Soil liquefaction, a hazard during quakes

By Our Science Correspondent

BANGALORE, JUNE 15. Liquefaction of the underlying soil during an earthquake, which was widespread in Gujarat during the recent quake, poses an additional hazard to buildings and other man-made structures, suggests a paper in the latest issue of the journal, Current Science.

In the wake of the Bhuj earthquake, the largest and the most destructive to have occurred in independent India, ``understanding the nature of liquefaction features and their spatial distribution has important implications for earthquake hazard assessment in similar tectonic and geologic environments'', according to the paper written by Dr. Kusala Rajendran and Dr. C.P. Rajendran of the Centre for Earth Science Studies in Thiruvananthapuram along with Dr. Mahesh Thakkar of R.R. Lalan College at Bhuj and Dr. Martitia P. Tuttle of M. Tuttle & Associates of the U.S.

During an earthquake, vulnerable soil layers can liquefy. Much of the ground failure during the Bhuj earthquake was caused by ``lateral spreading'' when liquefied soil or intact blocks riding on it flowed down a gentle slope. Such lateral spreading often led to failure of engineered structures, the paper says.

The potential for liquefaction during an earthquake depended on a variety of factors such as the slope of the land, depth of the water table, thickness of the top soil and availability of a liquefiable soil layer below, Dr. Rajendran told The Hindu. Liquefaction susceptibility maps were an important component of the U.S. Geological Survey's earthquake hazard studies, he pointed out.

According to the paper, a ``hidden fault'' located north of the Kutch mainland fault appeared to have generated the earthquake. A fault is a fracture left by a past earthquake. Earthquakes are more likely to occur at an active fault. Geologists identify faults by the surface features.

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