What is Richter Scale?
The Richter scale was invented in the 1930s by Dr. Charles Ritcher, a seismologist at the California Institute of Technology. It is a measure of the largest seismic wave recorded on a particular kind of seismograph located 100 km from the epicenter. The wave height is measured by seismograph (type of pendulum with an ink pen or digital recorder) and the output is called seismograms.
As the measurement is based on logarithmic scale, a wave 1 mm (1000 microns) high on a seismogram has magnitude of 3 (because log(1000) =3). Similarly, a wave10 millimeters high would have a magnitude of 4. For reasons that a factor of 10 change in the wave height corresponds to a factor of 32 change in the amount of energy released during the earthquake, magnitude 7 earthquake produces waves
10 x 10 = 100 times as high and release energy 32 x 32
= 1024 times as great as a magnitude 5 earthquake.
Therefore in general sense, an earthquake of 8 RS is not twice as strong as the 4 RS earthquake but many thousand times stronger than 4.