(WHTM) — April 26 is the birthday of Seismologist Charles Richter, co-creator with Beno Gutenberg of the Richter Scale, which measures the intensity of earthquakes.
In the early 1930s, the field of seismology (the study of earthquakes) was really in need of a way to measure the strength and destructive power of quakes. About the only measurement system available at the time was the highly subjective Mercalli Scale, which classified earthquakes based on the effects on buildings, and how terrified people were. But in the 1920s the first seismographs appeared, which allowed seismologists to directly measure the shock waves being generated by earthquakes and plot them on sheets of paper.
But how to interpret the seismograph data? In 1928 Kiyoo Wadati of the Central Meteorological Observatory of Japan published a paper, “Shallow and Deep Earthquakes”. It compared below surface displacements of the Earth’s crust against distance from an earthquake epicenter and inspired Richter and Gutenberg to devise what became known as the Richter Scale.
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One of the problems they faced was squeezing the data down to a manageable size. If they used a linear scale-starting with one, two is twice as powerful, three is three times as powerful, and so forth they would have needed hundreds of levels, and would have had to juggle an inordinate amount of zeros. Instead, they created a logarithmic scale. Each number on the Richter Scale represents an earthquake ten times more powerful than the number preceding it. (A five is ten times more powerful than a four, a six is ten times more powerful than a five, and so on.) Richter described it as a “magnitude” scale, borrowing a term from an early interest in astronomy.
The Richter scale caught on, both with scientists and the general public. Every time there’s an earthquake, news media will announce its intensity as “so and so on the Richter Scale.” It’s one of those pieces of scientific terminology almost everybody’s heard.
The odd thing is, seismologists aren’t really using the Richter scale anymore. The original Richter Scale parameters worked best in Southern California, where both Richter and Gutenberg lived and were less accurate elsewhere. In the 1970s it was replaced by other magnitude scales which give more accurate readings, especially with newer, more sensitive seismographs. But they all keep Richter and Gutenberg’s idea of measuring earthquakes using a logarithmic scale, and the various scales sync up to a certain extent, so we can expect “Richter Scale” to be part of the vocabulary for a long time to come.
(This area has had its share of minor earthquakes over the years; in 2020 Dover had two earthquakes in 24 hours, magnitudes 1.6 and 1.8. In 2019 2.8 East Berlin had an M 2.8, and Honey Grove, about 11 miles southwest of Mifflintown, had an M 3.4. In 2017 Conestoga had an M 2.3. In 2010 a magnitude 2.9 quake was felt on both the West and East Shores. And in 2008 from October through December the Dillsburg area had a cluster, or swarm, of 49 Earthquakes, all less than magnitude 3.0. )