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

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

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

4. 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.

5. Seismograph – records ground motion as a continuous function of time.
Seismoscopes - indicate that motion has occurred, azimuth, perhaps some simple measure of size.
Seismograph – records ground motion as a continuous function of time.

6. 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
On at least one occasion, probably at the time of a large earthquake in Gansu in AD 143, the seismoscope indicated an earthquake even though one was not felt. The available text says that inside the vessel was a central column that could move along eight tracks; this is thought to refer to a pendulum, though it is not known exactly how this was linked to a mechanism that would open only one dragon's mouth. The first ever earthquake recorded by this seismograph was supposedly somewhere in the east. Days later, a rider from the east reported this earthquake.[3][4]

7. European Seismoscopes (function)
Proposed by J. de la Haute Feuille - bowl of mercury.
1731 – Nicholas Cirillo - simple pendulums
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.
In 1703, J. de la Haute Feuille proposed filling a bowl to the brim with mercury, so that an earthquake would cause some of the mercury to spill out (de la Haute Feuille, 1703; Favaro, 1884). In order to determine the direction of the shock, the mercury spilling out in each of the eight principal directions of the compass was to be collected in cavities or other containers.
The honor of being the first European to record the use of a mechanical device as an aid to the study of earthquakes goes to Nicholas Cirillo (1747). Cirillo employed simple pendulums in an investigation of a series of earthquakes in Naples in He observed the amplitude of pendulum oscillations at the locations where the shaking was most severe, and also at locations somewhat removed from the zone of severest shaking. He found the amplitude to decrease with the inverse square of the distance, a result he anticipated from "the common laws in other sorts of motions" (Cirillo, 1747, p. 682).

8. Seismoscope (time)
A. Cavalli bowl of mercury with moving pots beneath to “catch” every minute (timing never built)
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

9. Seismoscope (period) 1844 – James Ford – Inverted pendulum design
Recognized value of long period instrument
common pendulum, 10-20ft = period of 4-5s

10. Seismograph 1875 – Cecchi (Italy) – seismoscope start a clock
start into motion the recording surface at the time of an earthquake.

11. Seismograph 1889- von Rebeur's horizontal pendulum
Much of the next phase of the development (to the present) was focused on using electronics to both extend the dynamic range of the instrument while also minaturizing them.

13. How does a seismograph work?

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

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

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

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

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

19. AS1 Seismograph

21. Three Sumatra Earthquakes
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.
AS1 Seismograms
Same Distance,
Different Magnitudes
Three Sumatra Earthquakes
Recorded at
Weston Observatory
Boston College
∆=133°
Seismograms are shown on the same scale.

22. Parkfield, CA Earthquake
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)

23. 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

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

27. Magnitude 6.7
Gulf of California
January 4, 2006

28. 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.