“It is clear that the quake wasn’t caused by an artificial explosion.”
South Korea Meteorological Administration (Anonymous)
“This event occurred in the area of the previous North Korean Nuclear tests. We cannot conclusively confirm at this time the nature (natural or human-made) of the event. The depth is poorly constrained and has been held to 5 km by the seismologist. The Air Force Technical Applications Center (AFTAC) is the sole organization in the U.S. federal government whose mission is to detect and report technical data from foreign nuclear explosions.”
USGS — September 23 2017
CTBTO Analysts are looking at an unusual seismic activity of “small magnitude” in North Korea timed at 23-SEP-2017 08:30 UTC. An artificial explosion seems unlikely. Follow us on Twitter: @INTEL_TODAY
FINAL UPDATE September 25 2017 — CTBTO analysts have compared the 2nd event September 3 with with the two events of September 23 2017.
The location of these four events — Sept. 3 at 3:30 & 3:38 UTC and Sept. 23 at 4:43 & 8:29 UTC — are indicated in the above picture with their associated error ellipse. The analysis confirms that the September 23 events have a tectonic origin. They are clearly NOT man-made.
END of UPDATE
The US Geological Survey (USGS) says it can not yet make a judgment as to the cause. The USGS seismologists assessed it as having a depth of 5 km.
“We cannot conclusively confirm at this time the nature (natural or human-made) of the event,” it said.
The USGS provides the following data:
Mb = 3.5
22km ENE of Sungjibaegam, North Korea
2017-09-23 08:29:17 UTC
5.0 km depth
At this point, the most reasonable cause of these earthquakes is some collapses at, or near, the testing site, quite possibly connected to the September 3, 2017 test.
Please, note that the time appears to be random and that the depth is much lower than the known location of the test site tunnels, less than 1km.
These data and the low value reported for mb confirm my early suspicion that these events are NOT the result of a nuclear explosion. They may however be an ‘aftermath’ of the September 3 nuclear test.
UPDATE September 23 2017 11:49 GMT — Worldwide nuclear monitoring agency CTBTO says analysts have detected two seismic activities in North Korea which are unlikely to be manmade.
Two Seismic Events were detected around 08:29 UTC. They are unlikely Man-made. According to CTBTO Executive Secretary, these events are rather similar to the “collapse” event wich occurred 8.5 mins after the DPRK 6th test on September 3rd 2017. Analysis is ongoing. Stay tuned. — END of UPDATE
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The China’s earthquake administration first reported that a magnitude 3.4 earthquake has been detected in North Korea.
The earthquake has occurred near a North Korea nuclear test site.
Chinese seismologists suspect an explosion. [Comment: Perhaps because of the measured depth (around 0 km) or maybe because it occurs at a specific time such as exactly 08:30 UTC.]
South Korea says that it could be a natural earthquake, rather than one caused by a nuclear test.
North Korea carried out its sixth nuclear test on 3 September 2017. The magnitude was much higher, about 6.3 according to current estimates.
If true, the test would almost certainly be a “fizzle” with a yield less than a kilotons. So far, the lowest yield was mb = 4.0 (Yield = 0.5 kT) on the first test of October 9 2006.
Time & Location
“Korean Peninsula unusual #seismic activity: LAT=41.36 LON=129.76 mb=3.5 About 50 km from prior tests. #CTBT Analysts investigating,” CTBTO Executive Secretary Lassina Zerbo said in a Twitter post.
Tremors detected in North Korea raising fears of another nuclear test
A Nuclear Test Monitoring Agency has reported two seismic events in North Korea. Both the CTBTO Agency and South Korea said early analysis suggested it was unlikely the tremors were man-made.
South Korea’s meteorological agency said early indications suggested it was a natural earthquake because no sound waves specific to man-made tremors had been identified. The agency put the tremor at magnitude 3.0.
N. Korea claims successful H-bomb test for ICBM — Korea Times
High-precision location and yield of North Korea’s 2013 nuclear test —
GEOPHYSICAL RESEARCH LETTERS, VOL. 40, 2941- 2946
NORTH KOREA — Small Artificial Earthquake
NORTH KOREA — Small Artificial Earthquake Detected? [UPDATE]