"Despite the continuation of small tremors near Mt. Mantap since North Korea's last nuclear test, tunnel work at the Punggye-ri Nuclear Test Site is still underway," the analysts wrote on 38 North. "These efforts continue to be concentrated at the West Portal, leaving the North Portal…mostly dormant and likely abandoned, at least for the time being. At the West Portal, there has been a consistently high level of activity since North Korea's last nuclear test."
"Activity" includes personnel and vehicles coming and going with loaded mine carts, which suggests that a tunnel is being excavated and expanded.
The three scholars claimed something similar in November: the "significant movement of equipment, mining carts, material and netting" around the West Portal. In other words, the excavation has continued for at least five weeks now.
The North Portal, the scholars noted, seems to have been abandoned due to the damage it sustained in the previous nuclear test, the largest to date. Cave-ins and nuclear contamination are also feared at the site.
Other analysts corroborated 38 North's claims. Ryan Barenklau, CEO and founder of Strategic Sentinel, a DC-based geostrategy group, told IBTimes UK, "The complex is probably unstable seeing how many tremors have been recording, forcing new tunnels to be created. The West Portal area will probably be where the next nuclear tests will be conducted if there are any more to come."
“Overall, the population in this region resides in structures that are extremely vulnerable to earthquake shaking, though some resistant structures exist,” the service said.
Iran sits atop several fault lines, and Tuesday’s quake comes less than a day after a 6.0-magnitude tremor struck the western province of Kermanshah along the border with Iraq.