A Brief History of Seismology Part 1: Earthquake Myths and Early Discoveries

It all started with a bang, movement of tectonic plates, and then the Earth as we know it today finally formed. But that's not all of course, as forming and moving of continents and tectonic plates underneath is an ongoing process. That's also one of the reasons why earthquakes have been around for quite some time now and why we’re writing a blog on seismology history.

Picture 1: Measuring and recording the seismic waves.

From Aristotle to the Invention of the First Seismograph

Although the scientific study of earthquakes – seismology – and seismology history are relatively new and seismologists didn’t provide much descriptive information on the occurrence of earthquakes until the 18th century, they recorded a few factual descriptions of earthquakes before. The earliest earthquake with descriptive information dates to 1117 B.C. in China¹ whereas earthquakes in Europe aren’t mentioned until 580 B.C. Although earthquakes have been documented, their source, effects, as well as possible precursors, were not well explained.

It wasn't until well into the 18th century that people stopped considering earthquakes as a manifestation of divine wrath and the usual response to any natural disaster at that time was. However, some of the premodern cultures, such as Greek and Chinese, developed their own naturalistic explanations for seismic shaking. In Greek culture (at around 330 B.C.), Aristotle attributed earthquakes to winds, while in Chinese (at around 200 B.C.), people were emphasizing the so-called qi: a subtle essence, which, when it got blocked, caused the Earth's shaking. These explanations have not only led to the rise of the Aristotelian view of natural disasters during the medieval times in Europe and the Middle East but also contributed to the development of studies on the origin of earthquakes as well as to some amazing inventions - amongst the most important ones is Chinese polymathic scientist and statesman Zhang Heng's (78–139) invention of the first seismoscope in 132 AD.

Nevertheless, the modern approach to seismological thinking and definition of seismology, in general, started after the destructive Lisbon earthquake in 1755 that caused seiches all over Europe. This destructive event changed the way of thinking about earthquakes: Namely, J. Michell (1724–1793) in 1761 proposed the idea of an earthquake motion caused by a wave and high-temperature steam. Although these ideas didn't lead scientists to produce any additional research, they weren't forgotten and didn't replace older theories.

Picture 2: The first seismoscope ever invented by Zhang Heng in 132 AD.

A Breakthrough in Earthquake Studies in the 19th Century

In the 18^th century, we were witness to some attempts to understand the origins of earthquakes. However, it was in the 19^th century that the public started to regard seismology and its earthquake studies as a specialization, to which the 19^th-century shift of science regarded as a profession contributed.

One of the biggest contributions of the 19th-century scientists in this field was "the accumulation of large volumes of data^1". This style of cataloging specific data was primarily influenced by German polymath, geographer, naturalist, and explorer Alexander von Humboldt (1769–1859) and was thus referred to as the »Humboldtean« style: its primary objective was to identify patterns underlying devastating events such as earthquakes. Speaking in terms of Earth science and earthquake studies he tried to discover earthquake origin as well as the possible correlation between earthquakes, meteorological events, and astronomical cycles, which led to the first systematic catalogs of "shocks".

The beginning of the 19^th century gave rise to some general studies of natural disasters and provided us with some studies of individual earthquakes. The reason behind this shift was some strong earthquakes at the end of the 18^th and at the beginning of the 19^th century, which were followed by special studies, e.g., "commissions set up by governments or local scientific societies^1". Such studies contributed to the development of seismology and its specific vocabulary and tools used to describe the (felt) effects of earthquakes, one of them being the scales of the intensity of shaking, developed by the Prussian scientist P.N.C. Egen (1793–1849) in 1828. These weren’t merely theoretical but also applied in the so-called isoseismal maps (invented by German mineralogist and geologist Johann Jakob Nöggerath (1788–1877) in 1847). The scientists of the 19^th century, among others especially German natural historian and geologist Karl Ernst Adolf Von Hoff (1771–1837) and Scottish geologist Charles Lyell (1797–1875), started to relate earthquakes to other geological processes, which resulted in some new discoveries, the most notifiable being "that earthquakes could cause vertical motions over large areas^1".

After 1830, such observations and new discoveries eventually led to a different approach in earthquake studies with an emphasis on elastic materials and their behavior. French mathematician and physicist Siméon Denis Poisson (1781–1840), among others, proposed the idea of wave motions in elastic materials that were applied to earthquakes by English mathematician and geologist William Hopkins (1793–1866) and Irish geophysicist, civil engineer, and inventor Robert Mallet (1810–1881) in 1840. This way of thinking resulted in using time observations of wave arrivals to locate earthquakes as well as in the generation of waves caused by earthquakes. Approximately during this time, (no other than) Mallet coined the term "seismology", delivered the definition for seismology, and also "constructed one of the most complete earthquake catalogs to date^1".

Picture 3: The map of tectonic plates.

First Attempts at Recording the Earthquake Motion

Mallet first defined the seismic and aseismic regions of the world in 1858; Moreover, he not only tried to provide descriptive information but also practical. That’s why he tried to apply mechanical principles to find out how and in which direction the ground moved during an earthquake as well as to determine the depth of an earthquake and to measure the velocity of its waves. Although his studies were comprehensive and helped establish seismology in the form it’s known today, they were all lacking "an adequate method of recording earthquake motion^1". Missing was a network of instruments that could record the time and other aspects of ground shaking. Such an instrument was eventually invented by the Italian physicist and meteorologist Luigi Palmieri (1807–1896) in 1856 and was recognized as the first modern seismoscope. However, its main purpose was not to record the Earth’s shaking, but rather to »measure ongoing unfelt small motions, looking for changes in the amplitude or period of these related either to weather or to earthquakes¹.«

Sources:
1) Agnew, Duncan Carr. History of Seismology. Accessed on 16-Mar-2022. Available at: https://igppweb.ucsd.edu/~agnew/Pubs/agnew.a66.pdf