1. Build your own seismograph Alan Kafka, Boston College Michael Hubenthal, IRIS

2. We didn’t feel it so how do we know?

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

4. Your Task design and construct a seismograph using common household and craft materials provided

5. An excellent design will be… made of the common inexpensive materials provided for this exercise; capable of determining the relative size of each disturbance it measures; capable of measuring vibrations continuously for at least one minute; capable of capturing the time when these disturbances occurred; capable of measuring vibrations from three different sources: a bang on or shaking of the table holding the seismograph; a person jumping up and down on the floor next to the table on which your seismograph is located; and a ball bounced off of a wall or floor nearby.

7. How does a seismograph work?

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

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

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

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

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

13. AS1 Seismograph

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

16. Phoenix Country Day School, Paradise Valley, AZ ∆=7° Weston High School,Weston, MA ∆=38° Parkfield, CA Earthquake Magnitude 6.0, 09/28/04 Same Earthquake, Different Distances Seismograms are shown on the same scale. Time (sec/10 2 ) AS1 Seismograms

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

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

21. Magnitude 6.7 Gulf of California January 4, 2006