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Seismology = The study of seismic waves. Seismograph = Instrument that records seismic waves.

Seismology = The study of seismic waves. Seismograph = Instrument that records seismic waves. Seismogram = The record of ground motion that is produced by a seismograph . How does a seismograph work?. To measure horizontal ground motion:.

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Seismology = The study of seismic waves. Seismograph = Instrument that records seismic waves.

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  1. Seismology = The study of seismic waves. • Seismograph = Instrument that records seismic waves. • Seismogram = The record of ground motion that is produced by a seismograph.

  2. How does a seismograph work?

  3. To measure horizontal ground motion: A heavy mass is decoupled from the Earth by means of a pendulum.

  4. When the ground moves, the mass tends to remain stationary because of its inertia, but the support (frame) moves with the Earth.

  5. The movement of the Earth relative to the stationary mass is recorded on a rotating drum.

  6. To measure vertical motion: The principle is the same, but the mass is suspended on a spring.

  7. With a modern seismograph, the ground motion is also recorded on a computer.

  8. AS1 Seismograph

  9. The Great Sumatra Earthquake of 2004 Seismograms Recorded at Boston College Magnitude 8.7 March 28, 2005 Magnitude 9.0 December 26, 2004

  10. Magnitude 6.8 April 10, 2005 Magnitude 8.7 March 28, 2005 Magnitude 9.0 December 26, 2004 Seismograms are shown on the same scale. AS1 Seismograms Same Distance, Different Magnitudes Three Sumatra Earthquakes Recorded at Weston Observatory Boston College ∆=133° Seismograms are shown on the same scale.

  11. Magnitude 6.7 Gulf of California January 4, 2006

  12. Same Magnitude, Different Distances Seismograms are shown on the same scale. El Salvador Magnitude 7.7, January 13, 2001 ∆=33° India Magnitude 7.7, January 26, 2001 ∆=106° AS1 Seismograms El Salvador and India Earthquakes Recorded at Devlin Hall Boston College

  13. Same Earthquake, Different Distances Seismograms are shown on the same scale. Phoenix Country Day School, Paradise Valley, AZ ∆=7° AS1 Seismograms Weston High School,Weston, MA ∆=38° Parkfield, CA Earthquake Magnitude 6.0, 09/28/04 Time (sec/102)

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