3.8 on Richter scale = 1kt

Under normal circumstances, a yield of 1 kiloton (kt) creates seismic waves approximately equal to a magnitude 4.0 earthquake. (A kiloton is defined as 1012 calories of energy. The first U.S. nuclear detonation, the Trinity test, had a yield of 21 kt.) A country can, however, attempt to weaken the waves by conducting the test in a large underground chamber. Called decoupling, this difficult procedure could reduce the vibrations of a 1 kt test to the equivalent of a magnitude 2.5 quake.

According to Bratt, the completed seismic network will detect quakes and blasts of magnitude 4.0 or greater with a high degree of confidence, meaning that 90 percent of these events will trip at least three sensors. The system will also have the ability to pinpoint detections to a fairly small area, 1,000 square kilometers. This corresponds to a circle with a radius of 18 km. Though 1 kt represents the nominal threshold, the monitoring system is designed to catch many smaller blasts as well. "Even at 300 tons, which is pretty small, we still have, say, a 50 percent probability of detecting it," says Bratt. Any potential evader must therefore weigh the odds of getting caught even when testing at low yields.

http://www.sciencenews.org/pages/sn_arch/5_11_96/bob1.htm

this is much lower than the Trinity blast that gave around 20kt

it's not impossible to pile up 1000 tons of TNT in a tunnel. Specially for a country like North Korea where this kind of endeavours can be done to any price, with forced labour etc...

I think there could be other methods to detect for example a gamma ray burst from a satellite or a spy plane or drone. Timing is difficult though.

opaque to anything gamma - I would not be suprised if little or no gamma would be expected.

There are some intensity effects, so it is possible, but I would not bet on it.

but I don't know if the technology is already in use

http://www.llnl.gov/str/May06/Fabris.html

can they send into space? (in terms of mass)

First, fission devices don't make a lot of gamma rays, their primary spectrum is in the X-ray, somewhat softer than gamma. One would therefore expect a burst of X-rays, not of gamma rays.

Second, correct, they would pretty much all be absorbed by the ground; it is very unlikely that any of them would make it to the surface. They are penetrating radiation, but not as penetrating as gamma rays are.

Third, the detector could be put on a satellite to be deployed by the shuttle on one of those classified Air Force missions. For that matter, if you can fit it in a truck or on a buoy in a shipping lane, then you can probably put it on a rocket without a lot more fuss than, say, a Keyhole or RORSAT.

Now, given a device of this type, the fission products would likely emit gamma; and it is likely this could be detected, in a surface detonation. And the specific frequencies of gamma identify the source; radioactive decays give off gamma spectra that are unique, and spectroscopy can be used to identify the source. But I'm not so sure that a low-power source of gamma would be easily detectable from orbit, because of the fall-off by the inverse square law. I'd think anything detectable from orbit would need to be a relatively powerful source, though not outrageously so. So it's entirely possible that a nuclear weapon could be detonated underground and not be detected by such a device for some time afterward, until the radioactive material had time to make it to the surface, and perhaps never.

I see no conclusive, objective evidence either way at this time.

If they set it off underground -- and the USGS is reporting a depth of 9.3 miles on this event -- then the 4.2 seismic reading might not be accurate. This may have been larger than it looks.

I'm sure Kim will let us know how big a bomb it was. :scared:

but 15 km sounds very deep for a vertical tunnel.

Bad conclusions alert. :)

The depth is 0, and I was reading the wrong line earlier in my haste.

Significantly larger...

Equivalent to the Hiroshima bomb.

that has to be pretty close to 1 Hiroshima...

Which, is about what you would expect from NK...

Oh, wait a minute they did work. We were just lied to and told they didn't work by our media until other countries pointed out that our media and government were lying to us.

Need to figure in the "protect Bush at all costs" factor into any of these reports from our media or government.

Don

before the North Koreans start nuking Los Angeles, and it is too late!

:sarcasm:

isn't that about as much as a hamburger with french fries?
^_^

I think when you have to be on rigorous diet you're told not to exceed 1000 cal...
Or do i miss something here?




Oh, plus 1 cal for that diet coke!
^_^

Pretty sure the author meant 10¹² calories.

In other words, squite a few Big Macs even with the supersized fries...

Tesha

http://www.ktvu.com/news/10030088/detail.html

Russia: N. Korea Nuke Test Similar To Hiroshima

POSTED: 7:55 pm PDT October 8, 2006
UPDATED: 5:22 am PDT October 9, 2006

SEOUL, South Korea -- North Korea said it has successfully tested a nuclear weapon underground but there are conflicting reports on the size of the blast.

Russia's defense minister said the test was the equivalent of 5,000 to 15,000 tons of TNT. That's along the lines of the Hiroshima bomb in World War II -- and much larger than the force given earlier by South Korea's geological institute. It said the explosion was equivalent to 550 tons of TNT.

In 1996, France detonated a bomb southeast of Tahiti that had a yield of about 120,000 tons of TNT.

One U.S. official said the North Korean test was "more fizzle than pop."