A mega-quake in 1255 that wrecked the Nepalese capital, wiped out a third of the population of Kathmandu Valley and killed the country's monarch, King Abhaya Malla, was of a kind that may return to the Himalayas, seismologists have reported.
Experts from Nepal, France and Singapore mapped deposits of river sediment displaced along part of the fault line where the Indian subcontinent pushes into the Asia tectonic plate at a rate of up to 50mm per year.
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.
The finding is important because until now there had been no evidence of surface ruptures from the collision of these plates.
Surface ruptures are very violent and also tend to release most or all of the accumulated strain. "Blind" quakes are ones that do not break the surface, and tend to be more frequent.
The study, published in the journal Nature Geoscience and released on Sunday, says it probably takes centuries for the strain to accumulate before another major quake occurs. Such a long timespan is worrisome, because previous events may be undocumented or poorly understood.
The scientists do not rule out the possibility that other potential monster quakes could be lurking elsewhere on the fault, as no-one has looked for the evidence for them.