Deccan Chronicle        13.01.2011

1 in 3 Chennai buildings vulnerable to earthquake

January 13th, 2011

Jan. 12: Are you one of the residents staying in a huge apartment complex? Do you know that about 30 per cent of multi-storeyed buildings in the city are vulnerable to earthquakes of even small magnitude?

Chennai has been placed in Zone 3 category among cities vulnerable to earthquakes by the Bureau of Indian Standards since 2001. This means that the city is most vulnerable to moderate earthquakes at any point of time.

“Most buildings in the city, constructed prior to 2001, do not meet the parameters prescribed for Zone 3 areas. So, even relatively moderate earthquakes could cause huge disasters,” warns prof S. Rajarathnam, director of centre for disaster mitigation and management (CDMM), Anna University.

The centre, in association with various government bodies, has been surveying the entire city. “We employed rapid visual screening method to quickly assess the buildings in the city. Our findings are disturbing because of the inherent weakness of a number of buildings,” explains prof Rajarathnam.

However, if anyone in the public is interested in assessing the quake resistance of their buildings, the centre is willing to undertake an inspection. Prof A.R. Santha Kumar, consultant to CDMM and former dean of Anna University, said a team of experts has examined all government buildings in Chennai and remedial measures have been recommended. “We have also completed the screening of all buildings with more than four floors,” he said.

The centre is also in the process of making a Geographical Information System (GIS)-based map on vulnerability assessment of disasters in Chennai with the help of government agencies. “We will be ready with such a map in the next 18 months. The map will outline life-saving techniques such as possible escape routes and shelter areas associated with all buildings in the eventuality of an earthquake,” he said.

The Hindu         13.01.2011

29% of buildings in Chennai vulnerable to quake: survey

Special Correspondent

A survey to assess seismic vulnerability of the built environment in Chennai has classified 29 per cent of the buildings in the city as highly vulnerable in an earthquake event.

The survey undertaken by the Centre for Disaster Mitigation and Management (CDMM) at Anna University aerially mapped 22,758 medium-to-tall buildings in the city deploying the Rapid Visual Screening technique.

The surveyed buildings included 11,224 three-storeyed structures, 7,500 four-storeyed buildings and 2,053 buildings with five floors or more.

Launched as part of a Government of India-funded project to evolve a GIS information based e-governance model for vulnerability assessment of Chennai, the study also recommended “ground truth” (physical) verification of select buildings to confirm the extent of vulnerability.

The study that also analysed soil types in the city found that the clay and unconsolidated sediments were likely to cause higher local site amplification of earthquake energy effects.

Such amplification areas were identified at Vyasarpadi, Siruvallur, Otteri, Purasawalkam , Vepery, Egmore, Kolathur, Villivakkam, Anna Nagar, Aynavaram, Koyambedu, Arumbakkam, Kodambakkam, parts of T. Nagar, Taramani and parts of Velachery.

Recommendation

The soil liquefiable areas were mapped in Vyasarpadi, Purusawakkam, Koyambedu, Villivakkam, Saligramam, T. Nagar and West Mambalam. The study recommended soil improvement in these areas for mitigation of seismic damage.

Buildings coming up in future could also incorporate the amplification factor to realistically design appropriate earthquake resistant features relevant to the varying levels of seismic hazards across the city instead of uniformly following the coefficient for Seismic Zone III, the study has recommended.

It is pointed out that while Chennai was re-designated from Hazard II zone to Hazard III zone in 2001, several buildings that came up prior to that year remain ill-designed to withstand earthquake events. “As a result, even relatively moderate earthquake events can be the source of huge socio-economic impact,” said S. Rajarathnam, Director, CDMM, Anna University.

While the draft seismic hazard map for the city is ready from the perspective of borehole data analysis and engineering seismograph survey, the GIS-based e-governance model will be put together after gathering inputs from various user departments, said A. R. Santhakumar, CDMM consultant.

Surveyed buildings also include 11,224 three-storeyed structures, 7,500 four-storeyed buildings