Washington: A major earthquake, of magnitude 8 or greater, may strike Jammu and Kashmir , endangering the lives of as many as a million people, latest geologic mapping in the Himalayan mountains of the state suggests.


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Scientists have known about the Riasi fault in Jammu and Kashmir, but it was not thought to be as much as a threat as other, more active fault systems.


However, following a magnitude 7.6 earthquake in 2005 on the nearby Balakot-Bagh fault in the Pakistan-occupied Kashmir - which was not considered particularly dangerous because it was not on the plate boundary - researchers began scrutinising other fault systems in the region.


They found that the Riasi fault has been building up pressure for some time, suggesting that when it does release or "slip," the resulting earthquake may be large - as much as magnitude 8.0 or greater.


"What we set out to learn was how much the fault has moved in the last tens of thousands of years, when it moved, and how different segments of the fault move," said Yann Gavillot, lead author on the study who did much of the work as a doctoral student at Oregon State University in the US.


"What we found was that the Riasi fault is one of the main active faults in Kashmir, but there is a lack of earthquakes in the more recent geologic record.


"The fault hasn't slipped for a long time, which means the potential for a large earthquake is strong. It's not a question of if it's going to happen. It's a matter of when," said Gavillot.


There is direct evidence of some seismic activity on the fault, where the researchers could see displacement of the Earth where an earthquake lifted one section of the fault five or more meters - possibly about 4,000 years ago.


Written records from local monasteries refer to strong ground-shaking over the past several thousand years, researchers said.


However, they do not have much evidence as to how frequent major earthquakes occur on the fault, or when it may happen again.


"The Riasi fault is not prominent on hazard maps for earthquake activity, but those maps are usually based more on the history of seismic activity rather than the potential for future events," said Andrew Meigs, a geology professor in OSU's College of Earth, Ocean, and Atmospheric Sciences and co-author on the study.


"In actuality, the lack of major earthquakes heightens the likelihood that seismic risk is high," said Meigs.