Measure of the Magnitude of an Earthquake
Apowerful earthquake of magnitude 7.5 struck Western Japan on January 1st, 2024.
What does ‘magnitude 7.5’ mean? Earthquakes are sudden movements inside the earth, where tectonic plates move against each other, which leads to the release of energy. Over time, this energy becomes more than the earth can withstand and is released as an earthquake.
Magnitude is the size of the earthquake. This can be determined through the data obtained through a seismometer, which is an instrument that responds to ground noises and shaking.
The timing and recording devices within it provide a seismograph through which the following information can be obtained.
The time of the earthquake
The epicenter – which is the location on the surface of the earth of its occurring.
The depth at which the earthquake
occurred.
The amount of energy released by
the quake.
There are a number of ways of measuring the magnitude of an earthquake.
In 1932, American Charles Richter devised the Àrst method for measuring earthquake size, which is known as the Richter Scale. The formula to obtain the Richter magnitude ‘M’ is
M = Log (A/A’) where A is the amplitude of the earthquake and A’ is the amplitude of a standard earthquake with a magnitude of 0.
The energy released ‘E’ in joules can be found using the equation
Log E = 4.4 + 1.5 M
However, the Richter Scale tends to underestimate the size of large earthquakes. This has led to the development of the Moment Magnitude Scale, which is widely used nowadays. This scale was developed by Hiroo Kanamori of Japan and Thomas Hanks of USA in the late 1970s.
Given below is a general guideline about the magnitude of earthquakes and its effects.