2. A fracture (crack) in the earth, where the two sides move past each other and the
relative motion is parallel to the fracture.
90˚ dip = vertical fault plane
0˚ strike = north parallel fault plane
Fault
2
Source: wikipedia
12. Faults and Plate Boundaries
Normal faults are associated with divergent plate boundaries
Animation of divergent boundary
12
Source: USGS public domain
13. Faults and Plate Boundaries
Reverse faults are associated with convergent plate boundaries
Animation of convergent boundary
13
Source: USGS public domain
14. Faults and Plate Boundaries
Strike-slip faults are associated with transform plate boundaries
Animation of transform boundary
14
Source: USGS public domain
16. After the great 1906 San Francisco
earthquake, Harry Fielding Reid
examined the displacement of the
ground surface around the San
Andreas Fault. From his observations
he concluded that the earthquake
must have been the result of the
elastic rebound of previously stored
elastic strain energy in the rocks on
either side of the fault. In an
interseismic period, the Earth's
plates move relative to each other
except at most plate boundaries
where they are locked.
Elastic Rebound Theory
16
17. After the great 1906 San Francisco
earthquake, Harry Fielding Reid
examined the displacement of the
ground surface around the San
Andreas Fault. From his observations
he concluded that the earthquake
must have been the result of the
elastic rebound of previously stored
elastic strain energy in the rocks on
either side of the fault. In an
interseismic period, the Earth's
plates move relative to each other
except at most plate boundaries
where they are locked.
Elastic Rebound Theory
17
Source: google images
18. Elastic Rebound Theory
The elastic rebound theory explains how energy is spread
during earthquakes. As plates on opposite sides of a fault are
subjected to force and shift, they accumulate energy and
slowly deform. When the stresses exceed the internal
strength of the rock, a sudden movement occurs along the
fault, releasing the accumulated energy, and the rocks snap
back to their original undeformed shape.
This theory was discovered by making measurements at a
number of points across a fault. Prior to an earthquake it was
noted that the rocks adjacent to the fault were bending. These
bends disappeared after an earthquake suggesting that the
energy stored in bending the rocks was suddenly released
during the earthquake.
18
19. Elastic Rebound Theory
Original alignment
of points
Alignment of points
after accumulation of
elastic strain
Final alignment of
points
Fault
19
20. Elastic Rebound
The animated picture shows a road, a fence, and a line of trees crossing a
fault. As the rocks adjacent to the fault are deformed, stresses build up in
rock, rupture occurs when the shearing stresses induced in the rocks
exceed the shear strength of the rock, followed by sudden slip, releasing
energy that causes destruction. 20
25. Sequence of Elastic Rebound
Tectonic plates move relative to each other
Elastic strain energy builds up in the rocks along fault planes
Since fault planes are not usually smooth, great amounts of
energy can be stored (if the rock is strong enough) as
movement is restricted due to interlock along the fault.
Stresses (force/area) are applied to a fault.
Strain (deformation) accumulates in the vicinity of friction-
locked faults.
When the shearing stresses induced in the rocks on the fault
planes exceed the shear strength of the rock, rupture occurs.
Rupture continues over some portion of the fault. Slip is the
distance of displacement along a fault.
25
26. Rock Deformation and Earthquakes
Earthquakes result from motion along faults
Earthquakes represent the brittle failure of rock and hence
they occur in upper crust, where the temperature and
pressure are relatively low.
Not all motions on faults produce earthquakes. Rocks may
also creep if the faults are too weak to store up the energy of
prolonged stress.
Elastic rebound theory explains deformation before and
during earthquakes as brittle failure following the
accumulation of elastic strain.
26
27. Kramer (1996) Geotechnical Earthquake Engineering, Prentice Hall.
Udias, A. (1999): Principles of Seismology, Cambridge University Press,
Cambridge.
Shearer, P. M. (1999): Introduction to Seismology, Cambridge University Press,
Cambridge.
Ben Menahem, A. and Singh, S. J. (1980): Seismic Waves and Sources,
Springer-Verlag, New York.
Cox, A. and Hart, R.B. (1986): Plate Tectonics - How it Works, Palo Alto,
California, Blackwell Scientific Publications, 392 p.
http://pubs.usgs.gov/gip/dynamic/dynamic.html (Accessed on 25 September 2012)
References
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