORT-TERM: (Day to hours) very difficult, but very valuable Predictions should include STATISTICS, such as: “ There is an 80% probability that a magnitude 7.5 or larger earthquake will occur in the San Francisco area within the next two weeks.”

32. WHAT HAPPENS IF YOUR PREDICTED QUAKE DOESN’T HAPPEN? Law suits. WHAT HAPPENS IF IT’S BIGGER OR SMALLER OR OCCURS EARLIER OR LATER OR IN A DIFFERENT LOCATION? Law suits.

34. Elastic Rebound Theory

37. What if only the Maximum Strain is fixed? In this case, the TIME of the next quake will be predictable, but the SIZE will not be. Small quake LARGE quake

38. What if only the Minimum Strain is fixed? In this case the SIZE of the next quake can be predicted - if it happens tomorrow, but WHEN it occurs is not constrained.

39. Let’s Try an experiment to see if either of these assumptions hold with a SIMPLE earthquake model… Turning the crank represents the passage of time, and the spring stretches (representing strain across the fault) until the weight moves - representing an earthquake.

40. What information do we need? We need to measure the length “A” to get our measure of how much time has passed, and We need to measure the length “B” to see how large the earthquakes are. “B” only changes during an earthquake. A-B is a measure of strain, and A is a measure of time, so, from these two measurements, we can make plots of strain vs. time and check our hypotheses.

41. If we plot “A” along the x axis and “B” along the y axis we get plots like: If we plot “A” along the x axis and “A-B” along the y axis we get plots like:

45. Damage is caused by things falling on you from above

47. Adobe is NOT a good building material in earthquake-prone areas.

48. LOMA PRIETA, I 80

50. Alaska, 1964: Often the GROUND fails, not the building. Build on HARD ROCK!

52. KOBE

53. San Francisco Area Earthquakes

55. Before the earthquake and fire

58. Buildings built on soft fill often collapsed.

59. Much damage in 1989 earthquake occurred in soft fill Where the 1906 trash had been dumped into the bay.

60. Seismogram wiggle size Vs. earthquake magnitude

64. Thank you