PARIS • Large quakes in Nepal this year only partially relieved stress on a major Himalayan fault line, and chances of a big tremor are as high as before, researchers said.
University of Cambridge professor Jean-Philippe Avouac, who co-authored studies published simultaneously in the journals Nature Geoscience and Science, said there was enough "strain to drive a large earthquake in western Nepal".
"This was the case before the Gorkha earthquake, and it hasn't changed significantly since," he said on Thursday, adding that the risk of another one was "not lower" - although not significantly higher.
The Gorkha district was near the epicentre of a 7.8-magnitude tremor on April 25, the worst in Nepal in more than 80 years. A 7.3-strong aftershock followed on May 12.
The twin quakes killed more than 8,700 people, triggered landslides and destroyed half a million homes, leaving thousands in need of food, clean water and shelter.
However, most lodges and hiking trails near Mount Everest suffered only minimal damage, according to a government-commissioned report that could offer some hope to Nepal's battered tourism industry.
The paper by California-based engineering firm Miyamoto noted that Nepal must carry out a detailed assessment of the region after the ongoing rainy season, to manage further risks to trekkers.
The government commissioned the report into the safety of the Everest region and the Annapurna trekking circuit after Western insurance firms increased premiums for travellers following the quakes.
Tourism, which makes up about 4 per cent of Nepal's economy, could shrink by 40 per cent from levels last year, officials said.
The country rests on a major fault line between two tectonic plates - one that bears India pushing north and east at a rate of about 2cm a year against the other, which carries Europe and Asia.
This process along the Main Himalayan Thrust (MHT) fault created the Himalayan mountain range and triggers quakes when strain built up along the fault gives way periodically, thrusting the overlying land mass upwards and outwards.
In the recent disaster, an area about 150km long and 50km wide gave in after decades of pressure.
Experts say the capital Kathmandu shifted over 1.5m southwards and was raised by nearly a metre. Mount Everest is estimated to have moved 3cm to the south-west.
The April 25 earthquake started north-west of Kathmandu, and then spread eastwards along the fault for about 140km, running underneath the city but not reaching the land surface.
The fault had remained "locked" for 20 years without any release of stress, according to the paper published in Nature Geoscience.
The quakes this year transferred unreleased pressure into the western and shallower parts of the Earth's crust.
"The locked portion of the MHT west of the 2015 event calls for special attention," the paper cautioned - noting a 800km-long stretch where there had been no large quake for more than 500 years.
Prof Avouac added: "We will have at some point a large earthquake in western Nepal, but the probability of it happening today is not significantly larger than it was before the Gorkha quake."
AGENCE FRANCE-PRESSE, REUTERS