EARTH QUAKES, TSUNAMIS AND CONTINENTAL DRIFT 

N.Nandhivarman

Tsunami hit Tamilnadu in  recent years and people were taken aback at its ferocity. The least expected unfolding of the Nature’s fury has stirred a debate on the changes in our coastline. Why did it happen and how it happened are subjects of current debate. Earth’s surface rests divided into 12 plates. Now the 13 th plate is in the offing. Throughout history scientists believe continents to be drifting, moving closer, or breaking from one another. Pangaea, the most recent super-continent on Earth began to break 160 million years ago. Paul Hoffman, Professor of Geology at Harvard University opines that while Pangaea broke up the Atlantic Ocean opened splitting North America from Eurasia. Then North America parted from Eurasia subsequently South America from Africa, Australia, Antarctica and India separated from Africa creating the Indian Ocean. The same scholar says, “ Atlantic and Indian Oceans continue to widen while Pacific gets smaller. In 100 million years North America and Asia will probably drift into each other”. Paul Hoffman had already named the new super-continent as Amasia.

Jeffrey Welssel at Columbia University’s Lamont-Doherty Earth Observatory says, “ The result of this crucial stage in the collision between India and Asia is the breakup of the Indo Australian Plate into separate Indian and Australian plates”. He also said “ In The Central Indian Ocean Nature is conducting a large scale experiment for us, showing us what happens to oceanic lithosphere (earth’s outer layer) when a force is applied.” This experiment had its repercussions, when on fault lines earthquakes hit almost exactly where Indo Australian plates have broken.

Group of researchers from NASA’s Goddard Space Flight Center have provided with schematic global tectonic activity map, which shows several types of faults, active spreading centers, and volcanoes. The fault-lines or geo fractures are areas where we must watch and take all precautions in constructions to save lives.

This may be a global watch, but Pondicherrian’s have specific areas to observe. A Report on Ground Water Survey and Exploration in the Union Territory of Pondicherry and its environs by a team of experts from Central Ground Water Board, Southern region in March 1973 says that “ The photo-geological study has also confirmed the existence of the fault to the west of the coastline a straight scarp running almost parallel to Pondicherry- Markanam Road” That finding was made three decades ago.

Dr.S.M.Ramasamy Director of Center for Remote Sensing of Bharathidasan University as early as 1993 said, “ The East North East- West South West trending faults on the contrary are showing left handed (sinistrel) ongoing translational movements. Such sinisterly and dextrally moving faults display definite morph tectonic anomalies in the remotely sensed data and also in the field. In addition, there is a conspicuous land subsidence between Pondicherry in the North East and Cumbum valley in the South West.

One such graben has been established along north east- southwest trending faults in between Pondicherry-Cuddalore in the northeast and Cumbum valley in the Southwest. It is significant to observe that the earthquake epicenters fall along such NE-SW trending fault in Cuddalore, Ariyalor, Dindigul and Kodaikanal.

In view of a geo-fracture i.e. fault line from Kalapet in Pondicherry to Cumbum Valley in South Tamil Nadu, great caution must be taken in construction of high rise structures wherever fault lines have been identified. Earthquake resistant construction design in places where one fault line passes, as mentioned above, is need of the hour. There are pictures taken by satellites using remote sensing techniques had identified studies covering Tamil Nadu its and various fault lines. It is high time sky scrappers do not come up in the fault line and quake prone areas.

While Earthquake precautions are need of the hour, the new threat to Tamil Nadu’s coast comes by way of Tsunamis. Tsunami is a known phenomenon in Pacific Ocean stretching from Chile in Latin America to Japan in Far East Asia. Seismic disturbances, coastal earthquakes, volcanic eruptions or under sea landslides that jolt the ocean floor cause tsunamis, which travels at speeds up to 500 miles per hour and reaches heights between 50 and 100 feet. Tsunami observatories and Earth Quake observatories must be set up for early warning systems. People living in low-lying coastal areas have faced the brunt. “ It is high time fishermen settlements are shifted to higher grounds. World Bank and global assistance that is forthcoming must be utilized to create fishermen colonies in high ground ’’opines Narambai Kanagasabai, President of Narambai Fishermen Panchayat of Pondicherry state.

The green house effect causes rise in sea water levels. Scientists have predicted that by 2100 A.D the rise in sea level will be between 0.5 to 1.5 meters. Before 1.5 million years Sea was closer to Madurai and before 90,000 years Chennai, Pondicherry and Vedaranyam were surrounded by sea. Due to fall in sea levels 65,000 years ago India and Ceylon joined and when sea level rose around 27,000 years ago they parted. Then 17,000 years ago due to fall in water level both joined and when water rose they parted. This is the study-report of Bharathidasan University’s Earth Sciences Department. All these studies and past history makes it clear that our coastline had undergone changes over centuries. Poompuhar of Chola Empire is beneath the seas. Sirkazhi once a coastal town is now an interior town. So changes in our coast is continuous. Caution must be taken about all dwellings in our coast, and let this tsunami attack be an eye opener.

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