A mega earthquake that rocked Kathmandu in 1255 wiped out a third of the city's population and killed then King Abhaya Malla, was of a kind that may return to the Himalayan region, seismologists have said.

The news comes as experts from Nepal, France and Singapore mapped deposits of river sediment displaced along part of the fault line where the Indian subcontinent converges into the Asia tectonic plate at up to 50 millimetres per year, AFP reported.

"With the help of carbon dating, they found that the soil movement in one place was caused by a huge quake that coincided with the great event of July 7 1255. More than six centuries later, there was another surface-breaking event, correlating to a magnitude 8.2-event in 1934," said the report.

Experts say that such ruptures are not only extremely violent, they also tend to release most or all of the built up strain (energy).

The study, published in the journal Nature Sciences, says that it might take centuries for similar strain to accumulate and lead to another break, if the evidence of the surface turnover is a guide.

"This long time-span is worrying as the previous event may be undocumented or poorly understood because it is so ancient," the report adds.

Scientists have not ruled out the possibility that other potential 'monsters' –– soil ruptures waiting to happen — could be lurking elsewhere on the fault, as no-one has looked for the evidence for them.

"Two great earthquakes 679 years apart contributed to the frontal uplift of young river terraces in eastern Nepal," says the paper, published in the journal Nature Geoscience.

"The rare surface expression of these earthquakes implies that surface ruptures of other reputedly blind great Himalayan events might exist." nepalnews.com