Dr Mansoor Ahmad Qazi
What are Earthquakes
* The shaking or trembling caused by the sudden release of energy
* Usually associated with faulting or breaking of rocks
* Continuing adjustment of position results in aftershocks Earthquakes and volcanoes occur due to internal forces of the earth. The central part of the earth is very hot. Due to this the minerals remain in a molten (plastic state) called magma. When water penetrates through the cracks of fissures of the earth they turn to vapour because of the internal heat. This vapour exerts tremendous pressure upward and tries to release the pressure formed. This release of pressure causes a lot of energy to be released and a series of waves are started which travel away from the break through the earth to cause earthquakes. The earthquake is a vibration of the earth caused by the waves that travel through it. Major Earthquakes are always followed by the tremors of less magnitude.
Earthquakes occur along plate margins (where plates meet). When plates move past, towards or away from each other the movement is not smooth. Friction causes the plates to get stuck. This causes pressure to build up. Earthquakes occur when this build up of pressure is released. The point where the Earthquake starts is called the focus. Energy waves race rapidly from this point. The point at ground level, directly above the focus is called the epicenter. Earthquake is a violent tremor in the earth’s crust, sending out a series of shock waves in all directions from its place of origin or epicenter.
For instance, if you throw stone in a pond of still water, series of concentric waves are produced on the surface of water, these waves spread out in all directions from the point where the stone strikes the water similarly, any sudden disturbances in the earth’s crust may produce vibrations in the crust which travel in all directions from point of disturbances.
Keep in mind that aftershocks — smaller tremors — can occur for months after the initial earthquake, though the strongest ones will likely occur in the first few hours or days. Aftershocks can cause additional damage or lead unstable structures to collapse. Unsecured items could fall off shelves, which is also a concern when opening cabinets or closets. If you feel like the structure you’re in may not be structurally sound, leave and find a safe space to stay until an expert can confirm the building’s integrity.
Intensity Scale
The earthquake that recently lit Chenab Valley was of magnitude 5.8 and was comparatively small; hence damages caused by this event clearly indicate that the region is highly vulnerable to a major disaster in the future. Series of tremors struck erstwhile Doda, Bhaderwah, Chirala, Bhalesa and Kishtwar. Tremors triggered panic in the entire affected areas, where people are still sleeping outside their homes in tents or open areas.
In the absence of proper design and construction methods, and lack of quality control, masonry buildings and RC frame buildings have performed rather poorly. This indicates very high level of seismic vulnerability of the region. Discontinuous RC columns were commonly observed in several RC frame buildings in J & K, therefore RC frame lateral load resisting system could not be developed in such buildings. Such design and construction practices may have severe consequences as seen in Ahmedabad during Bhuj earthquake of 26 January, 2001.
Good construction practices need to be propagated, and the seismic codes need to be enforced (IS:1893 2002; IS:13920 1993; IS:4326 1993). People (including engineers) need to be sensitized about basic construction issues, and seismic hazard associated with the region of J & K. Systematic changes are required in building industry for better training of engineers, and involvement of different stake holders (architects, engineers, material suppliers, contractors, material manufacturers, public, etc) in actual construction process of structures. Another urgent requirement is training and supply of simple literature to government as well as private engineers and to local people on how to incorporate simple techniques in buildings to make them earthquake resistant. Existing deficient buildings, particularly the important heritage structures,should also be repaired/strengthened on priority. Resource materials on repairing and strengthening of existing RC and masonry structures, such as, IS:13935 1993, can be quite useful in this.
Government departments, NGOs, industries, and material suppliers can collectively bring about a change for the seismic safety in the area.
Reinforced concrete buildings on steep slope collapse due to the following:
* Improper construction site on a foothill.
* Poor detailing of the reinforcement (lack of concrete confinement in the columns and at the beam-column joints, inadequate splice length).
* Seismically weak soft story at the first floor.
* Long cantilevers with heavy dead load.
Earthquake Prediction:
Yet at the moment, earthquake prediction remains a matter of myth, of fabulations in which birds, snakes, fish and rabbits somehow sniff out the coming calamity.
Some changes which are noticed before an earthquake occurs are as under:
* Elephants scream and run for higher ground.
* Dogs refuse to go outdoors.
o Flamingos abandon their low-lying breeding areas.
* Zoo animals rush into their shelters and could not be enticed to come back out.
The belief that wild and domestic animals possess a sixth sense-and know in advance when the earth is going to shake-has been around for centuries.
Wildlife experts believe animals’ more acute hearing and other senses might enable them to hear or feel the Earth’s vibration, tipping them off to approaching disaster long before humans realize what’s going on.
– Unusual animal behavior
– Changes in water level
– Temperature change
– Large scale fluctuations of oil flow from oil wells
– Foreshocks or minor shocks before major earthquake
– Changes in seismic wave velocity.
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