The epicentre lies where the circles intersect. Magnitude and intensity are the two ways in which a quakes strength is generally expressed. The magnitude is a measure that depends on the seismic energy radiated by the quake as recorded on seismographs. The intensity, in turn, is a measure that depends on the damage caused by the quake. It does not have a mathematical basis but is based on observed effects. A quakes magnitude is usually measured in terms of the richter scale.
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The slowest earthquake waves are the long, or l, waves which cause the most extensive damage as they move along the earths surface. Incidentally, l waves on sea floor cause sea waves on the surface called tsunamis. They rise to 100 feet or more and cause damage when they break on habitated coasts. All three kinds can be detected and recorded by sensitive instruments called seismographs. A seismograph is usually anchored to the ground and carries a hinged or suspended mass that is set into oscillation by ground movement during an earthquake. The instrument can record both horizontal and vertical ground movement in the form of wavy lines on paper or film. From the record, called a seismogram, it is possible to find out how strong the quake was, where it began and how long it lasted. The location of the epicentre of a quake is determined from the time of arrival of the p and S waves at the seismographic station. Since p waves travel at a speed of about 8 km per second and S waves at 5 km per second, it is possible to compute the distance of their origin from the seismic record. If the distance from three stations are computed, the exact location can be pin pointed. A circle of appropriate radius is drawn around each station.
Different institutions including the Indian Meteorogical Department and the Indian School of Mines, have after a study of mechanics of several earthquakes in the north- eastern region found that the thrust faulting was generally indicated along with Dawki fault and the Indo-burma border. Teiedemann, a member of the earthquake engineering Research Institute of the seismological Society of America, said in 1985 that the increased interplay activity near the north-eastern boundary in the Indian plate coupled with thrusting of the himalayan Burmese sector pointed to the danger of earthquakes. Tracking an earthquake: There are three kinds of seismic waves. Waves that move the fastest are called primary, or p, waves. These waves, like sound waves, travel longitudinally by alternate compression and expansion of the medium, like the movement of the bellows of an accordion. Somewhat slower database are the secondary, or s, waves which propagate transversely in the form of snakelike wriggles at right angle to the directions of travel. These cannot travel through liquids or gases.
One of the the reasons for this region being prone to earthquake is the presence of the young-fold Himalayan mountains here which have frequent tectonic movements. Zone iv which is the next most active region of seismic activity covers sikkim, delhi, remaining parts of Jammu and Kashmir, himachal Pradesh, bihar, northern parts of Uttar Pradesh and West Bengal, parts of Gujarat and small portions of Maharashtra near the west coast. Zone iii comprises Kerala, goa, lakshadweep, remaining parts of Uttar Pradesh and West Bengal, parts of Punjab, rajasthan, maharashtra, madhya pradesh, Orissa, andhra Pradesh and Karnataka. The remaining states with lesser known activity fall in zone. The states of Jammu and Kashmir, punjab, himachal Pradesh, Uttar Pradesh and Bihar, the bihar-Nepal border, the rann of Katchh in Gujarat and the Andaman Islands fall into the unstable belt which stretches plan right across the globe. The high seismicity of the Indian subcontinent arises from the tectonic disturbances associated with the northward movement of the Indian plate, which is underthrasting the eurasian plate. The himalayan region has been the site for great earthquakes of the world of magnitude greater than.0. This highly seismic belt is a branch of one of the three major seismic belts of the world called the Alpide-himalayan Belt. The high seismicity region extends from Hindukush in the west to sadiya in the northeast which further extends down to the Andaman and Nicobar Islands.
Based on seismic data and different geological and geophysical parameters, the bureau of Indian Standards (BIS) had initially divided the country into five seismic zones. In 2003, however, bis redefined the seismic map of India by merging zones i and. Thus India has four such zones now—ii, iii, iv and. There is thus no part of the country that can be termed earthquake free. Of the five seismic zones, zone v is the most active region and zone i shows least seismic activity. The entire north-eastern region falls in zone. Besides the north- east, zone v includes parts of Jammu and Kashmir, himachal Pradesh, Uttarakhand, rann of Kachch in Gujarat, northern Bihar and the Andaman and Nicobar islands.
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Earthquake zones: The movement of unique the plates and occurrence of earthquakes seem to be concentrated in certain areas or bold zones of the earth. Based on intensity and frequency of occurrence, world map is divided into the following earthquake zones or belts—. Circum-Pacific Belt Surrounds the pacific Ocean and accounts for more than three-fourths of the worlds earthquakes. Sometimes called the ring of Fire, its epicentre are the coastal margins of North and south America and East Asia. These represent the eastern and western margins of the pacific Ocean respectively.
The occurrence of maximum number of earthquakes in this region is due to four ideal conditions— (i) Junction of continental and oceanic margins (ii) Zone of young folded mountains (iii) Zone of active volcanoes (iv) Subduction zone of destructive or convergent plate boundaries. Mid-Continental Belt: Also called the mediterranean Belt or Alpine-himalayan Belt, it accounts for about 21 per cent of the total seismic shocks. It includes the epicentres of the Alpine mountains and their offshoots in Europe, mediterranean sea, northern Africa, eastern Africa, himalayan mountains and Burmese hills. Mid-Atlantic Ridge belt: The epicentres of this region are along the mid-Atlantic Ridge and the islands near the ridge. This belt represents the zone of moderate and shallow focus earthquakes—the reason for this being the creation of transform faults and fractures because of splitting of plates followed by their movement in the opposite direction.
