The birth of Richter Scale, the device that measures earthquake magnitudes
Recently, the south-eastern part of Turkey and almost the whole of Syria have been hit with an earthquake of 7.8 magnitude. So far, the death toll stands at 4300, while the loss of infrastructure and property seems to be abysmal. Talking about earthquakes and their magnitudes makes us curious about the backstory of Richter Scale. It is a logarithmic scale used in the field of seismology to quantitatively determine the energy or size released by an earthquake. Today, let us trace the origin of Richter Scale.
The pre-Richter Scale era
Until the first half of the 20th century, before the Richter Scale was developed, the magnitude of an earthquake was calculated using various seismic intensity scales such as the Rossi-Forel Scale and Mercalli Scale. Both of these scales subjectively measured the intensity (quantity of energy released) of the earth’s shaking as observed near the epicentre of an earthquake. However, in 1883, a British seismologist named John Milne realised that these measurements were often inaccurate and that the seismic shock waves were often far-reaching. His hypothesis was further confirmed in 1899 by German seismologist E.Von Rehbur Paschvitz who observed shock waves of a Tokyo earthquake in Berlin. This discovery made the entire seismic community figure out that the magnitude of a single earthquake may vary from place to place and the extent of impact.
Fast forward to 1920, an American seismologist named Harry O. Wood and an American astronomer named John A. Anderson developed the Wood-Anderson Seismograph, one of the first practical instruments to measure seismic waves. But guess what? They had no effective scale available to install into their newly invented device.
Charles F. Richter saves the day!
Wood and Anderson set up a network of their seismographs across Southern California while still looking for a suitable scale for their instrument. This is when Wood accidentally came across a young intern named Charles F. Richter who was working at the California Institute of Technology and was greatly interested in the brand-new field of seismology. Wood was impressed with his passion and gave him the job of managing the seismographs and locating the earthquakes generating seismic waves.
Meanwhile, in 1931, a Japanese scientist named Kiyoo Wadati revealed to the world how he measured many strong earthquakes in Japan taking into consideration the amplitude of the shaking observed at various distances from the epicentre. But there were some problems with his method. In absence of a proper scale, all his measurements were mere estimates, which meant that all the correlation between the amplitude and the distances were rough figures. Hearing this, Richter along with his colleague Beno Gutenberg devised a scale that took both the distances and the amplitude into consideration. Their goal was simple: To precisely express the distinct magnitudes of earthquakes and determine why some earthquakes are strong and the others are weak, why some destroy civilisations while others are not even felt.
Here's what Richter planned differently. Firstly, he made his scale logarithmic meaning that each scale represented a tenfold (now 32-fold) increase in magnitude. He also set his scale’s neutral point at zero which would determine the epicentre. Finally, he tried his scale in Wood and Anderson’s device and it fit and worked perfectly. Thus, in 1935, the magnitude scale was born that later came to be known as Richter Scale on Wood’s suggestion.
For the first time ever, it was Richter who showed the world that to properly measure the magnitude of an earthquake, it is the amount of ground vibration that needs to be considered rather than the physical size of the earthquake fault. This was exactly how astronomers measured the luminosity of stars.
Originally the Richter Scale was invented to measure an earthquake of moderate magnitude (≥3 to ≤7). However, with modern technological advancements, Richter scale can measure earthquake magnitudes ranging below zero (negative magnitudes) to as high as 10. However, till date, no earthquake of more than 8.6 Richter (1960 Chile earthquake) has been measured.