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Earthquakes
- Under Construction
Plate
Tectonics, the Cause of Earthquakes. The plates consist of an outer
layer of the Earth, the lithosphere, which is cool enough to behave as a
more or less rigid shell. Occasionally the hot asthenosphere of the Earth
finds a weak place in the lithosphere to rise buoyantly as a plume, or hotspot.
The satellite image below shows the volcanic islands of the Galapagos hotspot.
Understanding
Earthquakes
Comparison of Magnitude and Destructive
Power Earthquakes are measured in two different
ways. The most scientific measure is the Richter scale which tells us an
earthquake's magnitude or how much energy was released by the fault movement.
For each earthquake there is only one magnitude or Richter measurement.
The energies associated with
earthquakes of various magnitudes, and of a number of earthquakes and other
phenomena. The larger unit of energy for earthquakes is equated to , the yield of
TNT. The table was borrowed from GEOLOGY:
PRINCIPLES AND APPLICATIONS taught by Dr. J Louie at the University of
Nevada at Reno.
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Richter
Magnitude |
TNT for Seismic
Energy Yield |
Example (approximate) |
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-1.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
6.5
7.0
7.5
8.0
8.5
9.0
10.0
12.0
. |
|
|
6
30
320
1
4.6
29
73
1,000
5,100
32,000
80,000
1 million
5 million
32 million
160 million
1 billion
5 billion
32 billion
1 trillion
160 trillion
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ounces
pounds
pounds
ton
tons
tons
tons
tons
tons
tons
tons
tons
tons
tons
tons
tons
tons
tons
tons
tons
. |
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Breaking a rock on a laboratory table
Large blast at a construction site
.
Large Quarry or Mine Blast
.
.
.
Small Nuclear Weapon
Average Tornado (total energy)
Little Skull Mtn., NV Quake, 1992
Double Spring Flat, NV Quake, 1994
Northridge, CA Quake, 1994
Largest Thermonuclear Weapon
Landers, CA Quake, 1992
San Francisco, CA Quake, 1906
Anchorage, AK Quake, 1964
Chilean Quake, 1960
(San-Andreas type fault circling Earth)
(Fault Earth in half through center, or earth's daily receipt of
solar energy. |
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The yield of Little Boy, the atomic bomb that
was dropped on Hiroshima at the end of WW2, was 15,000 tons (of TNT). One ton of
TNT releases 63,100,000 joules of energy. Compare the destructive energy of the
earthquake you have studied to that of Little Boy. How many of these bombs would
it take to equal the energy released?
World Map
of recent earthquakes and volcanoes
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