Centre to map faultlines to protect quake-prone

“The microzonation of Delhi is complete and we are going to present it to the Chief Minister (Sheila Dikshit)… It is a complete map of the region showing the possible ground movement during earthquakes,” Science and Technology Minister Kapil Sibal said.

The minister said he planned to extensively map “high-risk areas including Jammu and Kashmir”, adding: “Since the exercise is of large magnitude we are planning to outsource it.”

Seismic microzonation involves recording the response of soil layers and variation of ground movement in areas where quakes have occurred. It yields a separate map showing the effect earthquakes might have on different areas, which are classified as low, middle and high intensity zones.

“The zones are classified on the nature of the soil. If the soil is soft the structures on it will collapse and it the soil is rock filled the structures will not fall. So microzonation classifies areas in the city on the basis of the earthquake hazard,” Sibal said.

After microzonation is done, states can change their building by-laws and protect buildings from the effects of earthquakes.

“In case the buildings are already on the area, people can be advised to strengthen them,” he added.

The area within 200 km of the Himalayan faultline mostly falls in zones IV and V, which are high-damage risk zones with high seismic activity.

Srinagar and some parts of the Valley are in Zone V where seismic intensity can be as high as 10 on the Richter scale. The rest of Jammu and Kashmir as well as Himachal Pradesh, Delhi and Punjab are in Zone IV, where seismic activity can go up to 9.0.

The areas are at risk from what international experts term the “potential Great Himalayan Quake”. Earthquake activity in the region is caused by a collision between the Indian plate and Eurasian plate.

Seismic microzonation is done using ground motion recorders. The main indicators are soil layer thickness, natural ground frequency, shearwave velocity and amplication factor. The Delhi study assessed possible amplification at various locations.

Signals at a few select locations were used as a model as it was not possible to install ground motion recorders at all places in Delhi.

Sibal said the use of “electronic devices” would provide faster and more accurate information about the magnitude of earthquakes and eliminate confusion between Indian and international quake measurements. “Since we take about an hour to accurately measure the intensity that’s why the US Geological Survey can do accurate measurements before us,” he added. The minister said electronic network stations — earthquake measuring centres — would be installed across the country to make sure quake measurement is accurate.

Ten such stations are coming up in Delhi this month; all of India will be covered in a year.