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Questions from the Quetta quake
Anniversaries of calamities make us revisit the ways and means in which we may avoid mistakes made in the past. We should learn from history, though this doesn’t happen often enough.
One of the most destructive earthquakes in Pakistani history, having a magnitude of 7.5, hit Quetta on May 31, 1935. About 50,000 people perished as a result. The maximum intensity of the seismic event on MM scale was IX.
Just 16 months earlier — on Jan 14, 1934, to be exact — an earthquake of magnitude 8.25 had hit the Bihar-Nepal border region, killing about 30,000 people.
Following the Quetta quake, a field survey was undertaken by W.D. West, who wrote a scholastic and scientific report on it. The British government, which then ruled over the areas now constituting Pakistan and India, was shaken by the earthquake and certain corrective and remedial steps were formulated.
Had some of these recommendations been adopted for implementation, the damage taking place in subsequent earthquakes would have been reduced greatly. After the Balochistan earthquake, for instance, army engineers developed a simple technique known as “Quetta Bond” for aseismic designing of buildings.
If this technique had been used widely in the rural areas of Pakistan, the death toll in the Oct 8, 2005, calamity would not have been as high as it unfortunately was. It is felt that the latent and invisible seismic umbra and penumbra should never be forgotten.
After observing the destruction caused by many earthquakes in several seismically active countries, it is felt that disaster may be mitigated to a sufficient degree by a double-edged tool:
— proper aseismic designing of houses, and;
— timely precursory warning.
It has been observed in most of the seismically active countries that the authorities rarely remind people about the desirability of aseismic designing of new houses and the importance of strengthening existing buildings. It is the owner himself or herself who has to take initiatives in this regard.
Interestingly, the measures required are not expensive. On an average, the cost of designing a new house aseismically or strengthening an old house is about 5 to 7 per cent of the total cost of construction. Spending a small amount towards making a house earthquake-resistance in the pre-seismic period saves it from collapsing suddenly in the co-seismic period, thereby protecting the lives of people living there.
There are several seismic codes and the relevant details about columns, beams, foundations, walls, doors and windows are available too. These data are technical in nature and need some engineering background to understand and follow.
While constructing a house, the consulting engineer should be told to follow the relevant seismic code. It should be remembered that there is no technology that could make a house hundred per cent quake-proof.
If a house is located right at the epicentre then it is bound to collapse. But the manner in which a properly designed aseismic house collapses is quite different from the way an ordinary one would. An ordinary house, depending on its height, may collapse, say, within five to 15 seconds during an earthquake.
A seismic-resistant house, on the other hand, will collapse slowly or gradually. It may take anything from 50 to 100 seconds to collapse completely. As a consequence, the people living there may come out before the house collapses. The slow collapse is due in great measure to the ductility of the structure.
A question that is often put to engineers and scientists is: what to do with the existing non-aseismic buildings? Well, there are several simple methods that could be adopted easily. These are affordable as well as inexpensive:
Cross bracing — This is mostly applicable to non-RCC type structures or two-storey houses. Install two rods of steel of 5mms to 8mms diameter in two diagonal directions on the wall. The two ends of the diagonal rods may be bent in a ‘U’ shape.
These ends may be fixed with the existing rods of the columns. If there is no reinforcement then it could be embedded in the wall. After fixing the rod, plaster it with mortar. If the house is a non-RCC one, then fix the rods in the masonry.
If the structure is weak then such diagonal fixing could be both inside and outside the wall. If the house is a single-storey and Kutcha type, then instead of steel, bamboo could be used.
Seismic belt — Take a grill or stretched wire grill (used for compound fencing) of about 50cms width and fix it at the lintel level on the house in a belt-like fashion. The grill may be fixed with nails or nuts and bolts at an interval of about 50cms. Such a step reduces the amplitude of vibration of the house and makes it safer during seismic shaking.
Apart from the engineering safety of the house, it is necessary to know about the imminent seismic danger in advance. Unfortunately, there are a large number of engineers, scientists, researchers and administrators who are of the confirmed opinion that earthquakes cannot be predicted. This assumption has retarded the growth and development of prediction techniques.
This is wrong from the epistemological point of view. As a result, in most countries earthquake disaster mitigation is almost equated to salvaging the post-seismic situation. No mitigation expert is prepared to listen to theories dealing with earthquake prediction.
From January 2001 to October 2005, three seismic events in India, Indonesia and Pakistan have claimed about 325,000 lives. I have been undertaking research in the field of earthquake and allied subjects for the last three decades. But after observing the above death toll, I feel that my research is of no use because I could not save a single life.
