One Year Ago — NORTH KOREA H-Bomb : First estimate of the Yield

“The institute recently succeeded in making a more developed nuke. Kim Jong-un watched an H-bomb to be loaded into a new ICBM (intercontinental ballistic missile).”

KCNA — North Korea State News Agency (September 3 2017)

“Based on the similarity of the seismic data between 3 September 2017 event and North Korea’s previous nuclear tests, we confirm that 3 September 2017 event is a nuclear test in nature. We have determined that North Korea’s 3 September 2017 nuclear test occurred at UTC 2017/09/03 03:30, (2017/09/03 12:00 local time), at the location of (41°17’53.52”N, 129°4’27.12”E), with an estimated yield of 108.3±48.1 kt.”

USTC  — Lianxing Wen’s Geogroup

September 4 2017 — North Korea said on Sunday (September 3 2017) it has developed a more advanced nuclear weapon that has “great destructive power” and leader Kim Jong Un inspected a hydrogen bomb that will be loaded on a new intercontinental ballistic missile (ICBM). Considering the magnitude of the event as reported by the US Geological Survey,  I have estimated — in first approximation — the yield of the device at about 126.8 kilotons of TNT equivalent. A well-known Chinese research group has since provided a similar estimate. However the magnitudes reported by South Korea and NORSAR are much lower. UPDATE (September 6 2017)  — At this point, there seems to be a consensus that the magnitude (Mb) of the event is at least 6.0 and possibly as high as 6.4. Follow us on Twitter: @INTEL_TODAY

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Pyongyang said it had tested a hydrogen bomb – a device many times more powerful than an atomic bomb.

Analysts say the claims should be treated with caution, but its nuclear capability is clearly advancing.

Initial reports from the US Geological Survey put the tremor at 5.6 magnitude with a depth of 10km (six miles) but this was later upgraded to 6.3 magnitude at 0km. This would make it the North’s most powerful nuclear test to date.

Bruce Bennett, a defence analyst at public policy group the Rand Corporation, told the BBC that the size of the tremor was significant.

“If it really does prove out to be 6.3, that’s a very big weapon, much bigger”.

“It’s still not a true hydrogen bomb but it’s certainly much closer to that than anything they have ever done before.”

CTBTO Preliminary Statement

The Director of the CTBTO has issued the following statement:

Vienna, 3 September 2017

“Our monitoring stations picked up an unusual seismic event in the Democratic People’s Republic of Korea (DPRK) today at 03:30 (UTC). So far over 100 of our stations are contributing to the analysis. The event seems to have been larger than the one our system recorded in September last year and the location is very similar to that event. Our initial location estimate shows that the event took place in the area of the DPRK’s nuclear test site. ( 03-SEP-2017 03:30:06 LAT=41.3 LON=129.1 )

Our experts are now analysing the event to establish more about its nature and we are preparing to brief our Member States today in Vienna.

“If confirmed as a nuclear test, this act would indicate that the DPRK’s nuclear programme is advancing rapidly. (…) “

The Facts

The USGS is reporting a Magnitude 6.3 event near the site where North Korea has detonated nuclear explosions in the past.

Magnitude       uncertainty
6.3 mb               ± 0.0

Location                            uncertainty
41.343°N 129.036°E      ± 6.1 km

Depth     uncertainty
0.0 km   ± 1.7

Origin Time
2017-09-03 03:30:01.940 UTC

Yield of the explosion

Based on Nevada underground explosion tests conducted in granite, the magnitude of body waves is proportional to the logarithm of the yield in kilotons:

Mb = 4.26 +0.97 log (Y).

The yield T is expressed in kilotons unit. A kilotons is equivalent to 1,000 tons of TNT.

According to the above equation, the magnitude reported by the US Geological Survey translate in a yield of 126.8 kilotons of TNT equivalent.

Data from South Korea

South Korea Joint Chiefs of Staff (JCS) said it detected a 5.7-magnitude earthquake around 12:39 p.m. at North Korea’ nuclear test site in Punggye-ri, Kilju-gun, North Hamgyong Province. It said the earthquake was artificial. The Korea Meteorological Administration (KMA) also detected the artificial seismic event.

Both the JCS and KMA initially announced that the quake had a magnitude at 5.6 but corrected it to 5.7.

The magnitude reported by the JCS and KMA is significantly lower than the 6.3 published by the USGS. No exact yield was announced so far.

“I can’t predetermine, but it is believed to be 100 kilotons at the most,” said Rep. Kim Young-woo, who chairs the National Assembly National Defense Committee.

However, based on the above equation, I estimated that the magnitude reported by the JCS and KMA translate in a yield of 30.5 kilotons of TNT equivalent.

UPDATE (September 6 2017)  — At this point, there seems to be a consensus that the magnitude (Mb) of the event is at least 6.0 and possibly as high as 6.4.

South Korean Government’s  detected a 5.7 magnitude earthquake.

