Posted September. 07, 2017 07:34,
Updated September. 07, 2017 08:07
Naturally occurring earthquakes are divided into three types -- tectonic, volcanic and collapse earthquakes. Most large-scale earthquakes are tectonic ones caused by transformation in fault lines. Volcanic activities can also cause quakes, and so can the collapse of a giant underground cave. Volcanic and collapse earthquakes are relative smaller in scale than tectonic ones. A tremor caused by shocks from an underground nuclear test is called an artificial earthquake. However, a secondary quake caused by underground tunnels caving in following a nuclear test is a collapse earthquake.
Just 24 minutes after North Korea’s sixth nuclear test launched on Sunday, China said a magnitude 4.4 collapse earthquake occurred at the test site about eight minutes and 30 seconds after the test. Considering that no collapse quake was detected after the first five nuclear tests, Sunday’s earthquake is indicative of how powerful the latest nuclear test was. South Korea’s Korea Meteorological Administration seemed to have been unprepared for observation of a collapse earthquake. It took two days for the agency to announce its detection of seismic waves presumed to be a collapse after analyzing the waves broken down into high and low frequencies.
A collapse earthquake following a nuclear test indicates the possibility of radioactive leakages that could directly affect the safety of the people living in South Korea. Therefore, the meteorological agency is under fire for its belated confirmation of a collapse earthquake. The North’s nuclear tests conducted in Pungye-ri in North Hamgyong Province near the northern tip of North Korea. The site is more than 400 kilometers away from the demilitarized zone. The radioactivity levels in South Korea measured by the Nuclear Safety and Security Commission is the same as usual. However, North Koreans living close to the site could be affected.
Satellite imagery disclosed by 38 North, a North Korean affairs website run by the U.S.-Korea Institute at Johns Hopkins University's School of Advanced International Studies, showed landslides and other disturbances at the site that were more widespread than any of the five nuclear tests North Korea previously conducted. No signs of a tunnel collapse could be detected because of the low resolution of the imagery. We will have to wait for the results of analyses of higher resolution satellite imagery. If there are widespread topographical changes, it is too early to feel relieved because of the possibility of additional collapses.