What is the intensity of Erthquake?
Feel the Structure, MSA!
Latest Earthqauke(Epicentre at Nepal) datd on Nov9, 2022 which resulted huge tremors in delhi-ncr indulged me to write something important to measure volume of destruction in terms of intensity or magnitude.
Intensity: Intensity of an earthquake is the amount of shaking felt by an observer during earthquake. It is measured by MSK Intensity Scale which is indicated from I to XII(Ref: IS-1893-2016).
The intensity scale is basically a qualitative or perceptive scale developed based on degree of destructiveness, or human perception of the degree of shaking.
However, earthquake is measured by intensity but it is not the true method to measure an earthquake because at the same distance from epicentre, two building will be shaking differently due to its geometrical arrangement. Hence, truly earthquake is measured by Magnitude. Magnitude is shown in Ritcher Scale which is the amount of energy released during earthquake and it is constant. For two distant places from epicentre, however intensity will be different but magnitude will be the same.
We can corelate similarity of lighted buld with intensity of earthqauke. Take an example of reading a book near an electric bulb and far away from this bulb. It is easy to read something near the bulb but it is difficult to read the same book when we become distant from it. However, energy released per hour from this bulb is same but intensity of light gets reduced when we start keep away from this. In the same way, during earthquake event, amount of energy released will be same but it’s intensity will be reduced when we keep away from away it. People near epicentre ( Origin of Earthqauke) will feel heavy jolting whereas people away from epicentre will feel less tremors.
Also, two or more than two buildings at the same distance from the epicentre will be damaged differently. One building may not have undergone even any crack whereas other building at same site can be heavily damaged. The above damaged comes under the effect of geometrical arrangement of columns, beams, walls, shear wall etc.
Hence, for the two buildings at the same site, magnitude will be same but intensity will be different due to geometrical arrangement (Either stable or untable geometrical arrangement ). One building with ill designed ignoring earthquake parameters, any observer inside this building will feel heavy jolting /tremors while other observer at other building at the same site will feel less tremors as building has been designed considering all earthqauke parameters.