A strong earthquake measuring 7.0 on the Richter struck off the northeast tip of Sulawesi island Indonesia. Indonesia -a country of over 230 million people-suffers frequent earthquakes due to its location on the Pacific Ring of Fire. The Ring of Fire has 452 volcanoes and is home to over 75% of the world’s active and dormant volcanoes. The epicenter was located about 320 kilometers north-northeast of the town of Manado, the US Geological Survey said.
Northeastern Indonesia is characterized by complex tectonics in which motions of numerous small plates are accommodating large-scale convergence between the Philippine Sea and Sunda plates. In the region of today's earthquake, the Philippine Sea plate moves west-northwest with respect to the Sunda plate at a velocity of about 62 mm/year. Locally, arc-arc collision is occurring between the Sangihe and Halmahera micro plates, wedging between them the Molucca Sea micro plate, which subducts beneath both (i.e. to the east and west) and forms an inverted-U-shaped seismic zone. Seismicity within the Molucca Sea plate is active to depths of approximately 260 km to the east and 400 km to the west. The tectonic setting of this region is unique in that it is the only global example of an active arc-arc collision consuming an oceanic basin via subduction in two directions.
The earthquake occurred approximately 30 km off the western coast of the Pulau Salebabu (Indonesia) in an area that has seen large earthquakes in the past. Since 1986, there have been two earthquakes with magnitude greater than 7 in this region.(USGS)
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The Islands of Indonesia are continuously rising.-g.ponmudi,scientist.chennai.
Soon after Tsunami, which killed more than two and a half lakhs of people and had originated from the island, Sumatra, it was found out that, after the earthquake the north western part of the island simeulue, which was in that region had risen about three feet high above sea level. On account of this, a new shore had formed on the north western part of the island. In addition to that; the sea sponges which were on the sea bed were visible above the sea level!
Three months after the earthquake on 26th December, 2004, another quake occurred on 28th March 2005 after which simeulue was found to be four feet above sea level. Apart from this, for an area of about three hundred kilometers, sea sponges which are normally found below the sea could be seen from all visible areas!
Why did the island rise four feet above sea level ?
As the molten rock keeps cooling gradually, the rocky plates that are formed at different levels are of less thickness and density and they keep rising continuously.
The main reason is that, when the molten rock cools, the water and hot gases get released and the rocky plates that are formed are of lesser thickness than the magma in which they formed. Water has a higher density and the ice cubes formed from it have a lower density and they tend to float on water Likewise, the molten rock material which has a higher density produces rocky plates which have a lower density and these move above sea level and form islands.
When new plates are produced by the molten rock material, they start moving upwards thereby pushing the plates which were already formed. The plates suddenly start rising upwards due to intense pressure.
Similar to the ripples that are formed and expanded when a plate of water is hit at the centre from below with a finger, when the island simeulue, which was found in the central part of the Indian Ocean suddenly rose up, the water was pushed aside in all directions and only this resulted in Tsunami.
The frequent occurrences of earthquakes and Tsunami in Indonesia are only due to the sudden rising of the islands.
But, the geologists have come up with a different explanation for the earthquakes which occur there. They say that, about six and a half crores of years ago, India was an island on the southern part of the equator. It moved slowly towards north and collided with Asia about five crores of years ago and it is still continuing its movement. The geologists also opine that due to this movement, when the indo-Australian plate suddenly went below the Burmese plate on December 26th, 2004, an earthquake occurred. There is no truth in what they say because even six and a half crores of years ago India had been part of Asia in the same place as it is found now.
The fossils of mammals which lived in Asia six and a half years ago have been excavated in the form of bones by Professor Ashok Sahani of Punjab University and Professor G.V.R. Prasad of Jammu University in the village of Naskal at Andhra Pradesh and they prove that the above statement is true. So, as per the researchers’ opinion, India had not been an island on the southern part of the equator about six and a half crores of years ago
So, it is proved that even six and a half crores of years ago India had been part of Asia in the same place as it is found now and is not moving in the north eastern direction. Therefore the indo-Australian plate did not go suddenly below the Burmese plate.
So the earth quakes on 26 -12 -2004 and 28 – 3 -2005 and the Tsunami are only the result of the rising of the island, simeulue, above its original level.
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