What is the difference between Intensity and Magnitude?
Earthquake Intensity is measured in Modified Mercalli Scale. It is a descriptive scale to measure severity of earthquake shaking. Mercalli scale tells the effects of quake on the Earth's surface, objects, human made structures, nature, and humans. It is measured on a scale from I (Not felt) to XII (complete destruction). Below here the description of each scale.
|I. Not felt||Not felt by everyone except by a very few people under especially favorable conditions.||II. Weak||Felt only by a people resting at that time. Generally felt on upper floors of the buildings.||III. Weak||Noticeably felt by people inside the buildings, especially on upper floors of the buildings. But most people do not realize it as an earthquake. Standing vehicles move rock slightly. It might vibrate something like the passing of a truck.||IV. Light||Felt by many people indoors, few people outdoors will fell during day time. The Dishes, windows, doors will make some sound and walls make cracking sound. People might feel sensation like heavy truck striking the building.||V. Moderate||everyone will feel the earthquake. Many will awaken in the night, Might break windows, over turn unstable objects, Pendulum clocks might stop.||VI. Strong||Felt by everyone, many frightened. Might move heavy furniture's, wall plaster fallen, slight damage to building structures.||VII. Very Strong||No damage to buildings built with good design and construction; minor to moderate damage to well-built ordinary building structures; significant damage in poorly built or badly designed buildings.||VIII. Severe||minor to moderate to buildings built with good design and construction; significant damage to well-built ordinary building structures; major damage in poorly built or badly designed buildings. Fall of monuments, walls, factory stacks||IX. Violent||Damage considerable in specially designed structures; well-designed frame structures thrown out of plumb. Damage great in substantial buildings, with partial collapse. Buildings shifted off foundations.||X. Extreme||Some well-built wooden structures destroyed; most masonry and frame structures destroyed with foundations. Rails bent.||XI. Extreme||Few, if any, (masonry) structures remain standing. Bridges destroyed. Broad fissures in ground. Underground pipe lines completely out of service. Earth slumps and land slips in soft ground. Rails bent greatly.||XII. Extreme Damage total.||Waves seen on ground surfaces. Lines of sight and level distorted. Objects thrown upward into the air.|
Magnitude of earthquake measures the quantity of seismic energy released by quake at its source. It is measured by Richter Magnitude Scale. It is given in single numerical value on Richter scale. But the intensity is based on area affected, with high intensity near the epicenter and lower further away from the center. The Richter scale is a base-10 logarithmic scale and was developed in 1930s. Below here is the range of Richter scale based on intensity of earthquakes
|less 2.0||Micro||I||These are Microearthquakes. Not felt by everyone. Can be recorded by seismographs.|
|2.0 - 2.9||Minor||I to II||Felt lightly by few people. No damage to structures and buildings.|
|3.0 - 3.9||Often||II to IV||Felt by many people, but does not causes any damage. Not noticeable shaking of indoor objects.|
|4.0 - 4.9||Light||IV to VI||Indoor objects can shake and can hear some rattling noises. Felt outdoor. No significant damage|
|5.0 - 5.9||Moderate||VI to VIII||Felt by everyone.damage to poorly constructed structure and builds. Can cause damage of varying severity to poorly constructed buildings.|
|6.0 - 6.9||Strong||VII to X||Strong quake and felt by everyone. Can damage any building and only earthquake resistant building can survive.|
|7.0 - 7.9||Major||VIII or greater||Can be felt to long distance from epicenter. Most structure can damage.|
|8.0 - 8.9||Great||Great damage to structures and buildings. Felt in entire region and can trigger tsunami.|
|9.0 and greater||Total destruction||Heavy destruction and can change ground topography completely. can also shift earth pole by few degrees.|
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