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This web site is a simple guide to making
your own seismometer. As an eathquake happens you will be able to see the movement of the earth using a simple setup. Included is
some background information on earthquakes, prediction and prevention, and lots of pictures to look at, without all the jargon that
usually confuses us!!
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The Earthquake 1970
- Anon.
Effect
Reference:
What does a seismometer do?
What is a galvanometer?
Why would you use a galvanometer to make a seismometer?
What does this seismometer actually measure?
Most of us know that when lightning strikes, you can count the time between the lightning and the thunder, and that is the number of
kilometers away the storm is. Well, the same works with earthquakes. You can count the time between the first shake (primary
wave) and the second jolt (secondary wave) and times that number by eight. Then you have a rough guess at how far away the
earthquake began. That is, if you have time while running under a door or struggling under a table of course!!
Using a simple physics formula d = vt you can put in the distance and the time taken, to find the velocity that the waves travel
through the surface. Once you have found this velocity, try it again perhaps with the experiment set up on grass or sand instead of
a desk for example. As long as it is a continuous flat surface you will be able to work out the velocity.
Another exciting thing you can do with your seismometer is connect it up to an analogue to digital converter. From this you can
record and print out the simulated waves and compare them to natural earthquakes. What more could you want!!
What pow'rful hand with force unknown
Can these repeated tremblings make?
Or do the imprison'd vapours groan?
Or do the shores with fables Tridents shake?
Ah no! The tread of impious feet,
The conscious earth impatient bears;
And shudd'ring with the guilty weight,
One common grave for her bad race prepares.
Intensity
Only felt by a very few.
Felt by persons at rest.
Felt indoors. Some hanging objets swing.
Vibration like heavy traffic passing or like the jolt of a heavy object falling.
Generally felt outside. Most sleepers awakened. Small unstable objects
move. Some glassware and crockery broken.
Felt by all. Difficulty in walking steadily. Objects fall from shelves. Slight damage to badly constructed buildings.
General alarm. Difficulty in walking steadily. Some danger to buildings not designed to withstand earthquakes. Furniture moves. Unreinforced chimneys, roofing tiles and water tanks broken.
Alarm may approach panic. Steering of motorcars greatly affected. Some
damage to earthquake resistant building types. Monuments and elevated tanks brought down.
Heavy damage to building and bridges. Houses not secured to foundations shifted off. Landslides widespread on steep slopes. Cracking of ground conspicuous.
Severe damage to many buildings and bridges even those of most recent design.
Few if any structures remain standing. Earth slumps and land slides in
soft ground. Rails bend greatly.
Damage total. Waves seen on ground surface. Objects thrown into the
air.
Why would you want to make a seismometer?
People can study earthquakes by looking at ones that have already happened and have been recorded by seismographs. Perhaps in
the
future we will be able to predict when earthquakes will happen and this may be able to save lives or prevent people from getting
hurt. It may also take some of the terror of the
unknown away from earthquakes.
A seismometer basically tells us how much the ground moved during an earthquake.
When we hear that it was a 'magnitude 4.8' earthquake, it is a seismometer that has
told us that. Seismometers are very useful in telling us how big earthquakes are and how often they happen. When an earthquake
happens, waves are made. A seismograph can pick up these waves and record them for us. If more than one seismometer picks the waves
up researchers can also tell us where the earthquake happened and how deep it was. These are important details for scientists who
are studying earthquakes, the same scientists that one day might be able to predict earthquakes for us!
A galvanometer sounds like a very technical piece of equipment, but it is quite easy to use. When there is an 'electric current' near, the galvanometer will pick it up. This makes the needle 'deflect' or move as we see it. The stronger the current, the further the needle moves.
A galvanometer can work similarly to a seismometer. First of all you have to place the galvanometer on its side, which changes the
way it works! This means that everything inside it works backwards and the
needle of the galvanometer moves when the surface under the galvanomter moves.
The surface can be a desk, grass, sand,
the floor or any other flat surface.
It measures the waves that arrive first. They are called the primary waves. They arrive first because they are the fastest. They are
also the ones that the galvanometer on its side can measure. They do not do the most damage - the secondary waves do that - but they
can rattle and shake windows. The secondary waves are the ones which move us up and down and side to side.
All you have to do is follow these simple steps and you will have your own working model of a seismometer.
Now you have your own seismometer!! Earthquakes can be made artificially by certain movements of the surface that the seismometer is
on. Some of these, however, will be too low or high in frequency for the galvanometer to pick up. Try it!!
One experiment that can be done is to connect two galvanometers (used as seismometers, i.e. on their side) up to oscilloscopes that
(preferably) have memories. Place the two galvanometers as far apart as you can on a continuous, flat surface. Measure the
distance between them. One person simulates a wave beside galvanometer one and another person waits at galvanometer two. When the
wave arrives at galvanometer two, record the time that it took to get there.
