Build your own seismograph Alan Kafka, Boston College Michael Hubenthal, IRIS
Your Task design and construct a seismograph using common household and craft materials provided
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.
Seismoscopes- indicate that motion has occurred, azimuth, perhaps some simple measure of size. Seismograph– records ground motion as a continuous function of time.
First Seismoscope • AD 132, Zhang Heng of China's Han dynasty • 2 meters in diameter • Eight points around the top were dragon's heads holding bronze balls • Pendulum inside
European Seismoscopes (function) • 1703 - Proposed by J. de la Haute Feuille - bowl of mercury. • 1731 – Nicholas Cirillo - simple pendulums • 1783 - Domemico Salsano, a clock-maker and mechanic of Naples, invented a "geo-sismometro” • common pendulum, eight and a half "parisian" feet long. • equipped with a brush to record motion with slow-drying ink on an ivory slab.
Seismoscope (time) • 1784 - A. Cavalli bowl of mercury with moving pots beneath to “catch” every minute (timing never built) • 1796 - Duca della Torre • Pendulum • A record, written by a pencil attached pressed gently against paper. • Hair on the pendulum mass was a hair which would start the clock
Seismoscope (period) • 1844 – James Ford – Inverted pendulum design • Recognized value of long period instrument • common pendulum, 10-20ft = period of 4-5s
Seismograph • 1875 – Cecchi (Italy) – seismoscope • start a clock • start into motion the recording surface at the time of an earthquake.
Seismograph • 1889- von Rebeur's horizontal pendulum
To measure horizontal ground motion: A heavy mass is decoupled from the Earth by means of a pendulum.
When the ground moves, the mass tends to remain stationary because of its inertia, but the support (frame) moves with the Earth.
The movement of the Earth relative to the stationary mass is recorded on a rotating drum.
To measure vertical motion: The principle is the same, but the mass is suspended on a spring.
With a modern seismograph, the ground motion is also recorded on a computer.
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.
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)
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
The Great Sumatra Earthquake of 2004 Seismograms Recorded at Boston College Magnitude 8.7 March 28, 2005 Magnitude 9.0 December 26, 2004
Magnitude 6.7 Gulf of California January 4, 2006
Seismology = The study of seismic waves. • Seismograph = Instrument that records seismic waves as a function of time. • Seismogram = The record of ground motion that is produced by a seismograph.