Where two places converge or collide, a deep trench forms and one plate is deflected downwards into the asthenosphere which lies below the crust and the lithosphere. When two thick continential plates collide, rocks on the land are relatively light and too buoyant to descend into the asthenosphere. The result is a huge zone of crushing, with rocks and other materials being folded. And this is how the himalayas have emerged or, in fact, are continuing to emerge. As the deformation of the plate margins goes on, energy builds up in rocks in the form of elastic strain which continues till it exceeds their elastic limits and the rocks give way.
The sudden release of stored elastic energy causes earthquakes. Earthquakes in India are caused by the release of elastic strain energy created and replenished by the stresses from the collision between the Indian plate and the eurasian plate. The most intense earthquakes occur on the boundaries of the Indian plate to the east, north and west. In the Indian plate, faults are created when this rubs against the eurasian plate. (When an earthquake occurs along a fault line within the plate, it is called an intra-plate earthquake. The majority of the earthquakes occur along plate boundaries.). Earthquakes are also caused by volcanic activity. Construction of large water reservoirs may also cause earthquakes—these are called reservoir-induced earthquakes.
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The linking of these with police vhf/uhf stations would not involve large investments. This would be a cost effective and write reliable communication system for disaster warning and mitigation. Earthquake : Stated simply, an earthquake is a vehement shake of the earth from natural causes. Technically an earthquake is a phenomenon of strong vibrations occurring on writing the ground, consequent to release of large amount of energy within a short period of time because of some disturbance in the earths crust or in the upper part of the mantle. Causes: advertisements: The theory of plate tectonics offers a comprehensive explanation for several geological phenomena — continental drift, mountain building and volcanism, and, of course, earthquake. According to this theory, when the molten mass that was the earth billions of years ago cooled down, the crust that was formed was not one homogenous piece but broken into about a dozen large plates and several smaller ones with their thickness ranging from. The plates are in incessant motion, with speeds of about 1 cm to 5 cm a year. This mobile jigsaw puzzle is what is termed as the continental drift, which results in the formation of mountains, midoceanic ridges, ocean trenches, volcanoes and seismic energy buildup.
This assumes that the earth stations at the two ends are suitably located to remain unaffected. Further link between the earth station and the affected area is usually through microwave/ land line, which has its limitation as it may break down. The most effective way of dissemination of warning is Disaster Warning System (DWS) used by the imd for issue of cyclone bulletin to the coastal areas. This could be extended to the entire earthquake/ flood prone areas. Experience has shown that it remains completely unaffected under the severest cyclonic condition. However, the system is limited to one way communication only. For effective two way communication, vhf/uhf links should be established from every earth station to the affected zone. Use of existing police vhf/uhf link can be made. The only addition required is the missing link between the nearest earth station to police headquarters.
warming have already started showing their precursors, giving sufficient time to control and avoid these hazards by long term planning. On the contrary, in earthquakes no proven methods has yet been evolved to give any prior warning and so post-hazard mitigation is the only alternative. Role of Communication For a developing country like india, the role of communication in disaster mitigation is extremely critical. Vast areas of the country do not have telephone/ telegraph links. These can neither be provided in a short span of time available for mitigation nor are there resources to. We have to depend on existing links, many of which completely break down during the disaster. The various types available for dissemination of disaster warning as well as arranging mitigation are: (a) land line links; (b) underground cable links; (c) wireless links; (d) microwave (los and (e) satellite links. The only effective communication which is likely to remain completely or partially unaffected is the satellite link.
Management: The management aspect of disaster may be classified as: (a) early warning system; (b) rescue operations; (c) relief operations; (d) rehabilitation; and (e) long range planning. The most important is the early warning systems. Unless sufficient advance thesis notice is available, evacuation of the population likely to be affected cannot be undertaken. Advertisements: There are two aspects of early warning system. One is the availability of an effective technique to forecast the disaster with its extent and the other is effective communication of the same to the civil authority responsible for rescue operations. In some phenomena, such as cyclones, flood, etc. The time available to respond to the hazard is of the order of a few days. Hence early warning, communication, and rescue operations are possible.
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Advertisements: Here is your comprehensive essay on Natural Disasters! Nature and Management : A natural disaster is unforeseen, severe and immediate. Pollution, ozone depletion in the stratosphere and global warming come in this category. Natural disasters include cyclones, earthquakes, floods, drought (though these two are now being increasingly considered man- made disasters) heat and cold waves, landslides, avalanches, flash floods, severe thunderstorms, hail, low level wind shears, and microburst. Image courtesy : g, advertisements: The destructive potential of any natural hazard is estimated basically by its spatial extent and severity. Spatial extent upto which the effect of a disastrous event could be felt may easily be classified into small, medium and large scales. The phenomenon extending from a few kilometers barbing to a few tens of kilometers are termed as small scale. Growing industrialisation and unjustified exploitation of natural resources have brought our echo system to a verge of non-reversibility and imbalance. This has led to a threat from a set of natural hazards like pollution, global warming and ozone depletion on large or global scale.