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Let's first look at the structure of the earth. Earth is made
of rock that is very thick. It's divided into 3 main sections:
crust, mantle,
core. This Animation
from WNET and PBSonline, The Savage Earth, will show you these
layers.
Huge
sections of the crust, called plates,
are always moving, some floating like huge rafts on the almost-liquid
rocks below! When this happens, under great pressure and heat,
the rock in some places becomes squeezed, stretched, or folded
and can break.
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Where
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Earthquakes
can happen in many places, but there are some areas where they are
concentrated. They occur at or close to the edges of the major plates.
This area is called the Ring
of Fire. The epicenter
of an earthquake is the place on the Earth's surface directly above
the focus (more
than one are called foci) which is the place inside the Earth where
the quake originates. Foci are usually somewhere between the surface
and 100 km in depth. Find where the latest
earthquakes have been in the United States and in the World.
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Measuring
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Seismology
is the study of earthquakes and a seismologist is the scientist
that studies earthquakes.
Measuring
Earthquakes
A seismograph is the instrument
used to measure earthquake shocks. It can record tiny earth tremors
thousands of miles away. Hundreds of seismograph stations are
located all over the world. Seismographs can be used to
find an earthquake's epicenter,
and its focus
underground. They record "P" waves
and "S" waves.
Geologists
use two different scales to measure how strong an earthquake is. The
Richter Scale measures magnitude,
the amount of energy released by an earthquake by measuring how
big a shock wave is. Each number on the scale is 10 times more
powerful than the number below it. A magnitude 3 earthquake is
ten times greater that a magnitude 2 and is easily felt. An earthquake
that registers 6 or more is considered a major quake.
The
Mercalli Intensity Scale measures the amount and type
of damage caused by the earthquake. Usually the intensity is greater
near the center of the quake.
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History
of Seismology
An
early
seismograph
Map
of world Seismograph Stations
Something
about waves.
P
waves
and S waves
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Facts
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Did
you know that there are earthquakes on the moon? They're called
"Moonquakes."Get more facts from the USGS Earthquake
Hazards Program. |
FAQ's
about Earthquakes |
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Myths
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Humans
developed many explanations for earthquakes before they had the
understanding and instruments to study them scientifically. You
can read about some of these ideas at Earthquake
Myths and Folklore, from the University of Memphis.
Here's a myth from Mongolia, China.
A gigantic frog which carried the world on its back, twitched periodically,
producing slight quakes. |
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Dangers
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Earthquake shaking can cause much
destruction and loss of life. The ground under buildings
can become loose and buildings can fall or sink. Rockslides can
occur. Liquefaction,
ground displacement, flooding, tsunamis,
and fire are all hazards
of earthquakes.
One of the dangers are tsunamis.
In the ocean tsunamis may be only 1m (3 ft) high and can be 90 miles
apart. They can travel at 500 mph. When they reach shallow coastal
waters they can grow to 35m (115 ft) high and cause massive flooding! |
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Predicting
and Preparing
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You
can't predict
earthquakes yet, nor prevent them, but you can protect yourself
by preparing
for one. One way scientists help is by comparing readings from
widely spaced seismographic stations to determine the exact position
of the earthquake's origin. This can help to warn of tsunami in
the Pacific Ocean.
What
to do before during and after an Earthquake
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Earthquakes
in Idaho
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The
Idaho
Geological Survey provides a history of earthquakes in Idaho.
Did you know that Idaho ranks fifth in the nation for earthquake
hazard, behind California, Nevada, Utah, and Alaska? The two largest
earthquakes in the lower 48 states in the last 45 years have been
in Idaho (1959 and 1983). Both caused fatalities and damage. Read
about them at: http://www.idahogeology.org/Services/GeologicHazards/Earthquakes/default.htm
To
see the most recent earthquake activity around Idaho visit: http://www2.state.id.us/bdsmitigation/earthquake/recent.htm
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This
Franklin Institute Website,
Earthforce, will lead you to much more information about
earthquakes.
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Once every 30 seconds somewhere in the world the ground shakes. The
shaking is called an, "
