The history, functionality, use and advantages of the Richter Scale

Abstract

The Richter Scale is a quantitative measure of the magnitude of an earthquake. It has been invented in 1935 by Charles F. Richter and is based the amplitude measured by a seismograph with a correction factor for the distance from the centre ofthe earthquake from which the measurement is taken. This measurement is totally independent from the damage that it might cause. Although invented in 74 years ago, it is still in use and has many advantages compared to the other scales used for earthquakes.

The Richter Scale

The following paper is about the Richter Scale, a measure used to compare earthquakes to each other. Everybody should have heard about this scale, since it is mentioned in every respectable newspaper. The principle ofthis scale was invented in 1935 and has not been changed since then. Even though it is a scale for ground motion on the earth, it has been used for measuring thousands of Moon-quakes and two quakes on the planet Mars.

The magnitude of an earthquake on the Richter Scale is calculated from the measured peak amplitude. A peak amplitude is the hight with which the earth goes up. It is measured by several seismographs, spread in the area in which the earthquake occurs.

Avery simple example of a seismograph can be found on HowStuffWorks.com and it is simply a large mass hung from the ceiling with a pen, which can just reach a piece of paper on a table under it. If an sufficient strong earthquake occurs, the pen would draw a line on the paper. This may work for one quake, but ifthere are aftershocks, a measurement overtime is needed. This can easily be built in attaching a roll of paper to a motor which slowly pulls the paper over the table.

This simple type of sensor might have been used 100 years ago, but today the sensors are made more sensitive by using levers or electronics and the mass that the seismograph is attached to has a weight of 1,000 pounds or more. The combination of both, levers and heavy weight gives an accuracy, that even gives negative results, which have not been thought of as the Richter Scale was first invented. Nevertheless, these measurements are accepted in the scientificworld. To get an idea, which values on the Richter Scale can be cause by which events, a table with various Richter Scale magnitudes and their cause can be found in the table section in the end ofthis paper.

The further procedure, after the data is collected from one seismograph, is to take the mean value of all the sensors, which took data related to this quake. This is necessary, since the data is often different depending on the underground on which the seismograph is placed and the distance to the centre ofthe earthquake. The earthquake can be felt differently by the sensor as well, what depends on the nature, the location and the size ofthe ground motion. Therefore a mean value is evaluated which is plugged in this formula as the hight in mm:

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The part ofthe formula “ [illustration not visible in this excerpt] “ is the distance correction factor. It includes the distance between the seismograph and the centre ofthe earthquake in the calculations. Its functionality is easy, since it works with the difference between the time as the earthquake was created and the time when ground motion reaches the seismograph, which then notices the ground motion. This time is called the S-P time. As an example, if an earthquake occurs at 4.00.00 am and the sensor records the earthquake at 4.00.10 am, the S-P time, [illustration not visible in this excerpt], is:

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Richter wrote this system, which includes the distance in the calculations, down in 1958 in his book Elementary Seismology. To estimate an earthquake's magnitude a nomogram has been developed. It solves the mathematical equation quickly and gives a rough estimation ofthe magnitude.

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