Geology Reference
In-Depth Information
TABLE 8.1
Some Signifi cant Earthquakes
Magnitude
(estimated before 1935)
Deaths
(estimated)
Year
Location
1556
China (Shanxi Province)
8.0
1,000,000
1755
Portugal (Lisbon)
8.6
70,000
1906
USA (San Francisco, California)
8.3
3000
1923
Japan (Tokyo)
8.3
143,000
1960
Chile
9.5
5700
1964
USA (Anchorage, Alaska)
8.6
131
1976
China (Tangshan)
8.0
242,000
1985
Mexico (Mexico City)
8.1
9500
1988
Armenia
6.9
25,000
1990
Iran
7.3
50,000
1993
India
6.4
30,000
1995
Japan (Kobe)
7.2
6000+
1998
Afghanistan
6.9
5000+
1999
Turkey
7.4
17,000
2001
India
7.9
14,000+
2003
Iran
6.6
43,000
2004
Indonesia
9.0
>220,000
2005
Pakistan
7.6
>86,000
2006
Indonesia
6.3
>6200
◗
Figure 8.1
The Elastic Rebound Theory
Fault
Fence
Original position
Deformation
Rupture and release of energy
Rocks rebound to original undeformed shape
According to the elastic rebound theory, rocks experiencing defomation store
energy and bend. When the initial strength of the rocks is exceeded, they rupture,
releasing their accumulated energy, and “snap back” or rebound to their former
undeformed shape. This sudden release of energy is what causes an earthquake.
During the 1906 San Francisco earthquake,
this fence in Marin County was displaced by
2.5 m. Whereas many people would see a
broken fence, a geologist sees that the fence
has moved or been displaced and would look
for evidence of a fault. A geologist would also
notice that the ground has been displaced
toward the right side, relative to his or her view.
Regardless of what side of the fence you stand
on, you must look to the right to see the other
part of the fence. Try it!
a
b
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