Who Invented the Seismograph?

And Other Innovations Surrounding Earthquake Study

Milne's seismoscope (1890) replica - National Museum of Nature and Science, Tokyo

Daderot / Wikimedia Commons

When discussing earthquake study and the innovations built around it, there are multiple ways to look at it. There is the seismograph, used to detect earthquakes and record information about them, such as force and duration. There is also a number of instruments created to analyze and record other earthquake details like intensity and magnitude. These are some of the tools that shape the way we study earthquakes.

Definition of a Seismograph

Seismic waves are the vibrations from earthquakes that travel through the earth. They are recorded on instruments called seismographs, which follow a zigzag trace that shows the varying amplitude of ground oscillations beneath the instrument. The sensor part of a seismograph is referred to as the seismometer, while the graphing capability was added as a later invention.

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 seismograph stations.

Chang Heng's Dragon Jar

Around 132 CE, Chinese scientist Chang Heng invented the first seismoscope, an instrument that could register the occurrence of an earthquake called a dragon jar. The dragon jar was a cylindrical jar with eight dragon heads arranged around its brim, each holding a ball in its mouth. Around the foot of the jar were eight frogs, each directly under a dragonhead. When an earthquake occurred, a ball dropped from a dragon's mouth and was caught by the frog's mouth.

Water and Mercury Seismometers

A few centuries later, devices using water movement and later, mercury were developed in Italy. More specifically, Luigi Palmieri designed a mercury seismometer in 1855. Palmieri's seismometer had U-shaped tubes arranged along compass points and filled with mercury. When an earthquake hit, 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 movements.

Modern Seismographs

John Milne was the English seismologist and geologist who invented the first modern seismograph and promoted the building of seismological stations. In 1880, 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, which funded the invention of seismographs. Milne invented the horizontal pendulum seismograph in the same year.

After World War II, the horizontal pendulum seismograph was improved with the Press-Ewing seismograph, developed in the United States for recording long-period waves. This seismograph uses a Milne pendulum, but the pivot supporting the pendulum is replaced by an elastic wire to avoid friction.

Other Innovations in Earthquake Study

Understanding Intensity and Magnitude Scales

Intensity and magnitude are other important areas in the study of earthquakes. Magnitude measures the energy released at the source of the earthquake. It is determined from the logarithm of the amplitude of waves recorded on a seismogram at a certain period. Meanwhile, intensity measures the strength of shaking produced by the earthquake at a certain location. This is determined by effects on people, human structures, and the natural environment. Intensity does not have a mathematical basis—determining intensity is based on observed effects.

Rossi-Forel Scale

Credit for the first modern intensity scales goes jointly to Michele de Rossi of Italy and Francois Forel of Switzerland, who both independently published similar intensity scales in 1874 and 1881, respectively. Rossi and Forel later collaborated and produced the Rossi-Forel Scale in 1883, which became the first scale to be widely used internationally.

The Rossi-Forel Scale used 10 degrees of intensity. In 1902, Italian volcanologist Giuseppe Mercalli created a 12-degree scale.

Modified Mercalli Intensity Scale

Though there have been numerous intensity scales created to measure the effects of earthquakes, the one currently employed by the United States is the Modified Mercalli (MM) Intensity Scale. It was developed in 1931 by American seismologists Harry Wood and Frank Neumann. This scale is composed of 12 increasing levels of intensity that range from imperceptible shaking to catastrophic destruction. It does not have a mathematical basis; instead, it is an arbitrary ranking based on observed effects.

Richter Magnitude Scale

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 earthquake might be computed as moderate, 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.

When it was first created, the Richter Scale could only be applied to the records from instruments of identical manufacture. Now, instruments are carefully calibrated with respect to each other. Thus, magnitude can be computed using the Richter Scale from the record of any calibrated seismograph.