Seismic Microzonation related to earthquakes, in Delhi and Kolkata
Q. The term microzonation is related to- Published on 23 Feb 16a. Earthquakes
b. Floods
c. Cyclones
d. Droughts
ANSWER: Earthquakes
- The prediction of most of the natural events, particularly the earthquakes, is not possible, but the resulting damage due to them can be minimized by taking proper measures.
- Microzonation is one such measure where the emphasis on the impact of earthquake on the habitat is given.
- It was seen that due to an earthquake in 1985 there was severe damage in Mexico City, though the earthquake source was located about 350 km away from the city. It was realized that putting a large region into a single seismic hazard zone is not a good idea. This and several other examples led to a new concept, called Microzonation.
- Seismic microzonation is a process of identifying such related geological, seismological, hydrological and geotechnical site characteristics in a specific region. These would help design of safe structures to reduce loss of human life.
- Earlier a seismic zoning map for entire India was prepared and published by the Bureau of Indian Standards (BIS), classifying the entire country into 4 major groups Zone-V (High intensity) to Zone-II (Low intensity). These zones encompass wider area for which specific design spectra is commonly used, despite geological and geo-morphological variability within the respective zones.
- Under the microzonation process various investigations viz, ambient noise survey, Multi-Channel Analysis of Surface Waves (MASW) survey, in-situ geotechnical testing, in-situ seismic measurements etc. were carried out and after analysis of data sets different maps viz., Peak Ground Acceleration (PGA), spectral accelerations for different periods, liquefaction potential, predominant frequency, amplification factor, average shear wave velocity at 30 meters depth, geology & geomorphology and projected Hazard Scenarios at GIS platform etc. have now been prepared.
