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| China-Japan-Koreas |
| Seismic evidence points to N-test |
| 2006-10-10 |
| The Yomiuri Shimbun Seismic waves of varying magnitude were detected at a number of locations shortly after North Korea's announced nuclear test Monday. In South Korea, the magnitudes ranged from 3.58 to 3.7, while the United States said the magnitude was 4.2. In Japan, one calculation showed a magnitude of 5.1. Magnitude differences are likely caused by the differences in calculation methods and the location of observation spots. If those different magnitudes estimated by Monday's blast are translated into energy levels, there is more than a 100-fold difference among the measurements. But the force of the blast in North Korea was seen as much smaller than the atomic bombs dropped on Hiroshima and Nagasaki, which had yields of 15 to 20 kilotons. Prof. Katsuyuki Abe at Tokyo University's Earthquake Research Institute said, "Estimated from magnitudes reported in nuclear tests conducted in the past in the United States and former Soviet Union, the power of the blast this time probably was 0.5 to 3 kiloton, only a fraction of the power of the same type of bomb dropped on Hiroshima." Another expert, however, said, "If there is much space in the mine shaft where the test was conducted, the energy [of the blast] may have been absorbed, showing low-magnitude readings." In either case, the blast this time was small if it was a nuclear detonation. But the scale is still more than dozens of times greater than the most powerful conventional weapons. The seismic waves detected differed from naturally occurring earthquakes. The Meteorological Agency first detected primary waves, or P waves, which are weak but fast-traveling waves, at two observation spots on the Okinoshima islands, Shimane Prefecture, about 660 kilometers away from the epicenter. P waves were detected at one time also at eight observation spots in Nagano, which are equipped with high-precision monitors. In earthquakes, P waves are followed by secondary, or S, waves, which cause more powerful shaking. But S waves are only faintly detected in underground nuclear tests. This also was true in this seismic event. Natural tremors also result in complicated P waves due to fault slippage. But this time, as shock waves are believed to have been generated from one point at one precise moment, the blast likely caused only simple P waves. Takeshi Matsumoto, assistant professor at Kyushu University's Institute of Seismology and Volcanology, said, "Judging from the results of the analysis of seismic waves, [Monday's] tremors were no doubt those caused by an artificial explosion." Although a number of experts said Monday's blast was small for a nuclear explosion, Yuji Yagi, assistant professor at Tsukuba University, concluded the power of the blast was equivalent to 25.72 kilotons of TNT. Yagi's analysis did not rely on magnitude readings. Instead, he used data on seismic waves obtained from overseas research institutes and worked out energy levels observed from the explosion. As the testing is believed to have been conducted in an underground mine shaft, Yagi said he estimated the focus of the seismic event was 1.5 kilometers below the surface. The amount of 25.72 kilotons of TNT is close to the figure observed in a nuclear test conducted by Pakistan in May 1998. Yagi said, "It's still necessary to analyze data in detail, but the blast may have been quite powerful." |
| Posted by:john |
| #8 Are you sure the venting isn't Kimmy's flatulance? |
| Posted by: BigEd 2006-10-10 19:02 |
| #7 Since smaller yields are less likely to fuse the surrounding rock and contain the fission products, some venting is expected (unless that mine is really deep). Atmospheric sampling should pick up traces of the Pu. One interesting suggestion is that the purity of the NoKo Pu is quite low.. it is essentially little better than reactor grade stuff (which would give a low yield). |
| Posted by: john 2006-10-10 18:37 |
| #6 And meanwhile it appears there is no evidence at all that any nuclear fission was actually achieved. |
| Posted by: lotp 2006-10-10 18:27 |
| #5 From a CTBT paper For US announced tests, the equation for the line is: mb = 3.92 + 0.81 log Y(kt) (Murphy, 1981) For the Nevada Test Site and other areas of the world with similar geological conditions, we can use this equation to convert between magnitude and yield Unfortunately, we cannot necessarily apply this formula to every area, because different regions transmit seismic waves with different efficiencies. In the western United States there are high temperatures in the upper mantle, and the continent is being pulled apart by plate tectonic motion. Seismic waves travelling through such tectonically active areas are greatly attenuated (their amplitude is reduced), thus producing a relatively small seismic signal. For tectonically stable areas such as eastern North America and Central Asia (including the Soviet UnionÂ’s old test site in Kazakhstan), the relationship between magnitude and yield is: mb = 4.45 + 0.75 log Y(kt) (Ringdal et al., 1992) So, these geniuses are using Soviet Shagan test site coefficients (tectonically stable region) in the Pacific rim (hardly). And the press laps this all up... |
| Posted by: john 2006-10-10 18:26 |
| #4 According to Dr R. Chindambaram (who has actually tested a series of nuke weapons).. the strength of the seismic signal is determined by the way the explosive energy couples into the geological medium, and there are strong regional differences. In fact, each seismic station has to be calibrated, and this is obvious from the range of seismic magnitudes reported by various global seismic stations. A small difference in body wave magnitude of a little over 0.2 corresponds to a halving of the yield estimate. And for any underground nuclear explosion, seismic body wave magnitudes are known to range over 1.0 or even more, which indicates the pitfalls in yield estimates from seismic signals, unless they are done carefully and correctly. |
| Posted by: john 2006-10-10 18:20 |
| #3 john I am at a loss for words after that |
| Posted by: sinse 2006-10-10 18:18 |
| #2 That's my understanding as well, John. And that means that seismic data alone do not tell us much, including whether this was a small nuclear blast, a failed blast or (improbable but not ruled out by the public data I've seen so far) a deliberately deceptive conventional blast. |
| Posted by: lotp 2006-10-10 18:10 |
| #1 Seismologists are using equations of the form Mb = a + b log(Yield in kT) For the Nevada test site Mb = 3.92 + 0.81 log Y These attenuation coefficients come from testing known yield weapons (yield known from previous atmiospheric test) at the test range. They depend on the rock found at the test site. For the Kazakstan site Mb = 4.45 + 0.75 log Y The US detonated an 80 kiloton nuclear device in the Aleutian Islands to simulate the geological conditions of the Soviet test site. Using the formula above, the measured seismic magnitude of 5.9 would correspond to a yield of 85 kilotons, in good agreement with LongshotÂ’s known yield of 80 kilotons. Now, it appears they are using Mb = 4.262 + 0.973 Log Y Without any knowledge of the NoKo geology or having any calibration test. They are pulling these coefficients out of thin air. This is shoddy science. Change the coefficients slighly and you suddenly get 10 kT yield, rather than 0.5kT. Add the fact that NoKo used an old mine, where a huge cavity would be available. (in the 1970s) Albert Latter, of the RAND Corporation, presented preliminary findings on the principle of cavity decoupling --- the explosion of a bomb in an underground cavity large enough that the surrounding rock would not deform plastically (permanently) in any direction, but remain elastic. Under such conditions, according to Latter, the seismic signal could be reduced by a factor of as much as 300, thereby rendering impossible the detection of all but the very largest tests None of these "experts" have a clue about the real yield of the test. All talk of "fizzle" is just speculation |
| Posted by: john 2006-10-10 17:50 |