Lessons to be learnt from Indian quake

Commentary: Even as we were rocked by the aftershocks of Friday's (some say 6.9, other 7.9) and Monday's tremor (5.9 on the Richter scale) and the tragedy of the deaths that resulted, it seems important to look at the impact of the earthquake and examine how technology could have helped before and after the event.

Earthquakes occur every day around the world. Each day there are about 1000 very small (magnitude 1-2) earthquakes on somewhere on the planet (that is about one every 87 seconds). Each year, on average, the Earth experiences 800 earthquakes capable of causing damage (magnitude 5-5.9), and 18 earthquakes of magnitude 7 or larger.

Most earthquakes concentrate at tectonic plate boundaries. However, there is no reliable method of accurately predicting the time, place, and magnitude of an earthquake.

While scientists began recording earthquakes as early as about 1880, it was not until the 1940s that instruments were installed in buildings to measure their response to earthquakes.

The first abundant data on the response of structures came from the devastating 1971 San Fernando, California earthquake, which yielded several dozen records.

Most major earthquakes are heralded by the occurrence of foreshocks, which can be detected by dense local monitoring networks. Other instruments can measure changes in the levels of radon gas, electrical and magnetic properties, velocity changes of seismic waves, and changes in topography.

However, long-term monitoring and examination by these sensors is a requisite as some or all of these factors may change due to the opening of cracks prior to the earthquake.

Today, research is concerned with minimising the risk associated with earthquakes by assessing the combination of seismic hazard and the vulnerability of a given area. Many seismic countries, however, have research programs based on identifying possible precursors to major earthquakes. This includes the study of dilatancy, how rocks crack and expand under the increased stress associated with the earthquake.

According to a paper on earthquake prediction presented by Ruth Ludwin of the University of Washington, individual earthquakes cannot be predicted. However, the world's largest earthquakes do have a clear spatial pattern, and 'forecasts' of the locations and magnitudes of some future large earthquakes can be made.

For example, earthquakes around the Pacific Rim are normal and expected. The long fault zones that ring the Pacific are subdivided by geologic irregularities into smaller fault segments, which rupture individually. Also, the Atlantic Ocean is growing wider each year, thus shrinking the Pacific and pushing the ocean floor beneath Pacific Rim continents.

Geologically, earthquake magnitude and timing are controlled by the size of a fault segment, the stiffness of the rocks, and the amount of accumulated stress. Despite this knowledge, forecasting techniques can only be used for well-understood faults, such as the San Andreas.

It may never be possible to predict the exact time when a damaging earthquake will occur, because when enough strain has built up, a fault may become inherently unstable, and any small background earthquake may or may not continue rupturing and turn into a large earthquake.

It may eventually be possible to accurately diagnose the strain state of faults, but the precise timing of large events may continue to elude us. Efforts will, instead, be channelled into hazard mitigation.

While advances in IT, such as disaster and risk management systems, peer-to-peer networking and massively parallel processing, promise to increase the pace with which this can be done, each of us perhaps should have a hard look at the place that we call home. Is the building we stay in designed to withstand an earthquake?

Earthquakes don't lead to death. Falling buildings do.

Buildings are built to withstand the downward pull of gravity. For most people in India who felt tremors of the recent Gujarat earthquake, it seemed that the building was "being pushed" in all directions, but most of all, sideways.

Newer buildings in Mumbai and across the country are supposed to be made of RCC (Reinforced Cement Concrete) which is expected to help them withstand earthquakes of relatively moderate intensity. Here too, unscrupulous contractors have known to have used a watered down version of RCC which is ineffective.

A safe building is one that can withstand that sideways push, and it is built on a firm foundation. Before designing structures that can withstand earthquakes, engineers and architects must understand the stresses caused by shaking, as this US Geological Survey explains.

Take me to Pt II/ Quake must shake up our confidence

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