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Seismology

Seismology. Seismology. 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.

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Seismology

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  1. Seismology

  2. Seismology • 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

  3. Seismograph • An instrument that can detect, record, and measure the intensity of earthquake waves

  4. An Earthquake • 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.

  5. The shifting of rock along faults can be vertical or horizontal.

  6. Wave Types • 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

  7. Body Waves • There are two types of body waves • Primary waves or P-waves • Secondary waves or S-waves

  8. P-waves • 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.

  9. 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.

  10. 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

  11. Love waves • These waves move horizontal, with no vertical displacement.

  12. Rayleigh waves • These waves move in an elliptical path

  13. Locating and Measuring Earthquakes • 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.

  14. The further the waves are apart on a arrival at a station the further one is away from the epicenter.

  15. Path of An Earthquake • 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

  16. Model of the Earth’s Interior • 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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