Union Government released Seismic Microzonation reports for Delhi and Kolkata

The Union Minister for Science and Technology and Earth Sciences Dr. Harsh Vardhan released the Seismic microzonation reports for Delhi and Kolkata in New Delhi on 22 February 2016.

It will help in minimizing the effects of earthquakes by assessing Seismic Hazards, by implementing safe building construction codes, and adopting appropriate land-use planning.

The integrated seismic hazard map based on microzonation for Delhi was prepared by the Earthquake Risk Evaluation Center (under the IMD), now merged with National Centre for Seismology, Union Ministry of Earth Sciences.

On the other hand, the seismic microzonation project for the city of Kolkata was conceived by Indian Institute of Technology Kharagpur in consortium with a few other organizations in Kolkata under the aegis of the Geosciences Division, Union Ministry of Earth Sciences.

What, Why and How of Seismic microzonation?

It is a process of identifying geological, seismological, hydrological and geotechnical site characteristics in a specific region.  These would help design of safe structures to reduce loss of human life.

Under this process various investigations which are 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.

They include Peak Ground Acceleration (PGA), spectral accelerations for different periods, liquefaction potential, predominant frequency, amplification factor, average shear wave velocity at 30 meters depth, geology and geomorphology and projected Hazard Scenarios at GIS platform etc. are prepared.

The need for the microzonation arose after the Mexico earthquake in 1985 which caused 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.

Beneficiaries of seismic microzonation maps of Delhi and Kolkata

• Disaster Mitigation and Management Authorities

• Urban Development Authorities

• Planning, Design & Construction Agencies

• Risk Assessment to existing life & Property

• Defense Installations

• Heavy Industry

• Public Utilities and Services

Present Classification of Seismic Zones in India

The Bureau of Indian Standards (BIS) classifies and publishes seismic zoning map for entire India. It classified India into 4 major groups which are:

    Zone - II: This is said to be the least active seismic zone.

    Zone - III: It is included in the moderate seismic zone.

    Zone - IV: This is considered to be the high seismic zone.

    Zone - V: It is the highest seismic zone.

India into earthquake hazard zones does not use Zone 1. No area of India is classified as Zone 1.

National Capital Territory (NCT) Delhi is located in Seismic zone IV, whereas Kolkata is placed at the border of Seismic Zone III and IV.

The presence of these two cities in high intensity seismic zones necessitated systematic assessment of seismic hazard, vulnerability and risk.  Unplanned urbanization defying building codes are continuously increasing the earthquake vulnerability of Delhi and Kolkata.

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