Safe as houses

Earthquakes don't kill; badly built houses do. This time-tested observation becomes a clich every time a quake does damage in India and loses currency equally quickly from public memory. Already, lessons of the massive January 26 quake that ravaged Gujarat are getting out of fashion. But, quakes are nothing new to India -- 55 per cent of the country is prone to seismic activity. Several regions in the country that are earthquake prone have traditionally built houses that minimise the damage to life and property and stand up well when earth becomes fluid momentarily. These techniques are based on traditional materials and good old-fashioned, common sense architecture. While materials that have been used to build such houses -- timber and bamboo, for example -- are not as readily available now as they were in the past, the common sense isn't that difficult to find, fortunately. The wisdom and attention to detail can be applied to modern materials as well. Shraddha Navalli profiles the architectural axioms that make the difference between life and death in quake-prone areas

No House is quake proof
No building is entirely free of damage during a quake. Notwithstanding that, all houses, big or small, can be made safer. Structures can be made to withstand earthquakes of a particular magnitude by taking certain precautions. Buildings collapse as a result of inertial forces. During an earthquake, the lower part of a building tends to vibrate as it is in direct contact with the ground. The forces of inertia, however, keep the upper portions static. This conflict of forces leads to collapse.

The magnitude of these forces is directly proportional to the weight of the building -- the heavier the structure, the greater is the damage. If the structure is light, people are less likely to die in case of a collapse. Avoiding compression structures like domes, vaults and arches is another option, says Delhi-based architect Arunav Das Gupta, professor at Tulsi Vidya Bharati School of Habitat Studies. Why? Because the property of compression structures is to distribute the load of the building through compression to the base of the structure, increasing the probability of the building's collapse. The structural system needs to be tensile and the material should be flexible, as is the case with timber, steel and bamboo. It also helps if the structure is constructed in a way that it vibrates as one unit and sways together. Traditional constructions in India's Northeast follow this principle.

The strength of the masonry depends upon the strength of mortar. The 1993 Latur earthquake took such a heavy toll as huge stone masonry walls, very common in the area, gave way. The walls and roofs were heavy, the mud mortar was weak and could not provide enough cohesion to sustain the walls.