A series of earthquakes, measuring between 5.0 and 6.3 on the Richter scale, jolted the region from the Andaman and Nicobar Islands to Sumatra since late Friday night, raising the number of aftershocks in the area after Sunday's massive quake to over 80.
While two earthquakes of moderate intensity occurred near Car Nicobar, two more had their epicentre near the Great Nicobar Island, the Indian Meteorological Department (IMD) said in Delhi.
The strongest measuring 6.3 on the Richter scale, was recorded at 1156 IST to the West of Great Nicobar on Saturday. It had followed a 5.5 intensity trembler epicentred south of Great Nicobar.
The quakes had their epicentre at 5.6 degrees North Latitude and 9.7 degrees East Longitude and 6.0 degrees North and 93.2 degrees East, respectively.
Aftershocks measuring 5.2 and 5.0 on the Richter scale earlier shook the Car Nicobar region at 2332 IST on Friday night and at 0340 IST early Saturday, respectively, the Met Department said.
While the epicentre of the first quake was at 8.1 degrees North Latitude and 92.0 degrees East Longitude, the other was epicentred at 9.28 degrees North and 92.87 degrees East.
Meanwhile, at 0726 IST Saturday, a 5.2 intensity quake occurred off the west coast of Sumatra. It was epicentred at 4.3 degrees North Latitude and 94.6 degrees East Longitude.
So far, these aftershocks have not resulted in casualties or damage to property.
Meanwhile, scientists in the United States have cautioned the Indian government that aftershocks of the December 26 quake off Sumatra are moving northwards and can potentially trigger a major earthquake in Assam.
The scientists at the Center for Earth Observing and Space Research in George Mason University in Virginia, who have been analysing the seismic data since December 26, have found that the aftershocks are moving northwards.
"If the sequence of these aftershocks moves further north then it may trigger a very big earthquake in the Assam region," Ramesh P Singh, a member of the team and vice-chairman of the International Union of Geodesy and Geophysics (IUGG) Risk Commission said.
Singh said the magnitude-5 earthquake on December 30 near Myanmar reported by the US Geological Survey was probably caused by the aftershocks. Its epicenter falls on the trajectory of the aftershocks.
"No big earthquake has occurred in the Assam region for a long time and scientists believe that it is due any time," Singh, who is on leave from Indian Institute of Technology (Kanpur), told PTI.
Singh has requested government agencies to keep a close eye on the aftershocks.
In Assam, India's Department of Science and Technology has established a GPS satellite network for monitoring crustal movements.
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