Seismology
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 The word comes from the Greek word seismic, for
shaking.
 It is the branch of Geology which has provided the
most comprehensive interpretation of the
composition, thickness, density, structure and
physical state of each layer of the Earth’s interior.
 It originated in around 1880 with the development of
the seismograph
Seismograph
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 An instrument that can detect, record, and measure
the intensity of earthquake waves
An Earthquake
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 This is simply a movement within the Earth.
 Most earthquakes result from movements along
faults in rocks where there is a build up of pressure.
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 The shifting of rock along faults can be vertical or
horizontal.
Wave Types
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 There are two general types of seismic waves;
 Body Waves – these waves travel within the Earth
 Surface Waves – these waves travel on the surface of
the Earth
 Surface waves cause the most destruction
Body Waves
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 There are two types of body waves
 Primary waves or P-waves
 Secondary waves or S-waves
P-waves
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Are the fastest seismic waves
Travel through solids, liquids, and gases
6-7km/sec near the earth surface
These waves travel much like sound waves, know as
compression or longitudinal waves.
S-waves

 They travel slowly and are the second wave to arrive
at a seismograph station
 3.5km/s on the earth surface
 Can only travel through a solid
 These waves travel much like water waves, know as a
transverse waves.
Surface Waves

 Surface waves are the slowest of all the waves set off
by an earthquake
 The two important types are;
 Love waves
 Rayleigh waves
Love waves
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 These waves move horizontal, with no vertical
displacement.
Rayleigh waves
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 These waves move in an elliptical path
Locating and Measuring
Earthquakes
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 A seismograph can indicate the magnitude of the
earthquake.
 The types of waves can also be determined at the
station.
 The time interval between seismic waves recordings
that reach a seismic station is what is used to
determine the location of an earthquake.
 The further the waves are apart on a arrival at a
station the further one is away from the epicenter.
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Path of An Earthquake
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 Seismic body waves penetrate Earth’s interior.
 The path a wave will take within Earth’s interior
depends on the wave’s velocity
 The velocity in turn in dependent on the type of
material encountered by the wave
 Homogenous materials are straight paths
 Encountering different density will cause the wave to
either reflect or refract
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Model of the Earth’s
Interior
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 From the recording of the many and different
seismic body wave paths, along with the time
intervals between the arrival of these waves scientist
have been able to develop the model of the earth’s
interior as we know it today.
 It has taken many observations, people and years to
come up with this picture.
 It is not a perfect picture and will be improved with
time
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