US researchers say recent satellite imagery shows that North Korea has begun dismantling facilities at its nuclear test site.

An analysis today by the 38 North website said commercial imagery taken last week of the Punggye-ri nuclear test ground showed several operational support buildings had been razed, and rails for mining carts apparently removed.

North Korea said it will dismantle the site between May 23 and 25 in the presence of local and international media. It now seems work has already begun.

“Other more substantial buildings around the facility remain intact, including the two largest buildings at the Command Center, and the Main Administrative Support Area. Moreover, no tunnel entrances appear to have yet been permanently closed,” the analysts report.

Their continued presence may indicate they are intended for an international spectacle.

The Korean Central News Agency (KCNA) announced that the dismantlement would be witnessed by foreign journalists and would involve the “collapsing all of its tunnels with explosions, blocking its entrances, and removing all observation facilities, research buildings and security posts.”

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The document notes reports sourced from US intelligence agencies that instrumentation and electrical cabling had also been removed, although this is not evident from the satellite photographs.

The site was used for six underground nuclear test explosions. But, last year, the largest of these triggered speculation that the mountain itself had suffered damage to its foundations. There were fears of collapse, and the spread of a radioactive dust cloud.

MOVING MOUNTAINS

Analysis of new satellite-based remote sensing technology has confirmed the structure of the mountain beneath which North Korea has been conducting its nuclear tests had changed.

The mountain’s shape has been flattened. It’s also half a metre shorter.

International interest focused on Mt Mantap in September last year after satellite imagery revealed large-scale landslides on its slopes after the most recent below-ground nuclear test.

Speculation was rife that the bomb — the most powerful detonated by North Korea yet — had vaporised an enormous chamber at its base. This, combining with similar chambers from five earlier tests, caused the mountain to ‘sag’.

The new study, reported by the AAAS journal Science, says this would have required the equivalent of 120-300,000 tons of dynamite.

A new paper in Science combines seismic measurements and satellite data to track the shifts of Mt. Mantap, home to a North Korean nuclear testing site: https://t.co/6H59oqUhNJ pic.twitter.com/f1kFHI1TSe — Science Magazine (@sciencemagazine) May 11, 2018

The detonation, it says, was also at a relatively shallow depth.

“To better understand characteristics of this last nuclear test blast, Teng Wang and colleagues applied an innovative combination of seismic waveform data and satellite data from the German satellite TerraSAR-X, a tool to better grasp vertical displacement,” their statement reads.

Their modelling was used to identify the location of the latest blast, placing it 450m beneath Mt Mantap’s peak. The aftershock which was detected by seismologists last year and fuelled speculation of the mountain’s collapse has been identified as coming from a location 700 metres south of the main event.

“In further modelling incorporating realistic topography, the researchers estimated the yield from the explosion to be as great as 209 kilotons, larger than most previous estimates,” the statement reads.