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

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

3. North American tectonic regimes
(much simplified)

4. Styles of faulting

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

6. Seismic wave forms S wave P wave L wave L wave (Rayleigh wave)
(Love wave)

7. Earthquake magnitude: scales based on seismograms
ML=local (e.g. Richter scale) - based on amplitude of waves with 1s period within 600 km of epicentre.
Mb=body-wave (similar to above)
Ms=surface wave (wave periods of 20s measured anywhere on globe
Mo=seismic moment
Mw= moment magnitude

8. 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.

9. The Richter scale nomogram2 1
Steps 3
Nomogram

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

11. Earthquake magnitude: scales based on rupture dimensions (equivalent to energy released )
Mo= seismic moment. = m * A * d, where m is the shear modulus of rock; A is the rupture area, and d is displacement
Mw= moment magnitude. = 2/3 * log Mo
N.B. moment scales do not saturate

12. Saturation of non-moment scales

13. 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

14. Earthquake geography
Source: GSHAP, Switzerland

15. Seismic hazard: North & Central America

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 (LIDAR image)

18. Prediction: where will the next earthquake in the Bay Area occur?
Berkeley
San Andreas
Oakland
Hayward
San Francisco
San Jose
Santa Cruz

19. The Hayward fault runs through UC Berkeley campus (US $1 billion seismic upgrade program)
Lawrence
Livermore
UC Berkeley

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

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

22. Prediction: current crustal deformation

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

24. Learning from analogues (Turkey - California)

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

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

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

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

29. Shaking and liquefaction: the importance of surficial geology

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

31. 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; fires raged out
of control
Photos: Archives, Museum of San Francisco

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

33. Bedrock topography underlying Fraser delta

34. 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

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

37. Muzaffarabad, Pakistan (October 8, 2005 M 7.7; depth 10km)
“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)

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

39. Bridge collapse Loma Prieta earthquake, CA (1989)
Bay area Bridge

40. 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

41. Preparedness: Modifying the building code in the western US
UBC = Uniform Building Code

42. Public education?

43. Post-earthquake adjustments
Compare:
abandonment of Antigua Guatemala (mid-C18th) vs.
reconstruction of Lisbon (post-1755), San Francisco (post-1906), Kobe (post-1995).

44. Cascadia: megaearthquakes at the plate boundary
Mw = 9.2?

45. 9.2 (1964)
9.3
(2005)

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

47. The scientists Kenji Satake Alan Nelson Brian Atwater

48. Y U W S
Buried marsh soils as evidence for
interplate earthquakes at Cascadia