Explain in detail how the Richter scale and the modified Mercalli intensity scale are different. The Richter and modified Mercalli scale are very different in many ways. The Modified Mercalli Scale (MMS) gives an indication of the intensity of an earthquake while the Richter scale refers to its magnitude.
Seismologists use a Magnitude scale to express the seismic energy released by each earthquake. Here are the typical effects of earthquakes in various magnitude ranges. Seismology a scale of seismic intensity is a way of measuring or rating the effects of an earthquake at different sites. The Modified Mercalli Intensity Scale is commonly used in the United States by seismologists seeking information on the severity of earthquake effects. Intensity ratings are expressed as Roman numerals between I at the low end and XII at the high end.
The Richter scale is the best-known scale for measuring the magnitude of earthquakes. The magnitude value is proportional to the logarithm of the amplitude of the strongest wave during an earthquake. A recording of 7, for example, indicates a disturbance with ground motion 10 times as large as a recording of 6. The energy released by an earthquake increases by a factor of 30 for every unit increase in the Richter scale. The table below gives the frequency of earthquakes and the effects of the earthquakes based on this scale.
The intensity of an earthquake at a particular locality is a measure of the violence of earth motion produced there by the earthquake. It is determined from reported effects of the tremor on human beings, furniture, buildings, geological structure etc. Unlike the magnitude, which has a unique value for a particular earthquake, the intensity of an earthquake at a place depends on the distance of that place from the epicenter, the depth of the focus, the intervening and local earth structures and the type of fault motion that caused the earthquake.