Earthquake Simulation Program

Background

What is an earthquake?  The definition of an earthquake is a violent vibration of the Earth that is caused by the sudden release of energy, usually as a result of faulting, which involves the displacement of rocks along fractures.  They occur when rocks have been placed under huge amounts of pressure, for example if you take the rocks in the lithosphere, if the pressure increases very slowly, they will deform slightly.  However, the problem is that all solids have a limit and continuous pressure will result in the shattering or fracturing of them.  This is because rocks are brittle substances and will ultimately break under pressure, without warning, hence a sudden fracture, which is otherwise known as faulting.  If a rock takes a long time to deform then it will take a long time for an earthquake to occur.  After an earthquake has occurred, the fault makes adjustments, which are known as aftershocks.  These cause considerable damages to the buildings already weakened by the earthquake itself.  Aftershocks can be persistent from a few days up to a few months after the earthquake has occurred, depending on the size of the earthquake.

However, in order to understand how they occur, we need to address the plate tectonic theory.  This theory suggests that the Earth be broken up into several plates, which are thick slabs of rock.  Earthquakes only occur in the outer, brittle portions of these plates, where temperatures in the rock are relatively low.  Deep down inside the Earth, about 100-250 kilometres to be precise, in the low velocity zone (asthenosphere), convection cells induces stress that results in the movement of the overlying plates.

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-

-

Medium

(D2)

-

-

-

-

-

Far

(D3)

-

-

-

-

-

3

Close

(D1)

60

80

20

1

0.5

Medium

(D2)

128

194

66

0.5

0.5

Far

(D3)

188

284

96

1

0.5

5

Close

(D1)

50

82

32

1

1.5

Medium

(D2)

122

190

68

1

1

Far

(D3)

182

280

98

0.5

1

7

Close

(D1)

48

71

23

0.5

1

Medium

(D2)

126

186

60

1

1

Far

(D3)

183

280

97

0.5

1

9

Close

(D1)

48

70

22

1.5

3.5

Medium

(D2)

122

188

66

1.5

2.5

Far

(D3)

185

280

95

1

2

When I was calculating the amplitude, it was difficult to measures exactly from half the wave, due to the reasons just mentioned, which therefore resulted in human error.  The seismic print out was computer generated, which could have produced inaccurate lines in the seismic printouts, again result in an anomalous result.

However, despite this, this investigation was on the whole rather successful.  I was able to collate enough information that could be used to answer what I was investigating.  The method was followed exactly as it was stated; I kept the detectors and variables at a constant position, in order to ensure a fair test and consistency.  The main flaws in this investigation were down to the analysis of the results.  As the depth was constant at 30 km, for both experiments, this made the investigation a lot easier, as there were no major discontinuities.

Therefore I feel that this investigation was not entirely reliable and in order to improve this, several steps need to be undertaken.  Firstly, I could increase the scale on the seismic printout so that it is easy to decipher when waves are arriving and the amplitude because the waves will be larger.  I could use a thinner pencil or even with the aid of lasers for plotting accurate arrival times and amplitudes.  In addition to this, I would find an average of the readings at each detector so that the readings would be more accurate.  For example, instead of having 1 detector at each detector, as in this experiment, I would have several detectors at each detector so that an average reading can be worked out.

I have only investigated two factors in this investigation and to further it I could investigate how depth, incompressibility and density affect the arrival time and amplitude of p and s-waves.

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