2. Global seismicity
Earthquake epicenters (locations) are shown by the colored dots. Note locations
and concentrations of activity. Compare with volcano locations.

3. Plate collisions and volcanoes
Ocean-ocean
Ocean-continent
Continent-continent

4. India-Asia continent-continent collision

5. Rock Behavior How rocks respond to applied forces (stress)
Stress – force per unit area (lbs per sq in)
Response is termed “strain”
Elastic deformation (reversible)
Ductile deformation (flow)
Brittle deformation (fracture)

6. Rock breakage Fracture Fault Separation only; no vertical movement
Vertical and/or horizontal motion

7. Note offset in rocks

8. Footwall
block
Hanging wall
block

9. Note different fault motions
Normal or dip-slip
fault
Strike-slip fault
Reverse fault

10. Strike-slip motion on the plates

11. Note relative position of features

12. Subduction process Shallow-focus: 0 to 70 km depth
Intermediate-focus: 70 to 300 km depth
Deep-focus: 300 to about 700 km depth

13. P- and S-wave motion

14. Note changes in amplitude of the three wave arrivals

15. Seismogram of EQ near recording station

16. Selected seismic stations in the US

17. Earthquake magnitudes
Measures the “size” of an EQ
Four types of measurements
Local (ML) – original Richter scale
Body-wave (Mb) – P-wave amplitude
Surface-wave (Ms) – Rayleigh-wave amplitude
Moment (Mw) – considers amount of strain energy release along entire fault rupture.

18. Comparison of magnitude scales

19. The Big Ones
Japan Mar 2011
9.0

20. Intensity scale Measures damage caused by seismic energy
Established by Mercalli (Italian) in 1902; modified in 1931 to reflect enhanced building standards in US
Uses Roman numerals (I – XII)
Values depend on EQ magnitude, distance from source, bedrock type, building material and style, duration of shaking

21. Isoseismal map of Dec 1811 EQ near New Madrid, MO

22. Earthquakes don’t kill people- buildings do
Many deaths in older regions on Earth due to poor quality construction, especially through trans-Mediterranean/Asiatic belt
Secondary events (aftershocks) destroy already weakened structures
Surface waves produce the greatest damage

23. Benefits of EQs Changing natural resource paths Natural mitigation
Groundwater
Oil and natural gas
Exposures of minerals
Natural mitigation
Small events lessen likelihood of large events

24. Short-term predictions
Precursors
Events that imply an EQ; usually small magnitude events, often in swarms
Foreshock (sometimes) – main shock – aftershock
Ground deformation
Water level changes in wells
Seismic gaps
Greatest potential for large events in the gap

25. Sample seismogram showing P, S, and surface waves

27. Effects of EQs Shaking and ground rupture Liquefaction
Regional elevation changes
Landslides
Fires
Disease

28. Humans cause earthquakes by
Crustal loading by dams and reservoirs
Injection of liquid waste
Underground nuclear explosions

29. Human caused Eqs near Denver, CO

30. Earthquakes in the United States
Where do most EQs occur in US and why?
What’s happening in eastern & central US
Figure 5.1

31. Subduction zones in western North America
Alaska
Subduction of Pacific Plate
Pacific Northwest (BC-WA-OR-CA)
Subduction of Juan de Fuca Plate and smaller Gorda Plate
Cascadia Subduction Zone
Volcanoes on land
Figure 4.8

32. Subduction Zone Earthquakes
Largest EQs worldwide
9 of the 10 largest earthquakes ( ) were related to plate subduction
One in Tibet was due to India hitting Asia
These 9 occurred along Circum-Pacific “Ring of Fire”
Five EQs were located in northern Pacific [Japan-Kamchatka-Aleutians]

33. Examples of Subduction Zone Earthquakes
Chile 1960 (Mw = 9.5): Nazca Plate diving under South American Plate; tsunami producer
Alaska 1964 (Mw = 9.2): Pacific Plate dives beneath North American Plate; tsunami producer
Mexico 1985 (Ms = 8.1): Cocos Plate dives beneath North American Plate
Indonesia 2004 (Mw = 9.1): India Plate dives under Burma Plate; major tsunami producer
Japan 2011 (Mw = 9.0): Pacific Plate dives under North American Plate; major tsunami producer

34. Seismic Gap, Mexico, Sept 19,1985 Ms = 8.1
Mexico earthquake filled Michoacan seismic gap
Guerrero gap remains
Major aftershocks of Ms =7.5 and 7.3 within a month
See also Figure 4.4

35. Fig 2.20a

37. Average annual worldwide frequency of EQs magnitude 6.0 or greater
M 6.0 – 6.9 Strong
M 7.0 – 7.9 Major 15-20
M Great 1 every 2-3 years

38. San Andreas Fault System
Movement occurs on many faults
Displacement is distributed over a wide zone
Right-lateral strike-slip motion

39. San Andreas: Earthquake Probabilities
Probability of major earthquake ( )
Use historical and sag-pond data to calculate recurrence intervals Al

40. Loma Prieta, Oct 17,1989 [World Series EQ]
Magnitude 6.9; 67 killed
Epicenter at Loma Prieta, highest peak in Santa Cruz Mountains
100 km SSE of San Francisco
Section of San Andreas that moved in 1906 EQ ruptured again
Marina district in SFO was built on rubble from 1906 EQ; mud was pumped in to fill holes;
very unstable “land”
Game 3 halted by Commissioner; after 10-day recess, series continued in Oakland – Oakland swept series 4 games to 0.

42. Fig 2.18a

43. Seismic Wave Amplification near Oakland

46. Plate boundary is not a discrete line, but rather a zone the width of the Bay Area
Notice the many
major faults that
are parallel to
the San Andreas fault

47. Location of Hayward fault

48. Univ of California stadium in Berkeley
The trace of the Hayward fault runs through goal posts
Left side is moving N [top of image]

50. 30 yrs of
activity;
crosses are
epicenters

51. New Madrid, Missouri,
Series of three earthquakes in Mississippi River valley (Dec 1811-Feb 1812)
4 main events, 3 w/ magnitudes > 8.0 !
Knocked down chimneys 400 miles away!
Shook windows 800 miles away!
Neotectonic analysis indicates earlier EQs in 500, 900, 1300, 1600 AD  recurrence interval of years.
Why did it affect such a large area?

52. EQs associated with volcanoes
Those connected with active subduction such as western U.S.
Much larger magnitudes due to brittle rock
Isolated volcanism such as Hawaii
Usually lower magnitude due to molten rock

53. Foci of Hawaiian EQs