The developing countries of the Asia-pacific situated in the hazardous belt of the world are subject to natural disasters like floods, droughts, cyclones, earthquakes, windstorms, tidal waves and landslides and the vulnerability to these ha increased due to rapid urbanization, environmental degradation and a lack of proper planning and preparedness.
The undersea earthquake that occurred in the Indian Ocean on December 26, 2004 produced tsunamis and devastated the shores of Indonesia, Srilanka, India, Thailand and other countries with waves upto 15 meters in height. Even it hitted as far as 4500 km or more of its epicenter at the coast of East Africa especially Somalia. In fact it was among the deadliest natural disasters in modern history. This rare mega thrust earthquake took place in the Indian ocean off the western coast of northern Sumatra at a magnitude of 8.9 in the Richter scale. The hypocenter was at 3.316˚ N, 95.855˚ E, some 160 km west of Sumatra, at a depth of 30 km below mean sea level. This is at the extreme western end of the ‘Ring of Fire’, an earthquake belt that accounts for 81 percent of the worlds largest earthquakes. The quake itself was felt as far away as India, Malaysia, Myanmar, Thailand, Singapore, Bangladesh and Maldives. An unusually large quake in geographical extent an estimated 1200 km faulting stipend 20 20m long the seduction zone where the India plate dives under the Burma plate. The sea bed of the Burma plate is estimated to have risen several meters vertically up over the India plate, creating shock waves in the Indian Ocean. It is estimated that these shock waves traveled at a speed of 800 km/hr creating tsunamis which were less than a meter high in deep water, but resulted in huge waves when they reached the Indian coast and sowed destruction.
It was the largest since the 9.2 magnitude Good Friday earthquake off Alaska in 1964 and tied for fourth largest since 1900, when accurate global seismographic record keeping began. The energy released by an earthquake of the magnitude 9.0 in the Richter scale is equivalent to 32,000 megatons of TNT, which is more than 30 percent of the total energy consumed in the United States of America in 1 year.
The term ‘tsunami’ comes from the Japanese language Tsu meaning harbor and nami is waves. It was created by fishermen who returned to the parts to find them devastated though they were not aware of any violent waves in the open sea. A tsunami, though technically not, is commonly referred as a tidal wave. It is a series of waves called a wave train generated in a body of water by a pulsating or abrupt disturbance that vertically displaces a water column. It can be generated any disturbance that displaces a large mass of water such as an earthquake, landslide, volcanic eruptions, explosions, or meteor impact. They can inundate coastlines causing devastating damage to property and life. They can be generated when the sea floor abruptly deforms and vertically displaces the overlying water. Large vertical movements of the earth’s crust can occur at plate boundaries. When the dense oceanic plates ship under continental plates in process known as subduction, the resultant quakes generate tsunamis.
That act very differently from typical surf swells. They propagate at high speeds can travel trans oceanic distances with little energy loss and can cause damage thousands of miles from its origin. As a result there may be a gap of several hours between is creation and its impact on the coast. In open water tsunamis have extremely long periods from minutes to hours and long wavelengths of upto several hundred kilometers. They normal period between two waves, when the sea is in a rhythmic mood is only 10 seconds and a wavelength of 150m. The actual height of a tsunami wave is open water is often less than one meter, practically unnoticeable to people in ships and even to satellite eye, but they travel across the ocean at speeds from 500 to 1000 km/hr. As the waves slow down and begin to pile up. The waves become steeper and taller. A wave can reach to a height of 30 meters or more as it approaches the coastline. A wave becomes a shallow water wave when the ratio between the wave depth and its wavelength gets very small. As tsunami waves have an extremely large wavelength, they act as shallow waters waves in the deep areas of the ocean. Shallow water waves move at a speed that is equal to the square root of the product of the acceleration of gravity and water depth. For example, in the pacific ocean. Where the typical water depth is about 400m. a tsunami travels at about 200m/s with little energy loss, but a water depth of 40 meters the speeds of waves would be 20 m/s which is much slower the speed in deep ocean. Usually, undersea earthquakes give rise to waves between three and five distinct elephantine waves out of which the second or third is the largest. Usually, the coats in the shadow of affected land masses are fairly safe, as the tsunami propagate outward from their source and the waves may be stronger in one direction than another.
In the name of progress and industrialization we rape the nature left and right and invite natural calamities more and more so let us take care of her in every step and take care of our life.
Submitted to RB by Manish Patil