The Richter Scale And Modified Mercalli Scale
The Richter Scale was invented by an American scientist Charles Richter along with a fellow colleague Beno Gutenberg, both of the California Institute of Technology in 1935 to compare the size of earthquakes. It measures how much the ground shakes 60 miles from the earthquake’s epicenter. This measuring scale not a physical measuring instrument but a mathematical formula.
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. Each unit on this scale is equivalent to a power factor of about 32. That means, a reading of 5 on the Richter Scale is 32 times more powerful than a 4.
Another scale of earthquake measurement is called the Mercalli scale, invented by Giuseppe Mercalli in 1902. This scale estimates the severity of the quake based on the observations of the people who have experienced the earthquake.
| Mercalli Intensity | Richter Scale Magnitude | Witness Observations |
| I Feeble | 1 to 2 | Felt by very few people; barely noticeable. |
| II Slight | 2 to 3 | Felt by a few people, especially on upper floors. |
| III Moderate | 3 to 4 | Noticeable indoors, especially on upperfloors, but may not be recognized as an earthquake. |
| IV Moderate | 4.3 | Felt by many indoors, few outdoors. May feel like heavy truck passing by. |
| V Rather Strong | 4.4 - 4.8 | Felt by almost everyone, some people awakened. Small objects moved. Trees and poles may shake. |
| VI Strong | 4.9 - 5.4 | Felt by everyone. Difficult to stand. Some heavy furniture moved, some plaster falls. Chimneys may be slightly damaged. |
| VII Very Strong | 5.5 - 6.1 | Slight to moderate damage in well built, ordinary structures. Considerable damage to poorly built structures. Some walls may fall. |
| VIII Destructive | 6.2 - 6.5 | Little damage in specially built structures. Considerable damage to ordinary buildings, severe damage to poorly built structures. Some walls collapse. |
| IX Ruinous | 6.6 - 6.9 | Considerable damage to specially built structures, buildings shifted off foundations. Ground cracked noticeably. Wholesale destruction. Landslides. |
| X Disastrous | 7.0 - 7.3 | Most masonry and frame structures and their foundations destroyed. Ground badly cracked. Landslides. Wholesale destruction. |
| XI Very Disastrous | 7.4 - 8.1 | Total damage. Few, if any, structures standing. Bridges destroyed. Wide cracks in ground. Waves seen on ground. |
| XII Catastrophic | > 8.1 | Total damage. Waves seen on ground. Objects thrown up into air. |
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