How Earthquakes Are Measured? : Its Not Richter Scale

Posted on Posted in science, technology

How Richter Scale measures Earthquake?

Sesimic waves are vibrations generated from the earthquake that travel through the earth,are measured by some instruements through seismographs.

Seismographs record a zig-zag form of earthquake vibrations, that shows the changing amplitude of ground vibrations beneath the instrument.

Image result for moment magnitude scale of earthquake measuring

 Seismographs are which are very sensitive, which greatly magnify these ground vibrations, can detect strong earthquakes from sources anywhere in the world.

The time, locations, and magnitude of an earthquake can be determined from the data recorded by seismograph stations.

Richter Scale

Image result for moment magnitude scale of earthquake measuring

Richter Scale was developed by Charles F Richter as a mathematical device to compare the size of earthquakes.

The magnitude of an earthquake is determined from the logarithm of the amplitude of waves recorded by seismographs.

Adjustments are included for the variation in the distance between the various seismographs and the epicenter of the earthquakes. On the Richter Scale, magnitude is expressed in whole numbers and decimal fractions.

For example, a magnitude 5.3 might be computed for a moderate earthquake, and a strong earthquake might be rated as magnitude 6.3.

Because of the logarithmic basis of the scale, each whole number increase in magnitude represents a tenfold increase in measured amplitude.

Image result for moment magnitude scale of earthquake measuring

Each whole number step in the magnitude scale corresponds to the release of about 31 times more energy than the amount associated with the preceding whole number value.

Earthquakes having magnitude of approx 2.0 or less are usually called micro earthquakes are generally recorded only on local seismographs.

The Richter Scale is not commonly used anymore, as it has been replaced by another scale called the moment magnitude scale which is a more accurate measure of the earthquake size.

Drawbacks of Richter Scale

Unfortunately, the Richter scale and many other magnitude scales which have been proposed have some drawbacks.  For one, the Richter scale is capped at a magnitude of 7.0, meaning that all larger earthquakes would always have a magnitude of 7.0 or less.

 Also, the Richter scale only describes the maximum wave amplitude, and does not give any indication of the total energy that is released by the event.

Image result for moment magnitude scale of earthquake

The concept of seismic moment was introduced in 1966, but it took 13 years before the Moment scale was designed.

The reason for the delay was that the necessary spectra of seismic signals had to be derived by hand at first, which required personal attention to every event.

Faster computers than those available in the 1960s were necessary and seismologists had to develop methods to process earthquake signals automatically.

How it Works?

The moment magnitude  scale was introduced in 1979 by Caltech seismologists Thomas C. Hanks and Hiroo Kanamori to address the shortcomings of the Richter scale (detailed above) while maintaining consistency.

Thus, for medium-sized earthquakes, the moment magnitude values should be similar to Richter values. That is, a magnitude 5.0 earthquake will be about a 5.0 on both scales.

This scale was based on the physical properties of the earthquake, specifically the seismic moment.

Facebook Comments

Leave a Reply