Major earthquake keeps tsunami scientists on tenterhooks

By Syed Akbar
Hyderabad, April 11:  A major earthquake measuring 8.5 on the Richter scale off the west 
coast of northern Sumatra in Indonesia on Wednesday afternoon triggered tremors in 
several parts of South India sending people into panic.

The city-based Tsunami Early Warning Centre (TEWC), which issued a tsunami alert for 
coastal areas in Tamil Nadu, Kerala, Karnataka and Andhra Pradesh besides Andaman and 
Nicobar islands, later withdrew it as the seismic waves could not trigger a large 
tsunamigenic event in the Indian Ocean. Wednesday’s earthquake is the seventh biggest 
earthquake in the last 100 years and it triggered a series of aftershocks. The TEWC 
recorded as many as seven earthquakes of magnitudes less than 7 after the major one 
measuring 8.5.

The tsunami threat receded as the earthquake generated seismic waves horizontally and 
this explains why tremors were felt thousands of kilometres away from the epicentre in 
Sumatra. Had the waves traveled vertically there would have been a possibility of a major 
tsunami generating in the Indian Ocean.

Thousands of people came out of homes, offices, schools and shopping complexes as mild 
tremors were felt in Vijayawada, Nellore, Ongole, Visakhapatnam, Srikakulam, Kakinada and 
Machilipatnam. Reports of tremors also came in from Chennai and other parts of Tamil 
Nadu, Kolkata, Bengaluru, Bhubaneswar and Thiruvanantapuram, and parts of Assam. Andhra 
Pradesh and Tamil Nadu bore the brunt of the tsunami on December 26, 2004.

“The tremors were due to the earthquake in Sumatra and there was no threat of an 
earthquake in Andhra Pradesh. It was a major earthquake and thus the tremors were felt in 
far away places,” said Dr RK Chada, senior scientist at the city-based National 
Geophysical Research Institute.

Keeping in view the huge loss to human life and property in the December 26, 2004 tsunami 
in Andhra Pradesh, Tamil Nadu and Andamans and Nicobar islands, the National Disaster 
Management Authority (NMDA) alerted State governments, the Coast Guard and the Army. 
Tsunami sirens were sounded in coastal villages and district authorities swung into 
action warning people living on the shore.

The tremors in Andhra Pradesh and Tamil Nadu came handy for anti-nuclear power plant 
activists, who questioned the safety of the existing plants in Tamil Nadu and the 
proposed mega nuclear park at Kovvada in Srikakulam district. Meanwhile, officials at the 
Kudankulam Nuclear Power Plant, which is all set to go critical in the next few months, 
said work at the site was not affected.

"We received the alert from Indian National Centre for Ocean Information Services 
(Incois) and we are generally on alert. But our work is continuing," said M Kasinath 
Balaji, Kudankulam plant site director. The Nuclear Power Corporation of India Limited, 
which has revisited its units after the Fukushima event in Japan last year, built 7.5 
metres high walls around the Kudankulam plant. The nuclear plant was constructed at a 
raised platform to avoid inundation in case of a major tsunami.
According to reports from Indonesia, the first 8.5 magnitude earthquake near Sumatra had 
spawned a wave around 30 inches high but caused no serious damage. The second, an 8.2 
magnitude aftershock also struck off the coast of Indonesia's Sumatra island. Operations 
at Chennai port were suspended because of the tsunami alert.

The projections issued by the Indian Tsunami Early Warning Centre (ITEWC) showed the 
tidal waves triggered by the quake hitting parts of Nicobar, Komatra and Katchal minutes 
after it struck the region at 14:08 IST.  The ITEWC also issued an alert for coastal 
Tamil Nadu, Andhra Pradesh and the Andaman islands forecasting the arrival time of the 
first wave.

The Andhra Pradesh government put officials of nine coastal districts on high alert. 
Instructions were given to them to take all precautionary measures and utilise the 
services of armed forces, if required, to meet any eventuality. Collectors were asked to 
open control rooms and ask fishermen, who ventured into the sea, to return home 
immediately and also evacuate people from the beaches.

NDMA vice-president M Sashidar Reddy said no waves were noticed in Andaman and Nicobar 
Islands and the possibility of a tsunami was virtually ruled out.