Why did we go down the Richter scale?

How do you measure the strength of earthquakes?

Measuring the intensity of an earthquake seems so obvious to us today that it is hard to imagine a news report on an earthquake without mentioning the intensity of the noise. Most of us are awestruck by the power of nature when we hear a magnitude 8 or 9 earthquake, and the destruction caused by such an earthquake, and move to the agenda with a shrug at a magnitude 3 or 4 earthquake, but we do not give our opinion on the meaning of these numbers. That's exactly what we're here for.

on bumpy ground

The Earth was formed about 4.6 billion years ago as a fairly hot body. Since then it has gradually cooled and solidified, but its core is still liquid and hot. More precisely, the inner core consists of solid metals, mainly iron and nickel, and a liquid outer core environment, at a temperature that may reach up to 10,000 degrees. The core is packed in a shell of hot and molten rocks, which is about 3,000 km thick, and its temperature is also several thousand degrees. This whole bubbling, hot and bubbling business is wrapped in a thin layer - only a few tens of kilometers - of solid rocks. More than two-thirds of this rocky surface is covered by water, and on the remaining third about eight billion people are huddled, trying to lead a normal life, without paying attention to the bomb buzzing under their feet.

The earth's crust is not uniform. Its outer part consists of huge blocks of rock, which geologists call "slabs". How huge? According to the accepted theory there are nine main plates that make up the upper part of the crust. They are in constant motion due to the currents of the liquid rocks below them, as well as due to gravity, which pulls them in the opposite direction - to the center of the earth. Sometimes, the movement causes the boards to rub against each other, or even slightly overlap each other. In the long run, it is these forces combined with pressure and temperature that cause mountains to form and create the Earth's surface as we know it. However, in the short term, these collisions and frictions are what cause earthquakes. Most of the areas prone to such tremors lie in the boundaries between the plates, such as the area of ​​Japan and the Philippines, the San Andreas rift in California and also the Syrian-African rift, of which the Arabah and the Jordan Valley are a part.

subjective measurement
Earthquakes have caused a lot of damage since time immemorial, but the idea of ​​classifying their intensity in an orderly manner is a relatively new idea. In 1902, the Italian geologist (and priest) Giuseppe Mercalli developed a scale for rating the intensity of earthquakes. His scale included 12 degrees of intensity, and the classification was made according to the effect of the noise and according to the feeling of people who experienced the tremor. For example, an earthquake that only caused the chandeliers to shake received a rating of 1 or 2, while an earthquake that destroyed many buildings and caused great public panic could have received a rating of 10. The great disadvantage of the method was its subjectivity - it was based mainly on human feelings, and it was Depends on factors that are not directly related to the natural phenomenon itself, such as the quality of the construction (in a neighborhood whose dilapidated houses are made of clay, more damage will surely be caused than in a neighborhood of solid stone houses, with the same noise intensity). Also, the Markali method did not allow to rate earthquakes that occurred in uninhabited areas, or that are only sparsely populated. In the first decades of the 20th century, scientists around the world tried to perfect the ranking method and make it more scientific. In the end, the method chosen was that of a young American researcher, Charles Richter.

global method
Richter was born in 1900 in Ohio, and after his parents' divorce, he moved with his grandfather's family to Los Angeles, where he successfully completed physics studies at Stanford University. At the age of 28, he received a doctorate in theoretical physics from the California Institute of Technology (CalTech), and the president of the university offered him a position in the new seismological laboratory at the university, where he combined his knowledge of physics with the study of the Earth. The director of the laboratory was a scientist who had just arrived from Germany, Professor Beno Gutenberg, after his promotion there was blocked due to his Jewish origin. The two new colleagues got along great, and were engaged in the task of developing a rating system for earthquakes. The original idea was to publish an orderly record of the earthquakes in California, and therefore the two researchers sought to develop a method to measure their intensity, so that it would be possible to compare them. The method developed by Richter is based on a seismograph - a device consisting of a needle sensitive to vibrations, which plots the vibrations on a roll of paper.

Richter built the scale based on the vibrations of a certain type of seismograph, a hundred kilometers away from the epicenter. Since there were very large differences in the intensities of the earthquakes in Southern California, Gutenberg suggested making the scale logarithmic. This means that a level 7 noise is ten times louder than a level 6 noise and a hundred times louder than a level 5 noise. Richter and Gutenberg published their scale in 1935. The formula they developed for earthquakes in California was soon adapted to other places in the world. However, Gutenberg refused, and she became associated mainly with Richter's name. The Richter scale outperformed many other scales developed at that time, which measured certain types of waves, or the duration of noise. The main disadvantage of the Richter scale is that it is not suitable for measuring particularly strong earthquakes, nor is it suitable for calculating the intensity of particularly strong earthquakes. After several decades in which the Richter scale would be used as the main measuring tool, it gave way to a new and more sophisticated scale.

Seismograph in the living room
The new scale - like the Richter scale - was also developed in the seismological laboratory at Cal-Tech. Professors Thomas Hanks (Hanks) and Hiro Kanamori (Kanamori) proposed a new index, which does not consider only the seismic wave, but the energy released in the earthquake. The energy is expressed in the calculation of the seismic moment, which takes into account the ground vibrations, the size of the area where they are felt and the hardness properties of the ground. However, most of these parameters are not measured in real time, but are weighted using the seismographic measurement. In terms of the measurement itself, there is no big difference between the Richter scale and the magnitude scale, however the use of a different calculation formula, which came into use in 1979, makes the magnitude scale according to moment (or in short: the magnitude scale) more accurate than the Richter scale, especially in the high intensities of the earthquakes, and in the calculation The intensity of distant earthquakes. In recent years, the magnitude scale has become the universal yardstick for measuring earthquakes. The intensities published in the media are also according to the magnitude scale, but many media outlets still report that they are according to the Richter scale, either out of habit or out of lack of awareness. It is possible that Richter's own personality also contributes to the absolute identification between him and measuring earthquakes. Until his death (in 1985), he was the light and shadow of the field, and used to respond personally to many inquiries and to every question addressed to him. Legend also has it that he kept a seismograph in the living room of his home in Los Angeles, to be informed of every earthquake.

without warning
Measuring the intensity of earthquakes is a relatively simple scientific task compared to the real challenge that geologists have been trying to deal with for decades - so far without success - to predict the strong tremors in advance. Minor earthquakes occur thousands of times a year, the vast majority of which are not felt at all. However, scientists currently have no way to estimate in advance when and where plate movements will occur that will cause considerable, even destructive, noise. Today, the researchers are trying to develop measures that will give a warning of a few minutes, such as sensitive sensors that will be buried in the ground in prone places, and will warn about relatively small movements - which are not felt on the ground - that occur a few minutes before the main noise. Such a system could allow the evacuation of people from buildings just before the noise, and save the lives of thousands, even if it does not prevent the collapse of the houses. However, so far researchers have not been able to develop such systems, and the ability to predict strong earthquakes today is not much different from the ability the prophets had thousands of years ago.

The earthquake in Nepal - as a result of the collision of the Indian plate with the Eurasian plate in the Himalayan region