Ratna Kurnia Sari, an Indonesian woman, being pulled out from the rubble of a collapsed building in Padang, Sumatra, on Friday. Rescue efforts are under way for three girls still buried under the debris of their school building in Padang. The girls were attending an English class on the ground-floor of the school when the quake brought the building down, sending their classroom deep below the ground, killing four students. A relief co-ordination team said they could hear faint voices of the girls from under the rubble. (AFP)
New Delhi, Oct. 2: The earthquake off western Sumatra on Wednesday that killed over 1,000 people is the latest that has left scientists baffled and wondering how many more instalments of tectonic strain will be released before this Southeast Asian region becomes seismically quiet.
The 7.6-magnitude undersea earthquake near Padang in Sumatra, Indonesia, follows at least eight high-magnitude temblors that have jolted Sumatra since the magnitude 9.0 quake that triggered the December 26, 2004, tsunami, which killed about 230,000 people in 11 countries.
Scientists in Hyderabad who simulated the effects of the earthquake on computer said it did not drive a tsunami to Indian shores, and confirmed their forecast through real-time observations of readings from instruments in the ocean.
The water level rose by 60cm near Padang about 45km from the epicentre, but there was no rise either at Campbell Bay or Port Blair, said oceanographer Srinivasa Rao at the Indian National Centre for Ocean Information Systems (INCOIS), Hyderabad.
Scientists say each high-magnitude earthquake near this region of Sumatra releases vast amounts of accumulated underground strain that has built up while the Indian oceanic plate moves beneath Myanmar and Indonesia.
The trouble is no one has any idea how much energy is still left to be released, said Shyam Sundar Rai, professor of geophysics at the Indian Institute of Science Education and Research, Calcutta.
After the 2004 quake, it was assumed that a large amount of strain had been released, but high-magnitude earthquakes have continued to occur off the coast of Sumatra.
Until 2004, there had been virtually no strain measurement experiments in the region, Rai told The Telegraph. Such measurements allow scientists to track the accumulation of strain and predict which areas are ripe for earthquakes.
Over the past five years, Rai said, Japanese, French and US scientists have deployed ground and seabed instruments in the region to monitor tectonic forces. These instruments are now helping scientists measure strain build-up in the region.
Were learning through instrumentation for the first time in history how the earth behaves after a major event of magnitude 9, Rai said.
Strain measurement studies cannot, however, predict when the next earthquake will occur. The strain doesnt ever go to zero, cautioned Srinivasa. When the accumulated strain breaks up at one place, it builds up elsewhere.
Scientists say similar strain measurements in the Himalayan region have revealed seismic gaps — stretches that have not experienced a high-magnitude earthquake for considerable time — which should be considered likely areas for an earthquake of a magnitude of about 7. One such seismic gap is the Garhwal region, Rai said.