 “N. Korea’s apparent sixth nuke test estimated to have yield of 100 kilotons: lawmaker”

NORSAR Seismology Center reported a magnitude 5.8 tremor.

 “Large nuclear test in North Korea on 3 September 2017

The German Federal Institute for Geosciences and Natural Resources says it detected a 6.1 tremor.

 “BGR registers a presumed nuclear test in North Korea

The Japan Meteorological Agency also detected a 6.1 magnitude tremor.

 “North Korea tests most powerful nuclear bomb yet”. ABC. CNN, Scripps National Desk. September 3, 2017.

USGS: Initial reporting from the US Geological Survey (USGS) first claimed the magnitude to be 5.2, but quickly upgraded the event to magnitude 6.3.

“M 6.3 Explosion – 22km ENE of Sungjibaegam, North Korea

The China Earthquake Administration also detected a 6.3 magnitude earthquake.

 “China Earthquake Administration detects ‘suspected explosion’ in North KoreaWen, Philip (September 2, 2017) — Reuters

The Geophysical Service of the Russian Academy of Sciences registered a 6.4 magnitude earthquake.

“North Korea likely to have conducted another nuclear test — Japanese TV”. TASS. Government of Russia. September 3, 2017.

CTBTO — So far, no final result has been released. The following message was posted:

 “The event seems to have been larger than the one our system recorded in September last year and the location is very similar to that event. Our initial location estimate shows that the event took place in the area of the DPRK’s nuclear test site. ( 03-SEP-2017 03:30:06 LAT=41.3 LON=129.1 )”

CTBTO Executive Secretary Lassina Zerbo on the unusual seismic event detected in the Democratic People’s Republic of Korea

However, the Exec Secretary of the Comprehensive Test Ban Treaty Organization (CTBTO) tweeted a few preliminary data. The first analysis gives magnitude 5.8.

https://twitter.com/SinaZerbo/status/904206338099748866

Currently, the CTBTO webpage displays the following information:

“CTBTO’s monitoring stations picked up an unusual seismic event in the Democratic People’s Republic of Korea (DPRK) on 3 September 2017 at 03:30 (UTC). Over 100 of our stations contributed to the analysis. The magnitude of the event was 6.0. Review of the data is still ongoing. The event seems to have been larger than the one our system recorded in September last  year and the location is very similar to that event. Our initial location estimate shows that the event took place in the area of the DPRK’s nuclear test site.”

In first analysis, these magnitude translate in yields ranging from 30 kT (mb = 5.7) to 160 kT (mb = 6.4). However, a detailed calculation — taking into account the exact depth of the explosion — could yield to a significantly higher yield. More about this in a following post…

I asked Professor Jeffrey Park — Yale University — what he makes of these numbers.

“Mb=6.3 is the USGS estimate. The SK estimate was a quick estimate I think, but I don’t have direct info about it.

I know that the USGS estimate will have been calibrated against the waveforms of previous NK explosions.”

“An explosion with Richer Magnitude 6.3 is much larger than typical for a fission device.

It does not mean that the device can be put on a missile, but the size suggests that NK has fabricated a working fusion device.”

As a prelude to the event, Korean Central Television (KCTV) posted images the day before the test of Kim Jong Un visiting the “Nuclear Weapons Institute” to see what was described as a two-stage hydrogen warhead for the Hwasong-14 inter-continental ballistic missile (ICBM).

That announcement claimed that the warhead was designed to have a variable yield, “the explosive power of which is adjustable from tens kilotons to hundreds kilotons, is a multi-functional thermonuclear nuke with great destructive power which can be detonated even at high altitudes for super-powerful EMP attack according to strategic goals.” [38 NORTH]

It should be noted that another seismic event, magnitude 4.6, was detected exactly 8.5 minutes after the noon event. It is not clear at the moment what may have caused this secondary tremor. — END of UPDATE

North Korea claims new bomb has ‘great destructive power’

REFERENCES

North Korea nuclear test: Hydrogen bomb ‘missile-ready’ — BBC News

N. Korea claims successful H-bomb test for ICBM  — Korea Times

North Korea’s nuclear bomb: Can we work out its power? — BBC

High-precision location and yield of North Korea’s 2013 nuclear test
GEOPHYSICAL RESEARCH LETTERS, VOL. 40, 2941- 2946

Making Yield Estimates — Arms Control Wonk

The Seismic Signal Strength of Chemical Explosions  — Bulletin of the Seismological Society of America, Vol. 88, No. 6, pp. 1511-1524, December 1998

North Korea’s 3 September 2017 Nuclear Test Location and Yield: Seismic Results from USTC — Lianxing Wen’s Geogroup

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NORTH KOREA Claims to Have Successfully Tested H-Bomb [First estimate of the Yield]

NORTH KOREA Claims to Have Successfully Tested H-Bomb [UPDATE — First estimate of the Yield]

One Year Ago — NORTH KOREA Claims to Have Successfully Tested H-Bomb [First estimate of the Yield]

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