More data is becoming available on Monday’s nuclear test. NORSAR has published the waveform data from two of their stations. The primary wave is very noticeable and sharp, which indicates a man-made explosive event (earthquakes tend to brew a while before really making noise).
The shear-wave seems to come in shortly thereafter, giving a distinct peak. I like to think of the difference between p and s-waves as flash and thunder. The p-wave comes in fast (in air it travels at the speed of sound) whereas the s-wave rumbles in afterwards. Now, I only have these two datasets, and no other forms, but the signal from ARCES looks peculiar to me. About 10 seconds in there is a sharp fluctuation in the peak-to-peak amplitude, which isn’t visible in the NOA readout. I’ve heard that the seismologists at the IMS division is confused about some of the data as well, but I’m not sure if it’s that peculiarity that they’ve focussed on.
When the s-waves hit, you’ll notice some refraction.
If you want to check that these forms match the time of the test, please consult the p-wave travel time image below.
Updated: those interested in antipodal seismometry (see Geoff’s post below) might find the image interesting for other reasons.
Most interestingly, the CTBTO has published the error ellipses and visualised them in Google Earth. As you can see, both error ellipses define a search area well within the 1,000 sq. km. maximum search grid stipulated by the treaty. In other words, if the CTBTO hypothetically were to conduct an OSI, they would have a pretty good idea where to start.
But these are only some of the goodies to come. I got an e-mail from Sean O’Connor this morning, who wrote that he’s found the likely location of at least two additional sites in the area. He’s going to publish his findings on IMINT & Analysis quite soon.
The yield estimate is still highly uncertain, but is likely to be below 4-8 kT range that has been reported in mainstream media so far. But given the discussion in my last thread, I’m attaching this nice Mb – Yield graph for the community to have a look at.
Note that using the NTS hard rock formula puts the yield at 1.6 kT, which fits the assessment of the United States.
Finally, the word is that meteorological conditions at the moment are favourable for a first noble gas hit in South Korea, maybe also in Ussurijsk and later in Japan. But that’s for another post.
Sean O'Connor | May 27, 2009
I’ll have something available by the end of the week. I want to annotate everything of interest in the area to give a better idea of the scope of the operation up there.
V.S. | May 27, 2009
It seems that part of the discussion on the
test went to the stealthiness of the
preparations and to the fact that almost
everyone was clueless
about the imminence of a nuclear test.
Charged to look into it, from an open
sources point of view, the only piece of
news that could be a hint prior to the
test is this (that I found with the help
of the Disarmament Digest).
http://www.google.com/hostednews/
afp/article/ALeqM5j7IgzNTBPAf05iqKCqxNkTTdwkuA
http://in.reuters.com/article
/worldNews/idINIndia-39807620090522?pageNumber=1&virtualBrandChannel=0
22 May – North Korea appears to be
preparing to test-fire short-range missiles
after banning ships from waters off its
northeast coast, according to a report.
A vehicle mounted with a missile launcher
has been seen moving around for the past two
or three days in an eastern coastal area of
Hamkyong province, South Korea’s Yonhap news
agency quoted a government source as saying.
“Judging from an analysis of the movements,
the North appears to be preparing to test-launch
short-range missiles,” the source
was quoted as saying.
In Tokyo, Japan’s Coast Guard said the
authorities of the DPRK was warning ships
not to pass through waters within
a 130-kilometres (80-mile) radius of
the town of Kimchaek. It said the warning
applied to the hours between 10:00 am (0100 GMT)
and 6:00 pm until the end of the month.
Foreign Minister Hirofumi Nakasone told
reporters Japan was collecting information on the ban.
“I am yet to learn the purpose of the warning,” he said.
A spokesman for the Joint Chiefs of Staff
in Seoul could not confirm the reported vehicle movements.
Note that the seaside port of Kimchaek
is 45 miles NW of the 2006 (and 2009) nuclear
testing site. But everyone focused on the
missile site in the area and to what appeared
to have been short-range missile launch preparations,
and they (we) missed “the big fish”.
