Washington D.C.: The Gorkha earthquake, that struck Nepal on April 25, 2015, the magnitude 7.8 jolt, which was very shallow (only 15 km underground), caused a tremendous amount of damage in Kathmandu.
But it didn’t rupture the Earth’s surface, signifying that only part of the fault had slipped, below-ground.
In the following days, even the after slip, post-earthquake movement, produced little surface evidence of continued movement.
That meant only one of two things could be happening: either the part of the fault that had not moved was experiencing a slow-slip event, a slow-motion earthquake, or it remained completely locked, accumulating further strain in that segment of the fault.
A new study says, it is likely the latter.
Following the earthquake, an international team of scientists quickly deployed a series of GPS receivers to monitor any movements.
They also relied on InSAR, interferometric synthetic aperture radar, to look for changes to the Earth’s surface. They found there had been 70 mm (2.75 inches) of afterslip north of the rupture and about 25 mm (1 inch) of afterslip to the south of the rupture.
But scientists estimate there’s about 3.5 meters (11.5 feet) worth of strain built into this fault, which those post-earthquake movements did nothing to alleviate.
Historical earthquakes in the region, in 1803, 1833, 1905 and 1947 also failed to rupture the surface of the Himalayan frontal faults and they, too, experienced a lack of afterslip or large subsequent earthquakes.
That, according to the team’s research, means there’s significant strain throughout the region.
And this region remains vulnerable to earthquakes, not only because of its geography, but because of its architecture and development patterns. While this 2015 earthquake killed 8,000 people, left tens of thousands homeless and destroyed parts of Kathmandu, the amount of strain built up in the faults, if released suddenly, could do much more damage in this part of the world.
That’s why Mencin and his colleagues are already at work on their next paper, which they hope might help identify patterns across the entire Himalayan front.
The study has been published in Nature Geo science.

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