[Physics Class Notes] on Richter Scale Pdf for Exam

This scale was devised in 1935 by the seismologist of America, Charles F. Richter and Beno Gutenberg. Here, we are going to discover a few more details about the topic Richter scale. Although the science which is the modern scientific practice has replaced the original Richter scale with other scales which are more-accurate, the Richter scale is still often mentioned erroneously in news reports of earthquake severity as the catch-all name for the logarithmic scale upon which earthquakes are measured.

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Seismograph and Richter Scale

The term seismometer is the internal part of the seismograph which may be a pendulum or we can say that a mass which is mounted on a spring. However, it is often used synonymously with the term  “seismograph”.

The term seismographs are said to be the instruments which are used to record the motion of the ground during an earthquake. They are installed in the ground throughout the world and then they are operated as part of a network of seismographs. The earliest “seismoscope” was said to be invented by the Chinese philosopher Chang Heng in A.D. 132. However, this did not record the earthquakes instead it only indicated that an earthquake was occurring. The first seismograph was developed in 1890.

A seismograph is mounted securely onto the surface of the earth so that when the earth shakes the entire unit shakes with it except for the mass on the spring, it is so because of the inertia that remains in the same place. As the seismograph is said to shake under the mass we can say that the recording device on the mass records the relative motion which is between itself and the rest of the instrument. Thus we need to notice here that this is the recording of the ground motion. In reality, these mechanisms which we have discussed are no longer manual but instead work by measuring electronic production of changes that too by the motion of the ground with respect to the mass.

A seismogram is said to be the recording of the shaking of the ground at the specific location of the instrument. On a seismogram, we can say that the horizontal axis = time which is measured in seconds and the Vertical axis= ground displacement usually measured in millimetres. When there is No Earthquake reading there is just a straight line except for small wiggles caused by local disturbance or we can term it as “noise” and the time markers. The seismograms are now digital so there are no more paper recordings.

Limitations of Richter Scale Measures

The Richter scale was originally devised to measure the magnitude of earthquakes of moderate size that is for magnitude 3 to magnitude 7 by assigning a number that would allow comparing the size of one earthquake with another. The scale was said to be developed for tremors occurring in southern California that were recorded using the Wood-Anderson seismograph and whose epicentres were less than 600 km or 373 miles from the location of the seismograph. However, the present-day seismographs may be calibrated to compute Richter magnitudes, as well as the modern methods for measuring earthquake magnitude, have been developed to produce results that remain consistent with those measured using the Richter scale.

The scale of Richter is also known as the Richter Magnitude Scale. It is said to be a measure of the strength of earthquakes which was developed by Charles F. Richter and presented in his landmark 1935 paper. where he named it the “magnitude scale”. Later this was revised and renamed the local magnitude scale that was denoted as ML or ML .

Because of various shortcomings of the ML  scale, most seismological authorities now use other scales such as the moment magnitude scale that is Mw  to report the magnitude of the earthquake but much of the news media still refers to these as “Richter” magnitudes. All the scales of the magnitude retain the logarithmic character of the original and are scaled to have roughly comparable numeric values that are said to be typically in the middle of the scale.

Other Scales to Measure Earthquake 

There are a number of ways in which we can measure the magnitude of an earthquake. Other scales which are based on wave amplitudes and total earthquake duration which were developed for use in other situations and they were designed to be consistent with the scale of Richter’s.

Unfortunately, we here say that many scales such as the Richter scale do not provide accurate estimates for large earthquake magnitude. Today the moment magnitude scale which is abbreviated MW is preferred because it works over a wider range of earthquakes and is applicable globally. The magnitude moment scale is based on the total moment release of the earthquake. The moment is said to be a product of the distance and a fault which is moved and the force required to move it. It is derived from modelling recordings of the earthquake at multiple stations. The magnetic moment generally estimates about the same as Richter magnitudes for small to large earthquakes. But only the moment magnitude scale is said to be capable of measuring M8 and greater events accurately.