EARTHQUAKE: Ground beneath our feet
THE EARTHQUAKE which rolled over much of the subcontinent on Friday is yet another grim reminder of man’s vulnerability in the face of natural disasters. Probably triggered off by the collision of massive geological plates an indeterminate distance below the earth’s surface, the tremors lasted 50-odd seconds — long enough to kill and maim, topple buildings, disrupt electricity and water supply systems, and throw communications networks out of gear.
And when the earth fell still, Bhuj — where the epicentre fell — and surrounding regions had been transformed from bustling cities into dust-shrouded wasteland. The dazed populace that survived must feel all the more frightened since the earth chose to convulse at this time and not during summer when many people sleep out in the open at night.
The actual dimensions of the tragedy are yet to be established since the authorities probably did not expect a quake of this proportion — of almost 7.9 on the Richter scale, according to some reports — to occur. The scale, named after the US seismologist, Charles Richter, who devised it in 1935, is logarithmic. This means that each step up the scale represents a ten-fold increase in the amplitude of the energy waves emitted by the quake. It starts with terrestrial tremors detectable only by instruments (Magnitude 1), through those detectable within 20 miles of the epicentre (Magnitude 4-5) and moderately destructive Magnitude 6 convulsions, to major quakes of Magnitudes 7 and 8.
The earth is made of continental plates which, in turn, comprise sub-plates. Their continuous movement leads to friction as they rub together along the rifts and valleys of weak zones that run miles deep into the earth.
Usually major faults that have been active for a very long time show large displacements of the crust. Thus sections of the crust either side of the San Andreas fault in California have slid past one another by several hundreds of miles over the last five million years. The exact movements and chronology of plate tectonic forces have yet to be studied in detail, which is why it is still rather difficult to predict the exact place and time of a likely tremor.
But the good news is that it may not be long before observation satellites monitor the earth’s atmosphere and make quake prediction more of an exact science. For instance, tell-tale changes occur in the ionosphere before earthquakes in the form of release of gases and electrically charged particles, as well as minor fluctuations in the planet’s magnetic field. These can be detected by orbiting satellites and relayed back to earth stations where scientists can use the data to find out when and where the earth is going to shiver next.
Seismologists at the National Geophysical Research Institute in Hyderabad now wryly confess that they are hardly surprised by the disaster since they had all along been aware of the region’s major rift zone status. This raises the poser as to why then the local people were not enlightened early enough about the dangerous, if quiescent, lie of their land.
It is high time the authorities addressed the all-important question of earthquake education. It is one thing to talk about ‘disaster management’ and quite another to actually practise it. Thus, people should be taught to observe natural phenomena like sudden changes in water levels in wells and behavioural changes in animals and birds which precede quakes. More importantly, the do’s and don’ts to be observed during and after a quake should be properly communicated to the public, so that losses are much reduced.
‘Rift zones’ include much of the world’s population — if the first ever global earthquake map is anything to go by. The document, painstakingly prepared by an international team of scientists over a decade and released last year, details the entire planet’s quake hazard zones. And there are few surprises in it: southern California, southeastern Hawaii, Turkey, Taiwan, Iceland and the India-China border are most likely to experience strong shaking in the future.
It is significant that one of the greatest hazard areas in the map, coloured a deep red, is along the India-China border, where India is literally slamming into Asia producing the still growing Himalayas. So quakes in the Himalayan range are probably due to India being pushed into China. As for the rest of the country, and the brittle peninsular area, the earth’s heaving must be the result of landmasses scraping against each other along the rift zones.
It would not be a bad idea for people in this part of the world to use such maps for updating and establishing building codes. The Bureau of Indian Standards could learn a thing or two from quake-prone Greece. Decades of progressively stricter building codes there allowed the huge Athens metropolis to ride out the September, 1999 earthquake (which measured 6.1 Richter) with much less misery than did western Turkey, where shoddy construction was blamed for near total destruction in many places during the August, 1999 tremors.
Indian agencies should vastly augment its criteria for quake-resistant building designs for the country’s different quake-prone zones and make it mandatory for real estate agents and potential buyers to comply with those guidelines.
The entire country has been divided into five zones based on the soil quality and the intensity of quakes they may experience. Take Delhi, which falls in Zone Four in this index. The metropolis and surrounding areas experience more than 20 quakes of magnitude 2 each year, and the potential epicentre for a ‘big one’ actually lies plumb on Shakti Sthal — a disturbing thought, especially for those living in the densely populated trans-Yamuna colonies.
The intensity of damage in an area depends on the quality of soil. Thus the least damage will be in places where the soil is rocky, while a region with loose soil is most likely to be worst hit by an earthquake. The trans-Yamuna colonies are almost entirely built on loose soil. Every year the earth quakes more than 30,000 times although, fortunately, the intensity is not all that great most of the time, and by fortuitous coincidences unpopulated areas tend to be targeted.
But there is no hard and fast rule as last Friday so