North Korea might have tested another nuclear rocket after satellite image analysis shows some suspicious activity on Sohae Satellite Launch Station.

This speculation arose during the Workers' Party in North Korea. South Korea and the US started to notice that nuclear tests and missile launches took place on significant political dates in the country. According to Yahoo News, the US-Korea Institute at John Hopkins University were the once who noticed the suspicious activity in the country.

They noticed crates on the launch pad and vehicles near the fuel and oxidiser buildings. Aside from that, they also noticed some movement on their vertical engine test stand. However, the Institute admitted that there are covered areas on the station like the gantry tower and assembly structures, which made it unclear if there were really preparing a launch that day.

BBC News reported that scientists use seismometers to find out if the blast came from a nuclear blast. They said that everything has a distinct vibration. They explained that Earthquakes have quick and sharp pressure waves that are followed by shear and surface waves.

On the other hand, landslides has the vibration of debris rolling down slopes while volcanic eruptions has the blast of breaking rocks caused by lava.

Explosions can be identified through high-intensity seismic energy that happens in brief durations. This was first discovered in the Cold War when the United States funded a research to use seismology to track the weapons development program of the Soviet Union. Since then, scientist all over the globe used seismology to track down explosions further differentiating the difference of vibrations caused by an earthquake and vibrations caused by explosions.

The first nuclear test in Korea happened on Oct. 9, 2006 in an underground detonation site which has a low yield and was considered a failure by most people. The most recent test happened last month when they tested a high-powered rocket engine which the South believes was targeted on the US east coast.