A Chinese scientist named Chang Heng invented a seismoscope about 132 A.D. This instrument did not make a time recording of the earthquake oscillation. Rather it indicated the direction of the principal impulse of the earthquake.
The modern seismograph was invented in the late 1800s. There are two basic types. One type uses a mass suspended by a pendulum. The other is based on a device which responds to strain.
J.A. Ewing invented a pendulum seismograph in 1880. Lucien LaCoste improved this design.
A Ewing three-component seismograph at Mt. Hamilton made a partial recording of the 1906 San Francisco earthquake.
Many other scientists added further improvements.
H.O. Wood and J. Anderson developed a seismograph with a mass suspended by torsion. This seismograph became the standard for magnitude determination of local shocks. This magnitude is the Richter scale. Charles Richter developed this scale in 1935.
Hugo Benioff developed the strain seismograph in 1935.
Relative Displacement
The first type is a device which relies on the measurement of relative displacement. The ground moves underneath some pendulum-type device. The pendulum itself remains unmoved due to its own inertia. Note that inertia is resistance to acceleration. The pendulum thus serves as a reference point. The relative displacement is measured between the ground and this reference point.
Absolute Velocity
The second type is a sensor which measures absolute velocity. A geophone is an example.
Absolute Acceleration
The third type is an accelerometer, which measures absolute acceleration. The accelerometer is easier to use, but it is only useful for measuring "strong motions" nearby the earthquake epicenter. Note that displacement can be calculated from acceleration.
The following comments apply to all types:
1. The output signal of the measuring device may require some form of mechanical or electrical amplification.
2. Some type of recording method is required, such as a strip chart recorder or a computer. The computer is called a "data acquisition system."
Here is a link to a page describing my Lehman Seismometer.
Here are some references about building seismographs:
1. "The Amateur Scientist," Scientific American, pp 152-162, January, 1963.

2. Walker, J., "How to build a simple seismograph to record earthquake waves at
home," Scientific American, vol 241, #1, pp. 152-161, 1979.
3. Averill, G.E., "Build your own seismograph: An earth-shaking, in-class
project," The Science Teacher, vol 62, #3, pp. 48-52, March 1995.
In addition, here are two excellent books about earthquakes:
1. Bruce A. Bolt, Earthquakes, Freeman, New York, 1988.
2. M. Levy and M. Salvadori, Why the Earth Quakes, Norton, London, 1995.
The following web sites offer further information:
Seismometer Designs
Seismograph Visual
Please send comments and questions to Tom Irvine at:
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