There are two numbers generally measured, whenever an earthquake occurs - its magnitude and intensity. While magnitude is termed as the strength of the earthquake, the intensity of the natural calamity varies from place to place, depending upon a number of factors. Two scientists are associated with the invention of the scales for the measurement of each of the two numbers - Charles F Richter and Giuseppe Mercalli. In the following lines, we have examined the two terms — magnitude and intensity — in detail, and provided information on how they are measured.
Measuring Magnitude & Intensity Of Earthquakes
In 1935, an American seismologist, Charles F Richter, made use of a logarithmic scale to measure the magnitude (the size and strength) of an earthquake. Known as Richter scale, it was based on the amplitude of the waves, measured by a seismograph. When the magnitude is measured, it is adjusted to account for the distance between the seismograph and the epicenter of the quake. The numbers shown by Mercalli scale vary according to the destruction caused by an earthquake at each level.
The magnitude of an earthquake is recorded in the ascending order of destruction, starting from I to XII. When the scale measures I as the magnitude, the earthquake is considered to have the slightest effect on buildings and human beings. On the other extreme, the calamity with a magnitude of XII is regarded as severely destructive. Significant damage to buildings can occur when the magnitude of earthquake is VII and above.
Italian scientist Giuseppe Mercalli invented Mercalli scale in 1902. It is used to measure the intensity of an earthquake, based upon the observation of destruction caused by the calamity at a particular location. The intensity may vary from place to place. The distance from the epicenter, design and quality of construction of local building and the type of surface beneath the buildings are the factors responsible for the variation of intensity of an earthquake from one place to the other.
The seismographs near the epicenter of the earthquake measure its intensity, ranging from 1 to 9. The lowest intensity, number 1, is not felt at the surface. Little damage is caused, when the intensity is recorded as 4. The number 6 corresponds to a strong earthquake, clearly felt over a wide area. The intensity of earthquake, noted as 7 and 8 on the Richter scale, is considered as highly destructive, damaging the buildings and life up to 100 km from epicenter. The intensity of 9 has not been recorded till date. Such a high intensity is regarded as an earthquake that can devastate life up to 1000 km from the epicenter.