Update – 11:21 EST: North Korea has announced it tested a hydrogen bomb

Latest – 10:02 EST: North Korea has declared it will issue a special statement at 12:00 noon Pyongyang time

Correction: NK News intelligence director John Grisafi was originally quoted saying the magnitude of the test was lower than that of the third test. This statement was made in error due to conflicting figures and has been revised to state that the fourth test’s magnitude was similar to the third and higher than the first two. The statement regards the original reported magnitude. The magnitude of the fourth test has since been revised down.

An artificial earthquake measuring 5.1 on the Richter scale has struck North Korea, triggering seismological detectors.

The epicenter of the quake appears to be in central part of North Hamgyong province, near the border of Ryanggang. The Punggye-ri nuclear test site is located in this area. According to world-earthquakes.com the depth of the quake was 10km.

Small earthquakes in North Korea could indicate a nuclear test, which are conducted underground.

“It seems like an artificial earthquake, we are figuring out the exact scale and point of the earthquake,” the Korean Meteorological Association (KMA) told NK News.

“The magnitude, 5.1 is similar to the third test and higher than the first two tests,” NK News intelligence director John Grisafi said.

News of the development comes after satellite imagery analysis at the 38 North website late last year identified activities at the Punggye-ri nuclear test site potentially consistent with a fourth nuclear test.

In mid September, imagery suggested North Korea was building a new tunnel for nuclear testing that could “be related to anything from maintenance work to preparations for another nuclear test,” the website said at the time.

A subsequent December 2 analysis on the Washington DC based site said that “recent commercial satellite imagery indicates new activity at North Korea’s Punggye-ri nuclear test site, the location of Pyongyang’s previous three nuclear detonations.”

North Korea has previously conducted nuclear tests on October 9, 2006, May 25, 2009, and February 12, 2013, with explosive yields of less than one kiloton, 2-4 kilotons and 6-7 kilotons, respectively.

The earthquake follows a smaller one in China’s Heilongjiang province three days ago, which measured 4.9 on the Richter scale.

Eom Sang-yoon, a researcher at the Sejong Institute, told NK News that there should’ve been signs beforehand of preparation for a nuclear test, such as movements of trucks, but such signs were not spotted or reported in his knowledge.

38 North, however, has recently reported activity at the Punggye-ri site. Information on such activity and movements is not always fully up-to-date as it is limited to updates of satellite imagery. Additionally, North Korea has shown a capability in the past, such as the December 2012 launch of the Unha-3 space rocket and Kwangmyongsong-3 Unit 2 satellite.

South Korean news agency Yonhap has reported that North Korea will declared “special important report” at 12:30 pm. Blue House has organized emergency meeting of National Security Council at noon.

“Seems that the 12:30 (Pyongyang time) announcement to come will confirm it. Let speculation rage until then, but I’ve never known Pyongyang to televise a special report to deny something,” Christopher Green, former editor of Daily NK told NK News.

“Ramifications are hard to predict, but I imagine it won’t improve their international standing at all,” he continued.

“Ramifications? What ramifications? a bit of noise, and perhaps another UN Security Council resolution which will change little or nothing, but nothing of substance,” Professor Andrei Lankov at Kookmin University told NK News.