The document provides an overview of earthquakes, including definitions of key terms such as amplitude, epicenter, hypocenter, and magnitude. It explains how to read a seismogram, calculate earthquake magnitude using the Richter scale, and locate the epicenter using triangulation from multiple seismograms. Additionally, it illustrates the energy release associated with different magnitudes and emphasizes the predominance of small earthquakes that go unnoticed by most people.

1. Week 2 Project
Gib Lucas
EDU 653
Dr. Merrill
6/28/2012

2. Earthquakes
Earthquake – Sudden slip on a fault, and resulting
ground shaking and radiated seismic energy caused by
the slip, or by volcanic or magmatic activity, or other
sudden stress changes in the earth.

3. Earthquake Terms
Amplitude – The size of the wiggles on an earthquake recording.
Epicenter – The point on the earth’s surface vertically above the (hypocenter ) focus,
point in the crust where a seismic rupture begins.

4. Earthquake Terms
Hypocenter – The point within the earth where an earthquake rupture starts.
The epicenter is the point directly above it at the surface of the earth. Also
commonly termed the focus.

5. Earthquake Terms
Magnitude – A number that characterizes the relative size of an earthquake.
Magnitude is based on measurement of the maximum motion recorded by a
seismograph.
P wave, or compression wave, is a seismic body wave that shakes the ground
back and forth in the same direction and the opposite direction as the direction
the wave is moving.
S wave, or shear wave, is a seismic body wave that shakes the ground back and
forth perpendicular to the direction the wave is moving

6. Earthquake Terms
Seismogram – A record written by a seismograph in response to ground motions
produced by an earthquake, explosion, or other ground-motion sources.

7. Earthquake Terms
The Richter magnitude scale was developed in 1935 by Charles F. Richter of the
California Institute of Technology as a mathematical device to compare the size of
earthquakes. On the Richter Scale, magnitude is expressed in whole numbers and
decimal fractions. For example, a magnitude 5.3 might be computed for a moderate
earthquake, and a strong earthquake might be rated as magnitude 6.3. As an estimate
of energy, each whole number step in the magnitude scale corresponds to the release of
about 31 times more energy than the amount associated with the preceding whole
number value.

8. OBJECTIVES
Reading a Seismogram
Calculating the Magnitude of an Earthquake
Finding the Epicenter of an Earthquake

9. How Are Earthquake Magnitudes
Measured?
The magnitude of most earthquakes is measured on
.the Richter scale, invented by Charles F. Richter in
1934.
For each whole number you go up on the Richter
scale, the amplitude of the ground motion recorded
by a seismograph goes up ten times.
CHARLES RICHTER STUDYING A Using this scale, a magnitude 5 earthquake would
SEISMOGRAM
result in ten times the level of ground shaking as a
magnitude 4 earthquake (and 32 times as much
energy would be released).

10. Earthquake Energy Release
To give you an idea how these numbers can add
up, think of it in terms of the energy released
by explosives:
A magnitude 1 seismic wave releases as much
energy as blowing up 6 ounces of TNT.
A magnitude 8 earthquake releases as much
energy as detonating 6 million tons of TNT.
Pretty impressive, huh? Fortunately, most of
the earthquakes that occur each year are
magnitude 2.5 or less, too small to be felt by
most people.

11. A TYPICAL SEISMOGRAM
When you look at a seismogram, there will be wiggly lines all
across it. These are all the seismic waves that the seismograph has
recorded.
Most of these waves were so small that nobody felt them. They
can be caused by heavy traffic near the seismograph, waves hitting
a beach, the wind, and any number of other ordinary things that
cause some shaking of the seismograph.
There may also be some little dots or marks evenly spaced along
the paper. These are marks for every minute that the drum of the
seismograph has been turning.

12. What do the Wiggles mean?
When you look at a seismogram, there will be wiggly lines all across it.
So which wiggles are the earthquake?
The P wave will be the first wiggle that is bigger than the rest of the little
ones . Because P waves are the fastest seismic waves, they will usually be
the first ones that your seismograph records.
The next set of seismic waves on your seismogram will be the S waves.
These are usually bigger than the P waves.

13. USE THE AMPLITUDE TO DERIVE THE MAGNITUDE OF THE EARTHQUAKE AND THE
DISTANCE FROM THE EARTHQUAKE TO THE STATION.
To find the magnitude:
1. Measure the distance
between the 1st P wave and
1st S wave (24 seconds).
2. Find the point for 24 secs.
On the chart and mark the
spot. The Epicenter is 215
kilometers away.
3. Measure the amplitude
(height) of the strongest
wave (23 mm).
4. Using a strait edge, draw a
line between the 2 marks
you made. The point where
your line crosses the middle
line on the chart is the
magnitude (strength) of the
earthquake. In this example
the earthquake had a
magnitude of 5.0

14. How Do I Locate That Earthquake's
Epicenter?
You have figured out how far your seismograph is from the epicenter and how strong the
earthquake was, but you still don’t know where the earthquake occurred.
To figure out just where that earthquake happened, you need to look at your seismogram and you
need to have seismograms from at least two other seismographs recorded for the same
earthquake.
For our example we will use seismograms from Detroit, Minneapolis, and Charleston.
You will also need a U.S. map, a ruler, a pencil, and a compass for drawing circles on the map.

15. FINDING THE EPICENTER
1. Check the scale on your map.
2. If 1 cm = 100 km, then an epicenter
of 215 kilometers away = 2.15 cm on map
3. Use the compass to draw a circle with a radius of the
number
From step 2 (radius is the distance from the center of
the circle to its edge. The center of the circle will be
location of your seismograph.
4. Do the same thing for the other seismograms. The
point where all of the circles overlap is the epicenter
of the earthquake.
THE POINT WHERE THE THREE CIRCLES INTERSECT IS THE EPICENTER OF
THE EARTHQUAKE.
THIS TECHNIQUE IS CALLED 'TRIANGULATION.'

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17. Sources
Bolt, Bruce A. Earthquakes: A Primer. San
Francisco: W.H. Freeman, 1978. Print.
©2007 MICHIGAN TECHNOLOGICAL
UNIVERSITY. PERMISSION GRANTED FOR
REPRODUCTION FOR NON-COMMERCIAL USES.
http://www.geo.mtu.edu/UPSeis/index.htm
http://earthquake.usgs.gov/learn/glossary/?te
rm=epicenter