Earthquake Simulation
Objective:
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To compare the relative frequencies of slip size with real
earthquake data.
To observe force build up, slippage and release over
several slip cycles.
To compare the simulation results with the pattern of
stress build-up and release in different earthquake
models.
To investigate the concept of return times and stress
transfer in earthquake prediction.
To use a vibration detector to analyse the shock waves
given off by various size earthquakes.
This experiment uses a brick pulled along a surface covered in
sandpaper to model the behaviour of an earthquake. Turning a
pulley to build up tension in the string is like the build up of
stresses at a fault, and the brick movement over the sandpaper
is like the slippage that happens in an earthquake. You can
compare your results with real earthquake data and evaluate
the brick and sandpaper as an earthquake model. Watch this
video from Ross Stein (Science of Predicting Earthquakes), who
devised this experiment, to see how to set it up.
Equipment:
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Pulley for earthquake simulation
A plank or bench
A brick
Coarse sandpaper, plus adhesive tape or G-clamps to
stick it onto the plank or bench
A force meter (e.g. 0-20 N or 0-50 N)
Mete rule or tape measure with mm markings
Blu-Tack or double-sided tape to stick the ruler down
Straw pointer, plus something to stick it onto the brick
Graph paper
Eye protection
Vibration detector
Method:
1. Make sure the pulley is clamped onto the plank or bench and attach the string from the pulley
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onto the force meter.
Use another string attached to the force meter to tie around the brick.
Stick or tape a ruler with a millimetre scale onto the plank and a pointer onto the brick: you
should be able to measure the position of the brick against the scale to the nearest mm.
Place the brick at the end of the sandpaper furthest away from the pulley: make sure it is
completely on the sandpaper.
Wearing eye protection turn the pulley so it gradually increases the tension in the string (and
the force on the brick) until the brick starts to move. Increase the tension slowly so that it takes
several seconds before the brick slips.
Try this a few times. Watch what happens to the force meter reading: does the brick always
begin to slip when the force reaches the same value?
Place the brick back at the start position. This time, measure how far the brick moves each time
it slips. Record your results in a spreadsheet.
Continue until you have at least thirty readings.
9. Plot a histogram to show the frequency for each size of slippage.
10. What do you notice about the relative frequency of large slippages?
11. Compare your histogram with a histogram showing the frequency of different magnitudes of
earthquake.
This arrangement with a force meter provides a steady increase in tension in the string, equivalent to
stress building up in a seismic fault. The area of the brick in contact with the plank or bench represents
the fault and is constant in size. You may need to experiment with different combinations of brick and
sandpaper to get the best effect: the brick shouldn't move as soon as you start to turn the pulley but
should "go" suddenly. You may prefer to use sandpaper on the bottom of the brick too, and to use a
bungee cord in place of the string attached to the brick.
Seismometers detect the vibrations produced by earthquakes. If the ground moves underneath a mass
that is not fixed, the mass will tend to stay where it is and let the ground move underneath it;
seismometers just measure this relative motion, and it is more convenient if we can record and display
this motion on a computer screen. The vibration detector consists of a powerful magnet suspended at
the edge of a coil.
1. Connect the coil of the vibration detector to the input socket on the adapter of the extension
lead. Plug the adaptor output lead into the microphone input of a computer.
Hypotheses:
Make a hypothesis for each of the following questions and then answer them from the results of your
experiments:
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Are earthquakes periodic (in other words, all of the same slip, and all separated by the same
amount of time) or do they occur randomly in time and and have randomly varying size.
Are e arthquakes 'time-predictable' ? (this means that the larger the slip in the last earthquake,
the longer the wait until the next one.) This idea was formulated in the 1980's by Shimazaki
and Nakata in Japan, and has been widely used.
Justification/Geological Background:
Use your initial research to help explain briefly your predictions above. Read "Parkfield's unfilled
promise" to get you started.
Interpretation:
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For each experiment draw a graph and briefly annotate on it the general pattern, giving
maximum & minimum figures, and any anomalies etc.
Describe your findings in words.
Explain why these patterns and anomalies occurred.
Compare your findings with text books and results from other research investigations.
Locate a map of the Moon. Relate your data to the various craters that you see on the Moon,
and try to predict what type of meteor may have caused some of the craters
Sum up your findings with a conclusion, referring back to your original hypotheses.
Evaluation:
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How reliable was the experiment/procedure/equipment?
What problems or limitations were there with the experiment?
Where did it not fit in with real life situations?
How does using a brick and sandpaper experiment helps us understand real earthquakes?
What improvements could be made?
What problems did you encounter as you tried to measure the force on the force meters? How
did you deal with those problems?
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How reliable are the results and your recording of the results?
What improvements could be made to improve the recording reliability?
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How could the investigation be extended?
What new problems/questions/hypotheses could be put forward?
What other variables could be tested?