Micro-zonation earthquake map for Vijayawada city

Syed Akbar

Hyderabad: The Geological Survey of India is now busy preparing seismic hazard microzonation maps of Vijayawada to prevent loss to life and property in case an earthquake hits the city. Vijayawada is the only major place in Andhra Pradesh that falls under earthquake zone III. The rest of the State falls under seismic zone II, which is relatively safer.

Once the microzonation maps are ready, the Earthquake Geology Division of GSI will advise the municipal corporation about the areas in the city vulnerable to earthquake hazard, particularly high-rise buildings

The Vijayawada urban agglomeration has a population of over 17 lakh and as many as 22 seismic sources, mainly faults, in and around the city have been identified. The Gundlakamma fault is the major active fault in the vicinity.

The city has four types of soil with black cotton soils making up 58 per cent, sandy clay loams 23 per cent, red loamy soils 17 per cent and sandy soils 2 per cent. The microzonation maps to be prepared on a scale of 1: 10,000 to 5,000 metres will be useful for disaster management. Similar studies are proposed for other seismic areas like Ongole and Bhadrachalam.

As part of the seismic microzonation, the city is divided into subregions in which different safeguards must be utilised to reduce, and / or prevent damage, loss of life and societal disruptions during future earthquakes. The maps will also help to mitigate the effects of an earthquake by quickly determining source parameters and acquiring information about local geology and soil profile, topography, depth of

water table, characteristics of strong ground motions and their interaction with man-made structures.

According to senior geologist Prof SK Nath, earthquake disasters are inevitable but it is possible to minimise the aftermath of an earthquake if the zones that are more susceptible to undergo maximum ground motion are identified. Seismic microzonation helps in case of seismic hazards as it gives a realistic answer in terms of ground motion at a higher resolution.

Based on the earthquake maps, the city civic body may come out with specific design of buildings and structures, assess seismic risk to the existing structures and constructions, and guidelines on management of land use.