GUWAHATI, May 4 � Prof Jayanta Pathak of Assam Engineering College (AEC) here, a leading expert of the State in the field of structural and earthquake engineering, has called for urgent steps to make operational the earthquake microzonation outputs of Greater Guwahati areas available with the authorities, through a simplified approach of dissemination.
These outputs were the findings of a nearly six-year-long arduous survey of the seismology-related geo-physical condition of the Guwahati metropolitan region, carried out by a group of national experts.
Talking to this correspondent, Prof Pathak, who was also involved in the above survey as an expert, said that the microzonation outputs should not remain a mere scientific document but an operational document through a peer reviewed process and by converting the �all important hazard information� to a simplified applicable document for use of the policy makers, planners and engineers. Such a step would help a lot in making the future projects � public or private � sustainable, able to withstand disasters.
It needs mention here that the experts engaged in the exercise by the Union Department of Science and Technology at the request of the State Government, mapped five zones and found them to be very high, high, moderate, low and very low hazard regions, where the average Probabilistic Seismic Hazard Index (PSHI) is 0.55, .44, 0.35, 0.26 and 0.16.
The group of experts launched the survey in 2002 and its results were made available to the authorities in January 2008.
Under the study project, an updated seismotectonic map was prepared by the Geological Survey of India (GSI) covering an area of 200-km radius around Guwahati, basing mostly on the data published by the GSI in its 2000 Seismotectonic Atlas of India.
Estimation of the scenario concerning earthquake magnitude from the earthquake catalogue of 140 years was carried out by IIT Kharagpur. Site amplification, classification, strong motion spectral acceleration analysis and synthesis were carried out by IIT Kharagpur, IIT Guwahati, AEC, GSI, India Meteorology Department (IMD) and Regional Research Laboratory (RRL)-Jorhat. A demography and preliminary seismic population risk assessment was carried out by the Jorhat Engineering College (JEC) and IIT Kharagpur.
Earthquake catalogue derived from International Seismological Centre (ISC) and US Geological Survey (USGS) from 1866 to 2006 were used for computing the scenario of earthquake magnitude (SEM) for Guwahati region. The historical earthquakes of 1897 Shillong, 1918 Srimangal, and 1950 Assam were considered in catalogued estimation.
During the survey, simulation for a scenario of earthquake of moment magnitude Mw 8.7, originating from hypocentre of the 1897 Great Assam (Shillong) Earthquake, was carried out to estimate the PGA contour over the metropolitan area.
Inputs from the State�s Directorate of Geology and Mining were also received by the expert group. Its work was collated and guided by renowned expert on Northeast India seismotectonic Dr DR Nandy, Ex-Director, GSI.
Under the project, instrumental site response studies were carried out by the GSI, IMD and RRL-Jorhat to determine the maximum site amplification factors and corresponding peak frequency, covering almost the entire area at 141 locations over Guwahati, along with 200 borehole geotechnical studies by the AEC.
Prof Pathak said most of the data were collected by the experts afresh. For the purpose, they conducted extensive ground survey, including geophysical, geomorphological, land use, land cover, ground noise response spectra, basement configurations and landslide hazard mapping, deployment of strong motion accelerographs, studies on Peak Ground Acceleration (PGA) etc.
The latest revision of the Guwahati Building Byelaw incorporated reference to this microzonation by indicating special provision for buildings in �Natural Hazard-prone Areas.�
But, what is important and need of the hour is to make these microzonation outputs �operational� through a simplified approach of dissemination.
This is specially important for the projects which are geographically distributed � like the water supply projects, sewerage projects and even proposed metro-rail project in the city, said Prof Pathak.