Also the time designated by the DPRK authorities
10:00 am could not have been coincidental.
The nuclear test finally
took place at 9:54 am followed by the missile launces.
But on the other hand how could one have guessed before.
Now of course it’s more obvious.
bradley laing | May 28, 2009
http://washingtontimes.com/news/2009/may/28/inside-the-ring-35177217/
Preliminary indications are that the latest test produced a yield of 4 kilotons to 5 kilotons, nearly 10 times bigger than 2006. Final estimates are not expected for several more days, said a U.S. official familiar with reports of the test. A kiloton is the equivalent of 1,000 tons of TNT.
—Claim made on the “Washington Times” website.
sun bin | May 28, 2009
an idea for setting up monitor station. if you know the source (test location) quite precisely (i.e. error is small compared with the wavelength), you can place a few (preferably iso-distant among themselves) probes along the contours in your map above (again, the error needs to be small compared with the wavelength).
you can then analyze (sum up) the signals from these probe. they will capture shock wave IN PHASE (while noises are not in phase) and your results will be fairly good. this will be equivalent to (or even better than for nearby contours) the antipodal measure.
blumps | May 28, 2009
more waveforms from the Russian geophysical service: http://www.ceme.gsras.ru/cgi-bin/info_quake.pl?mode=1&id=127
these are for the 2006 event:
http://www.ceme.gsras.ru/cgi-bin/info_quake.pl?mode=1&id=86
FOARP | May 28, 2009
One thing I still don’t understand: how come the Russians still insist that the blast was 10-20 KT? The CTBTO have stations in Russia, and their seismic data agrees with that detected elsewhere, so what’s with the Russians?
Zak Johnson | May 28, 2009
So there has been some big news at the CTBTO that the press hasn’t picked up on yet. The latest press release included the following:
“In addition, they also identified simultaneous signals with earthquake–like characteristics.”
That means that there were multiple sesimic signals from the event that potentially could have jumbled the yield estimate.
Check out the press release here:
LINK
Major Lemon | May 28, 2009
multiple sesimic signals are really to be expected as the shock waver reverberates through the rock, sometimes part of the cave created by the blast collapses.
Andreas Persbo | May 28, 2009
In haste: one hypothesis I’ve heard is that a small conventional explosion triggered an earthquake like event. But I don’t see that in the waveforms at all. But then again, I’m not a trained seismo.
Thanks for the Russian data. Very useful.
J House | May 28, 2009
Gee, The S Koreans must feel better now that we have established that the yield was below 4-8 kilotons.
I would imagine that would leave a good part of Seoul still inhabitable.
Andreas: A bit of irony is always healthy, but do remember that we’re wonks here. We like the meaningless details
Gridlock | May 28, 2009
Don’t the Russians (usefully, I suppose) stick to whatever yield the NORKs tell them in advance they’re setting off? Face saving and all.
Wasn’t the Russian line last time similarly fast out of the blocks and even more disconnected from the reality as measured scientifically?
George William Herbert | May 28, 2009
Major Lemon:
As a rule, unless the test is in very hard rock, there’s almost always at least a partial collapse of the cave. Sometimes that’s the roof spalling off and falling down, sometimes a chimney forms and rock fractures upwards and falls downwards until you have enough fractured rock that the volume expansion going from solid to boulders equals the volume of the direct cavity.
Caging the Dragon and explosives engineering texts are good places to look for more info on this.
Yossi | May 29, 2009
You summarized very well this blog’s and part of the arms control community policy. Alas, history teaches us that if the tech people avoid the moral questions, control will be seized by the politicians who are even less capable of handling them.
Andreas: Sorry for publishing your comment so late. Wasn’t my intention.
s | June 1, 2009
I am surprised not to see a discussion of the possibility that the latest explosion was the same size or smaller than the first. If I were a DPRK nuclear designer I would do everything possible to make the seismic signal as large as possible. The Soviet PNE results show a magnitude 4.7 event from an explosion of about 350 tons. It is reported as having been conducted in a “water-filled cavity.” It would be useful for someone trained in seismology to address whether this is a real possibility.