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
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
Hugo Benioff developed the strain seismograph
MODERN SEISMOGRAPH TYPES
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
The second type is a sensor which measures
absolute velocity. A geophone is an example.
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
Here are some references about building
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
In addition, here are two excellent books
1. Bruce A. Bolt, Earthquakes, Freeman,
New York, 1988.
2. M. Levy and M. Salvadori, Why the Earth Quakes, Norton, London,
The following web sites offer further information:
Please send comments and questions to Tom
Irvine at: firstname.lastname@example.org