As an administrator engaged in disaster mitigation, to save lives is of utmost priority. It is pertinent that the authorities issue a suitable warning before an earthquake actually strikes. Issuance of prior warning is perhaps the only way to save lives.
If the existing instrumentation is not capable of issuing a warning and a large number of people die during an earthquake, then everybody must be ready to look for a viable alternative. In the absence of a viable scientific or technical alternative, if the barking of a dog or the cawing of a crow gives us some precursory warnings we should accept the same with open hearts.
Let me admit here that until a few years ago, I too was of the view that earthquakes cannot be predicted. However, after seeing the huge death toll and surveying some quake-hit areas I have come to the realisation that we can indeed be forewarned about earthquakes.
Meanwhile, how earthquake watching could be organized at the social level is discussed below:
For this purpose, small Earthquake Monitoring Groups (EMGs) of about ten to 20 persons may be formed at various levels — such as the village, neighbourhood, college and district levels. An EMG may decide to meet once a month or as and when required.
Monitoring of various precursory parameters should be taken up by these groups. The entire operations to be undertaken by the group will not cost a single rupee and yet it is possible to collect the required seismological and geological data.
Let students in schools and colleges measure the magnetic field and the gravity field. They may perform the experiments to get some additional marks in their examinations.
Chief of the physics department or the headmaster/principal will keep a methodical and fortnightly record of magnetic field and gravity field at his institution. Both these parameters undergo observable changes in value before the quake. Keeping records over a reasonable length of time will help monitor these important parameters.
The group may also monitor subsurface temperatures. For this purpose, a pit of 2m to 3m depth is dug up in an enclosed area such as a garage or veranda. A mercury or a metallic thermometer is used to measure the subsurface temperature, possibly twice a day. The first measurement may be taken between 0800 and 1000 hours and the other one from 1500 to 1700 hours.
It is seen that the subsurface temperature rises by 4 to 6 degrees Celsius prior to the quake. The rise in temperature is not sudden. It starts rising about three to four years before the seismic event. If it is seen that the temperature is rising for two or more years then a preliminary warning may be sounded.
It is also observed that about three to four months before an earthquake, the daily minimum and maximum temperatures rise. Initially, it may be one degree above normal. Gradually this will rise by about 3 to 4 degrees above normal. If such an increase is observed, then we should watch the situation more closely.
On the day of the earthquake the temperature could be as high as 6 to 10 degrees above normal. Such a thermo-meteorological situation was observed in Muzaffarabad too, where on Oct 8, 2005, the temperature was 10 degrees above normal.
The EMG may also collect some data from the nearest telephone exchange. They should collect details about the number of telephones installed and the number of complaints per month. For seismically quiet periods, both these figures will be more or less stationary, with a variation of plus or minus 10 per cent.
If it is observed that the number of complaints is gradually and steadily rising for a few months, then some changes may be taking place in the geomagnetic field. Generally for earthquakes of magnitude 7.0 or more, the change starts about eight months in advance and for earthquakes of magnitude 6.0 to 7.0, it starts about four to six months in advance.
These data are neither secret nor confidential and they can be used for monitoring the changes in geomagnetic field. As mentioned in one of my earlier articles on the subject, cellphones start malfunctioning about 100 to 150 minutes before the occurrence of an earthquake.
The seismo-electromagnetic precursors and animal and human seismic precursors have already been discussed in an article published in Sci-tech World on Oct 22, 2005. If it is seen that all animals, birds, insects and reptiles are behaving abnormally, then a quake could hit the area within a few hours.
Doctors, nurses and hospital administrators may keep a watch on the number of patients per day. If it is observed that the number of delivery and abortion cases and the number of OPD patients is five to seven times the daily average, then an earthquake may be imminent.
Remember, all the precursors described above are observed prior to medium to large earthquakes (magnitude 6.0 or more). For smaller magnitudes, the effects may or may not be observed.
To conclude, the subject of earthquake prediction may be in its infancy and some people may scoff at the idea. But please keep in mind that no government officer will come up to you and tell you that an earthquake may strike soon.
During the post-seismic period, the government officials usually come to deliver death certificates or to distribute the compensation amount. The administration is almost dormant during the pre-seismic and co-seismic periods.
Our aim is to save lives and to reduce the mortality and morbidity rates in quakes. Let us resolve, therefore, that formation of EMGs at different levels and locations will help mitigate all future seismic disasters. We may one day experience an earthquake similar to the one that hit Quetta more than 60 years ago, but the death toll in it should either be negligible or zero.
The author is a research seismologist who is based in Pune, India. Email: arun_bapat@vsnl.com
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