1. Intraplate Earthquakes
New Madrid, Missouri: December 1811, January 1812, February 1812
Figure 3-17

2. Intraplate Earthquakes
Eastern U.S. earthquakes less frequent, but more widely felt
Crust is older and transmits stress
Figure 3-20

3. Earthquake Size and Characteristics
How big is it?
Answer in terms of perceived effects: intensity
Answer in terms of amount of energy released: magnitude

4. Earthquake Intensity Mercalli Intensity Scale developed in 1902
Based on effects
Local small quake is similar to distant large quake
Table 3.2

5. Felt effects using Mercalli Scale

6. Felt effects using Mercalli Scale
Hypothetical M7.8 earthquake

7. Landers 1992 earthquake:
Felt intensity by zip code

8. Earthquake Magnitude
Richter Magnitude Scale (ML) derived by Charles Richter in 1935
Uses maximum amplitude of earthquake waves on seismograph
Logarithmic scale
Richter magnitude less accurate above M6.5
Figure 3-29

9. Problems with scales
Moment magnitude is measure of total energy expended during earthquake
Determined from long-period waves
Moment = (shear strength of rocks) x (surface area of rupture) x (slip distance on fault)
Each number is 32X energy
Each 2 numbers =1000X
This is the most common scale for quakes >3.5

10. Another example of M=1/f

11. 1995
Kobe earthquake,
Japan

12. 1989
Loma Prieta
earthquake,
SF Bay Area

13. Liquifaction
Water in sediment causes solid rock to behave like a liquid.

14. Liquifaction

15. Secondary Ground Effects
Surface rupture-scarp
Earthquakes often trigger landslides
Can also cause liquefaction
Soils become almost liquid when shaken, solidify when shaking stops
Significant damage to structures atop liquefied sediments
Fires

17. Surface rupture-scarp

18. 1906 earthquake surface rupture. 8’ fence offset above
And

20. Australia, 1968, M6.8

21. Armenia, 1988, M6.9

22. Borah Peak, ID: 1983 M7.3

23. California, 1979, M6.9

24. Landslides caused by 2002 Denali Fault earthquake

25. 1965 Seattle quake M6.5

26. Liquifaction
Water in sediment causes solid rock to behave like a liquid.

27. This residential and commercial building sank more than three feet into the partially liquefied soil.

28. Liquifaction: Niigata, Japan, 1964

29. San Francisco 1906 M8.3
Secondary effects: Fire

30. Long term probability
Probability of where and when an earthquake will strike used to construct risk map
Figure 4-14

31. Earthquake Hazards 2% chance in next 50 years

32. The San Francisco Bay Area
Figure 4-17

33. Las Cruces:
15-18%
chance
of M5 in
50 yrs.

34. Sample Test Questions