G8 Science Q2- Week 2-3- Epicenter and Focus of Earthquake.pptx

Science 8 Quarter Week 3 Locate Focus, Epicenter and Fault Line

1. Earthquakes PREPARED BY: TYPE YOUR NAME HERE

2. S8ES -IIa - 14 Using models or illustrations, explain how movements along faults generate earthquakes

3. Causes - tectonics and faults Magnitude - energy and intensity Earthquake geography Seismic hazards - shaking, etc. Recurrence - frequency and regularity Prediction? Mitigation and preparedness

4. Causes: accumulated strain leads to fault rupture - the elastic rebound model

5. Styles of faulting

6. Causes : fault movement releases energy as seismic waves radiating from rupture Seismic waves

7. Seismic wave forms

8. Earthquake magnitude: scales based on seismograms M L =local (e.g. Richter scale) - based on amplitude of waves with 1s period within 600 km of epicentre. M b =body-wave (similar to above) M s =surface wave (wave periods of 20s measured anywhere on globe M o =seismic moment M w = moment magnitude

9. The Richter scale Steps: 1. Measure the interval (in seconds) between the arrival of the first P and S waves. 2. Measure the amplitude of the largest S waves. 3. Use nomogram to estimate distance from earthquake (S-P interval) and magnitude (join points on S-P interval scale and S amplitude scale). 4. Use seismograms from at least three geographic locations to locate epicentre by triangulation.

10. The Richter scale nomogram Nomogram 1 2 3 Steps

11. Z Locating the epicentre: X, Y and Z are seismograph stations Y X 220 km epicentre 280 km 150 km

12. Earthquake magnitude: scales based on rupture dimensions (equivalent to energy released ) M o = seismic moment. = μ * A * d, where μ is the shear modulus of rock; A is the rupture area, and d is displacement M w = moment magnitude. = 2/3 * log M o - 10.7 N.B. moment scales do not saturate

13. Saturation of non-moment scales

14. Earthquake magnitude: scales based on shaking intensity e.g. Mercalli, Rossi-Forel, San Francisco scales MMI (=Modified Mercalli Index) I Not felt ….. VI Felt by all. Many frightened and run outdoors. Persons walk unsteadily. Pictures fall off walls. Furniture moved, trees shaken visibly. …. XII Damage nearly total. Objects thrown into air . Sichuan earthquake, May 12, 2008

15. Earthquake geography

16. Seismic hazards Locating faults Estimating recurrence: history and geology Measuring relative motions and crustal deformation Learning from analogies Assessing probabilities

17. Locating faults: Seattle Fault

18. San Francisco City Hall, 1906 Recurrence - historical records

19. Recurrence: geological evidence e.g. Pallett Creek, CA (after Sieh, et al. 1989)

20. Prediction: current crustal deformation

21. Prediction: crustal velocity (mm/yr) from repeated GPS measurements at permanent stations Why are all stations moving to NW?

22. Learning from analogues (Turkey - California)

23. The Bay Area: earthquake probabilities (AD2000-2030) N.B. A probability of 70% over 30 years is equivalent to a daily probability of 1 : 15 000

24. Probabilities, yes! but prediction, no! 1996 - Earthquake prediction group of Japanese Seismological Survey voluntarily disbands (after Kobe) 2000 - British researcher argues that prediction of main shock impossible at present; immediate goal should be prediction of aftershock location and magnitude

25. Individual seismic hazards Shaking = accelerated ground motion Liquefaction = failure of waterlogged sandy substrates Landslides, dam failures, etc. Tsunamis = seismic sea waves Fire, etc .

26. Predictions of shaking intensity on San Andreas fault (long segment) in the Bay Area Rupture

27. Shaking and liquefaction: the importance of surficial geology

28. Building collapse as a result of soil liquefaction, Niigata, Japan, 1964

29. Liquefaction and the urban fire hazard: San Francisco, 1906 2-6 m of lateral displacement in old marsh soils -> 300 breaks in water lines City lost 90% of water supply; fire s raged out of control Photos: Archives, Museum of San Francisco

30. Ground motion, structural damage and basin morphology: Mexico City, 1985 periodic periodic random body\surface surface/body Damage heavy light heavy ridge basin basin

31. Bedrock topography underlying Fraser delta

32. Earthquakes don’t kill; buildings do! Building harmonics Buildings at high risk URM = unreinforced masonry; open lower storeys; poor ties to foundations and between storeys; lack of cross-bracing; poor quality materials. Collapsed school building, Ying Xiu, Sichuan, China (May 12, 2008); >10,000 children died in this earthquake

33. The response of mud-brick buildings to ground shaking The 2 000-yr old citadel in Bam, Iran Pre-earthquake Post-earthquake (Dec. 2003)

34. “Much of the building is done by people putting up their own houses. But they cannot afford proper materials and do not use skilled labour. There are many small kilns producing bricks but because of demand these are not fired for the 28 days needed to make them strong.” Mohsen Aboutorabi, Professor of Architecture, (BBC News, 2003/12/30, discussing the Bam earthquake in which ~40,000 died) Muzaffarabad, Pakistan (October 8, 2005 M 7.7; depth 10km)

35. << << wall collapse, Pakistan, 2005 <<<< pancaking of ‘soft-storey’ buildings near Algiers (May, 2003); Complete collapse of multi-storey apartment, Pakistan, 2005 >>>>

36. Bridge collapse Loma Prieta earthquake, CA (1989)

37. Preparedness (examples) Buildings - site selection, design to code, retrofit, upgrade codes ; Strengthen bridges, dams, pipelines; Earthquake drills - houses, schools, search & rescue; Emergency planning - survival kits, evacuation routes, fire prevention, utility failures, communication alternatives, education

38. Preparedness: Modifying the building code in the western US 1969 1976 1988 1996 UBC = Uniform Building Code

39. Public education?

40. Post-earthquake adjustments Compare: abandonment of Antigua Guatemala (mid- C 18th) vs. reconstruction of Lisbon (post-1755), San Francisco (post-1906), Kobe (post-1995).

41. Cascadia: megaearthquakes at the plate boundary M w = 9.2?

42. 9.2 (1964) 9.3 (2005)

43. Earthquake sequences, Nankai Trough and Cascadia or here? S U W W? Y

44. The scientists Kenji Satake Alan Nelson Brian Atwater

45. Buried marsh soils as evidence for interplate earthquakes at Cascadia

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