National Tsunami Warning Centre kept close watch on earthquake
Y. Mallikarjun HYDERABAD: Although Tuesday morning's earthquake North of Andaman was undersea, it did not generate a tsunami because the mechanism that triggered it was different from the one that normally precedes a tsunami, said a seismologist here on Tuesday.
According to R.K.Chadda, senior scientist and seismologist at the National Geophysical Research Institute (NGRI), the large earthquake (7.6 on the Richter scale) occurred within the Indian plate and its mechanism was dominated by a combination of 'strike-slip and normal faulting'. In contrast, the massive Sumatra earthquake in December 2004 occurred in the subduction zone and experienced a 'thrust-faulting' mechanism - usually responsible for a tsunami-generating quake.
He said the magnitude was also less than that of the 2004 tremor because it occurred within the plate. It was categorised as a large tremor which could be normally felt up to 1,000 to 1100 km. Tuesday's earthquake was felt by the people along the East Coast up to Orissa. He said four after-shocks of magnitudes ranging from 5.2 to 4.8 were recorded subsequently, a normal pattern whenever a large earthquake occurrs. However, the intensity of the after-shocks would gradually taper off, he said, ruling out the possibility of another big earthquake of the magnitude of 9 on Richter scale in the immediate future in the same region.
Meanwhile, the Hyderabad-based National Tsunami Warning Centre kept close watch on the situation and issued the first bulletin within six minutes of the earthquake stating that it was evaluating its tsunamigenic potential. Subsequently, it issued a second bulletin at 2.45 am pointing out that there were no significant water level changes in the Bottom Pressure Recorders (BPRs) and tide gauges in the Andaman, after receiving realtime data from them.
Satish Shenoy, Director of the Indian National Centre for Ocean Information Services (INCOIS) - which houses the Tsunami Warning Centre - said that no tsunami alert was issued as it was unnecessary. He said the Pacific Tusnami Warning Centre issued a tsunami watch and withdrew it later. The information was shared with other countries along the Indian Ocean rim and also with regional tsunami warning centres in Australia, Indonesia, Thailand, Maldives and Sri Lanka.