Close monitoring of faults neighbouring the one that ruptured under the Himalayas on Saturday in the 7.6 magnitude earthquake is required as the Indian plate boundary has become seismically very active, a top Indian seismologists said.

The wave of strong earthquakes since the Sumatran quake last December that triggered the Tsunami [Images] suggest that the Indian plate boundary has become seismically very active and needs watching, they warned.

• Terror from the Earth

The Indian plate is one of the 14 major plates that are locked on to the surface of the earth like a jigsaw.

Strain built up along the boundaries due to motion of the rigid plates, when released, manifest as earthquakes.

"The 9.3 magnitude Sumatara quake in December 2004, followed within three months by an 8.6 magnitude quake near the same place and now this one in Pakistan suggest the Indian plate boundary has become very highly active," says Janardhan Negi, a well known seismologist with Madhya Pradesh government.

"This high frequency of strong quakes is unusual," he told PTI.

"It is true that some of the plate boundaries including the Indian plate have become relatively very active," C P Rajendran of the Center for Earth Science Studies in Thiruvananthapuram said.

He, however, added that scientists do not know if this is a coincidence, an artifact of observation, a temporal burst of activity, or a part of regional deformation 'wave'.

The frequency of earthquakes (along the Indian plate boundary) has increased and we expect this trend to increase because of stress triggering. The neighbouring faults need to be closely monitored, Rajendran said.

The Kangra region, is one of those that need monitoring, as it had experienced a devastating quake in 1905.

Vineet Gahalaut of the National Geophysical Research Institute in Hyderabad said the 'Kangra rupture can fail again in a 7.5 quake or as part of a much larger earthquake'.

American geologists Roger Bilham and Kali Wallace of the University of Colorado had told a conference in India six months ago that 'the Kangra region, like other parts of the Himalayas, must now be considered vulnerable to a future large earthquake, despite having experienced one 100 years ago'.

They said that the entire Himalayan region from the eastern Indian plate boundary in Myanmar to the western plate boundary through Pakistan, Afghanistan, and Baluchistan, 'reveals a dozen examples of regions that could experience a future earthquake of magnitude more than 8'.

Because the population of the Ganga basin is larger than at any time in history, any future massive earthquakes in the Himalayas could have a much greater impact on people than the recent tsunami, the scientists warned.

According to the US scientists, the western Himalayas may be in a stress state somewhat similar to the Andaman plate boundary prior to 2004.

"Although we have no historical examples of simultaneous rupture of contiguous segments of the Himalayas, we would, given the recent M-9 earthquake on India's Andaman boundary, be foolish to ignore the possibility of a similar great earthquake in the Himalayas," the US scientists said.

Harsh Gupta, former director of NGRI who recently predicted an earthquake in Koyna before December 2005, however, refused to guess when the next Himalayan quake would occur.

He said he did not subscribe to the seismic gap theory according to which a region that has remained quiescent for long is ripe for rupture.

Negi lamented the lack of seismic policy and a professional disaster management system in India.

"Seismology is not high priority for India despite the fact the entire Himalayan region is under the earthquake shadow," he told PTI. 

"We have just 40 to 50 seismologists in this country against 7000 in China."