Heng invented the first seismoscope called the dragon jar
In the history of the innovations
surrounding earthquake study, we have to look at two things: the devices
that recorded earthquake activity and the measurement systems written to
help interpret that data. Remember that the Richter scale is not a physical
device, but a mathematical formula.
Intensity and Magnitude Scales
Magnitude measures the energy released
at the source of the earthquake. The magnitude of an earthquake is determined
from the logarithm of the amplitude of waves recorded on a seismogram at
a certain period. Intensity measures the strength of shaking produced by
the earthquake at a certain location. Intensity is determined from effects
on people, human structures, and the natural environment. Intensity does
not have a mathematical basis; determining intensity is based on observed
The first reported use of any measurement
of earthquake intensity has been attributed to the Italian Schiantarelli,
who recorded the intensity of the 1783 earthquake that occurred in Calabrian,
The credit for the first modern intensity
scales goes jointly to Michele de Rossi of Italy (1874) and Francois Forel
of Switzerland (1881), who both independently published similar intensity
scales. Rossi and Forel later collaborated and produced the Rossi-Forel
Scale in 1883. The Rossi-Forel Scale used ten degrees of intensity and
became the first scale to be widely used internationally. In 1902, Italian
volcanologist Giuseppe Mercalli created a twelve-degree scale of intensity.
Although numerous intensity scales
have been developed over the last several hundred years to evaluate the
effects of earthquakes, the one currently used in the United States is
the Modified Mercalli (MM) Intensity Scale. It was developed in 1931 by
the American seismologists Harry Wood and Frank Neumann. This scale, composed
of 12 increasing levels of intensity that range from imperceptible shaking
to catastrophic destruction, is designated by Roman numerals. It does not
have a mathematical basis; instead, it is an arbitrary ranking based on
The Richter Magnitude Scale was developed
in 1935 by Charles F. Richter of
the California Institute of Technology. On the Richter Scale, magnitude
is expressed in whole numbers and decimal fractions. For example, a magnitude
5.3 might be computed for a moderate earthquake, and a strong earthquake
might be rated as magnitude 6.3. Because of the logarithmic basis of the
scale, each whole number increase in magnitude represents a tenfold increase
in measured amplitude; as an estimate of energy, each whole number step
in the magnitude scale corresponds to the release of about 31 times more
energy than the amount associated with the preceding whole number value.
At first, the Richter Scale could
be applied only to the records from instruments of identical manufacture.
Now, instruments are carefully calibrated with respect to each other. Thus,
magnitude can be computed from the record of any calibrated seismograph.
Seismic waves are the vibrations
from earthquakes that travel through the Earth; they are recorded on instruments
called seismographs. Seismographs record a zigzag trace that shows the
varying amplitude of ground oscillations beneath the instrument. Sensitive
seismographs, which greatly magnify these ground motions, can detect strong
earthquakes from sources anywhere in the world. The time, location and
magnitude of an earthquake can be determined from the data recorded by
Around 132 AD, Chinese scientist
Chang Heng invented the first seismoscope, an instrument that could register
the occurrence of an earthquake. Heng's invention was called the dragon
jar (see picture above). The dragon jar was a cylindrical jar with eight
dragonheads arranged around its brim; each dragon had a ball in its mouth.
Around the foot of the jar were eight frogs, each directly under a dragonhead.
When an earthquake happened a ball dropped from a dragon's mouth and was
caught by the frog's mouth.
A few centuries
later, devices using water movement and later mercury were developed in
Italy. In 1855, Luigi Palmieri of Italy
designed a mercury seismometer. Palmieri's seismometer had U-shaped tubes
filled with mercury and arranged along the compass points. When an earthquake
happened, the mercury would move and make electrical contact that stopped
a clock and started a recording drum on which the motion of a float on
the surface of mercury was recorded. This was the first device that recorded
the time of the earthquake and the intensity and duration of any movement.
Milne was the English seismologist and geologist who invented the first
modern seismograph and promoted the building of seismological stations.
Sir James Alfred Ewing, Thomas
Gray and John Milne, all British scientists working in Japan, began to
study earthquakes. They founded the Seismological Society of Japan and
the society funded the invention of seismographs. Milne invented the horizontal
pendulum seismograph in 1880.
The horizontal pendulum seismograph
was improved after World War II with the Press-Ewing seismograph, developed
in the United States for recording long-period waves. It is widely used
throughout the world today. The Press-Ewing seismograph uses a Milne pendulum,
but the pivot supporting the pendulum is replaced by an elastic wire to
Early History of Seismometry
This is an excellent full history of the seismograph.
on Seismographs, Seismometry, Earthquakes, and More
photo provided by LOC
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