Wednesday, March 16 2005 13:07 Hrs (IST) - World Time -

New Delhi: Some Islands of the Andaman and Nicobar archipelago have shifted southwest by "a few metres" after the December 26 earthquake near Sumatra in Indonesia, according to a study by Indian geologists.

Chatham, Havelock, Diglipur, Hut Bay, Car Nicobar, Campbell Bay and Barren Island have shifted after the magnitude 9.3 earthquakes, scientists at the Centre for Earth Science Studies (CESS) in Thiruvananthapuram said.

The finding was made from a geodetic survey using the American global positioning satellite (GOS) system, to CESS seismologist C P Rajendran said.

Signals from the constellation of 24 GPS satellites help to accurately determine coordinates of any point on the ground and establish the distance between any two points through triangulation. Continuous reception of the signals gives a clue to whether a point has moved or not.

Preliminary estimates from the GPS survey around Andaman and Nicobar suggest the Islands have shifted southwestward by "a few metres", the scientists said.

The GPS survey was sponsored by the Department of Science and Technology "to quantify the impact of this earthquake and the accompanied tsunami on the Andaman and Nicobar Islands", Rajendran said.

"The December 26 earthquake, generated at the shallow interface of the sub-ducting Indian lithosphere is of great interest for the seismology community due to its unprecedented rupture size," Rajendran's report, of the survey conducted in January-February, said.

Rajendran said that a GPS receiver loaned from the National Geophysical Research Institute (NGRI) in Hyderabad was taken to Port Blair and has been functioning since January 10. "Data from this receiver is expected to bring out the post seismic deformation happening now at Port Blair," he said.

The study by CESS scientists also showed that some parts of the Andaman and Nicobar Islands "subsided and some got uplifted". Wandoor area on the east coast of Port Blair has subsided allowing high tide water covers the road, he said.

In contrast, the west coast of North Sentinel Island, home of the Sentinelise tribe, was lifted up by a half metre and a similar uplift occurred on the west coast of Middle Andaman, the study added.