1. Earthquake: Vibration of Earth produced by the rapid release of elastic energy accumulated in rocks.

2. Earthquakes
Tectonic forces that move crustal blocks cause fractures in the lithosphere called faults.
Crustal blocks on either side of fault continue to move, resulting friction causes fault to “seize up”.
Elastic energy is stored in rocks adjacent to the jammed up fault, causing them to buckle and deform.
Finally, elastic energy accumulated in the rock exceeds the friction that holds rock along an existing fault line.

3. Earthquakes and Faults
The earthquake begins at the focus, which is the initial point of rupture along the fault, at depth.
The epicenter is the location on the earth’s surface directly above the focus.
Vibrational energy radiates from the focus in all directions, in the form of waves.
Scarp: vertical offset caused by faulting ( in this diagram it’s actually the mountain range).

4. Earthquake energy
Interior forces (convective flow) push tectonic plates.
at plate boundaries, frictional forces hold plates stationary. While rocks along plate boundary are “stuck”, elastic energy is stored and causes elastic deformation.

5. Energy release – Elastic rebound
Frictional resistance holding the rocks together is overcome.
Resulting movement releases stored energy as rocks return to original shape.

6. Energy Storage and Release
Released energy is in the form of waves, which cause movement on the earth’s surface and interior

7. Energy storage and release
Energy release may also result in open fissures (not the same as faults, but dangerous!

8. Seismology: Study of Wave Energy in the Earth
Seismic – relating to earthquakes or earth vibrations

9. Types of Seismic waves
Body waves travel entirely through earth’s interior
Primary (P) waves
Push-pull (compress and expand)
Travel through solids, liquids, and gases
Secondary (S) waves
Slower velocity than P waves
Slightly greater amplitude than P waves
Travel though solids only
Primary wave
Secondary Wave

10. Seismic Wave Motion
To view this animation, click “View” and then “Slide Show” on the top navigation bar.

11. Seismograph
Instrument used to record surface and body waves passing through the earth
More than one type of seismograph is needed to record both vertical and horizontal ground motion
Records obtained are called seismograms

12. Seismographs
To view this animation, click “View” and then “Slide Show” on the top navigation bar.

13. Figure 14.6

14. Figure 14.8

15. Figure 14.9

16. How Big
Modern measurement scales (Richter, moment magnitude) measure the amount of energy released by a quake.
This value is the same no matter how far away from the epicenter the measurement is taken

17. How Big
An earthquake occurs in Pakistan. Pakistanis report a magnitude of Scientists in California would probably measure a magnitude of:
Greater than 6.2
6.2
Less than 6.2

18. How Big
An earthquake occurs in Pakistan. Pakistanis report a magnitude of Scientists in California would probably measure a magnitude of:
Greater than 6.2
6.2 – correct!
Less than 6.2

19. Magnitude Scales
measure energy released (objective, rather than intensity (subjective)
Logarithmic – each number on the scale increases by a factor of 10, allows wider range

20. Table 14.2

21. Richter Magnitude (ML)
introduced by Richter and Gutenberg in 1935 for comparison of California earthquakes.
Based on the amplitude (height) of the largest seismic wave recorded during earthquake.
Accounts for the decrease in wave amplitude with increased distance from epicenter
Each unit corresponds to a tenfold increase in wave amplitude and a 32-fold energy increase
Originally for use in California only with a Wood-Anderson torsion seismograph only up to 6.5
Modern Richter Scales (Ms , Mb ) have been modified and work on all seismographs, measuring up to 8.

22. Figure 14.11

23. The table at the right is my original slide for the amount of energy released (in terms of TNT needed) for Richter Scale measurements. A metric ton = 1000 kg
This is before our text included fig (p. 345).
There is considerable disagreement!

24. Here is the source of the information in our text, look at the difference!

25. http://earthquake.usgs.gov/learn/faq/?faqID=33 4 0.22E+11 0.63E+11 15.
Magnitude
Es (from Me)
Es (from Ms or Mw)
Tons of TNT
Nuclear Bomb Equivalence (# of bombs) 4
0.22E+11
0.63E+11
15.
0.00 5
0.71E+12
0.20E+13
475.
0.02 6
0.22E+14
0.63E+14
15023.
0.79 7
0.71E+15
0.20E+16
25.0 8
0.22E+17
0.63E+17
790.6 9
0.71E+18
0.20E+19
25,003.3

26. Other sources http://www.themeter.net/sism_e.htm

27. Moment Magnitude (Mw)
developed because none of the “Richter-like” magnitude scales adequately estimates the size of very large earthquakes. Wave amplitude is limited on seismograph.
Derived from the amount of displacement that occurs along a fault
Gained wide acceptance
Measures very large earthquakes more accurately
Can be derived mathematically
Can be verified by field studies and seismographic methods

28. Map showing major tectonic boundaries and earthquake distribution (in yellow)
FIGURE 7.15 Earth’s major earthquake zones coincide with tectonic plate boundaries. Each yellow dot represents a moderate
or large earthquake that occurred between 1985 and 1995.

