Test Today 1

More than a week later, researchers are still puzzling over what caused that extra release of seismic energy—and what it says about North Korea’s nuclear-testing site, or the risks of a larger radiation leak.

A number of theories have emerged to explain the second event, ranging from a tunnel collapse or a landslide to a splintering of the rock inside Mount Mantap, the testing site.

On September 13, the South Korean Nuclear Safety and Security Commission in Seoul announced that several ground- and sea-based monitoring stations downwind of the test site had detected the radioactive isotope xenon-133, an indicator of a nuclear test.

If so, that could lead to contamination of the mountainous area by radioactive material.

More than a week later, researchers are still puzzling over what caused that extra release of seismic energy—and what it says about North Korea’s nuclear-testing site, or the risks of a larger radiation leak.

A number of theories have emerged to explain the second event, ranging from a tunnel collapse or a landslide to a splintering of the rock inside Mount Mantap, the testing site.

The characterization of landslides and rock bursts could help researchers to assess how unstable Mantap is.

Monitoring stations in South Korea have already picked up minute levels of radiation from the test.

If so, that could lead to contamination of the mountainous area by radioactive material.

The US Geological Survey (USGS) determined the magnitude of the seismic event associated with the nuclear explosion at 6.3, whereas the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) in Vienna calculated it at 6.1 on the basis of a separate analysis.