WASHINGTON, Jan 1: A US-based agency reported on Saturday that aftershocks of last week's quake off Sumatra are moving northwards Assam and may cause a big quake there.

Scientists at the Centre for Earth Observing and Space Research in George Mason University, Virginia, said they had found aftershocks moving north along a 90-degree ridge. Scientists at this university near Washington have been analyzing the seismic data since Dec 26, when last week's earthquake and subsequent tsunamis played havoc in 11 countries along the Indian Ocean.

"If the sequence of these aftershocks moves further north then it may trigger a very big earthquake in Assam region," said Ramesh P. Singh, vice-chairman of the International Union of Geodesy and Geophysics.