29. Circum-Pacific Belt aka Ring of Fire
Chapter 14, Figure 14.16

30. Table 14.3

31. Transform boundaries, e.g. San Andreas Fault Zone
Strike-slip fault; movement along fault is mainly horizontal
Fault creep – small, slow movements along fault
Stick-slip movement – fault moves in a series of jolts with no movement in between. Significant energy buildup possible, resulting in is large-magnitude damaging earthquake

32. Earthquakes and plate boundaries
Convergent boundaries – one plate sliding under another
Benioff zone – upper part of sinking plate, where it scrapes past opposing plate, causing earthquake activity along the down-plunging contact zone.

33. subducting plate, called the Benioff zone.
FIGURE 7.20 A descending lithospheric plate generates magma and earthquakes in a subduction zone. Earthquake foci, shown by stars, concentrate along the upper portion of the
subducting plate, called the Benioff zone.
Fig. 7.20, p.165

34. Earthquakes along divergent boundaries
Friction along sliding blocks (transform faults)

35. Earthquakes in plate interiors
, New Madrid, MO, site of aborted divergent boundary
This area is still seeing active movement along the fault.

36. Tsunami
When an earthquake occurs beneath the sea, the sea floor rises and falls, due to rupture and elastic rebound.
Resulting water displacement forms a fast-moving wave.
In the deep water of the open ocean, tsunami are barely detectable.
In shallow water near shore, the wave speed decreases as it drags against the bottom.
The water “stacks up”, causing a large wall of water to make landfall.

37. December 2004 Sumatra-Andaman Tsunami
This shows a portion of the convergent boundary between the Eurasian plate and the Indo-Australian plate. The latter is moving northward, pushing against the former
Green star shows epicenter of earthquake that caused tsunami.
Red arrows show plate motion
Red dots show earthquakes > magnitude 5.0, from 1965 to 2004.

38. Chapter 14 Opening Figure

39. Tsunami – deep and shallow water

40. Tsunami
To view this animation, click “View” and then “Slide Show” on the top navigation bar.

41. Tsunami advancing after initial retreat

42. Tsunami Travel Times to Hawaii

43. Laguna Salada Earthquake April 4, 2010
ftp://hazards.cr.usgs.gov/maps/sigeqs/ / jpg
This site has some good information about the recent “Easter Quake” near Mexicali. Click on any part of the site to enlarge it

44. Haiti Earthquake – Jan 2010

45. Magnitude 7.0
Energy released is equal to approximately 32 Megatons TNT
Why do earthquakes happen in Haiti?
The answer is Plate Tectonics!

46. Plate Tectonic Map

47. A close up showing the Caribbean Plate; it’s northern boundary runs through Haiti

48. the Caribbean Plate moves eastward while the North American Plate moves westward. The yellow lines are faults which define a small microplate:

49. The red dots show historic earthquake activity
The red dots show historic earthquake activity. The plates try to move past each other and get stuck, building up a lot of energy in the process

50. The energy release when the plate gets “unstuck” causes the earthquake and resultant damage

51. December 2004 Sumatra-Andaman Tsunami
This shows a portion of the convergent boundary between the Eurasian plate and the Indo-Australian plate. The latter is moving northward, pushing against the former
Green star shows epicenter of earthquake that caused tsunami.
Red arrows show plate motion
Red dots show earthquakes > magnitude 5.0, from 1965 to 2004.

52. Plate tectonics of Southeast Asia
Much of Indonesia is actually located on a separate plate called the Sunda Plate (“Sonde” here).
The Sunda plate is bounded on the north by the Burma Microplate (“Birmanie”), site of the 2004 quake/tsunami.
Note the large subduction zone, as the Australian plate pushes underneath these plates.
Several microplates bound the the Sunda on the SE corner

53. Plate tectonics of Southeast Asia
Here is another view of the Sunda Plate. The yellow line is a fault zone which has been ruptured by large earthquakes in the last decade

54. Plate tectonics of Southeast Asia
This shows the sliver of Sunda Plate between the subduction zone and the Sumatran Fault, which is a right lateral transform fault, similar to the San Andreas.

55. Ercis Earthquake, October 2011

56. Anatolian Plate and Bitlis-Zagros Thrust, showing Van Lake, Epicenter Location
Anatolian microplate is squeezed in between Arabian, Eurasian and African plates.
This area is part of the Alpine-Himalayan Belt

57. Earthquake Activity in Turkey
Along the North Anatolian Fault, a transform fault boundary much like the San Andreas Fault
At the Bitlis-Zagros Thrust Zone, where the Arabian Plate and Anatolian Plate experience continental collision.
Note location of Van Lake, epicenter of most recent earthquake, just north of the collision zone.

58. Comparison of Ercis quake (2011) earthquake with Izmit quake (1999)

59. Comparison of San Andreas and North Anatolian Faults

60. USGS Site