Monday, October 09, 2006

 

North Korea nuclear test

The North Koreans conducted an underground detonation of a nuclear bomb today.

These are the seismograms of the nuclear test in North Korea (data from the IRIS website.

The first shows the raw data:



This image shows the same data with a regional filter applied (1-10 Hz). I don't know the rationale for applying this filter, but it looks like that's the way IRIS displays their data (can you tell I'm not a seismologist?).



For comparison here are the records from the same stations for a M5.9 event at a depth of 359.5 km in the Sea of Japan (both stations were further from this earthquake than they were from the North Korean test).

This is a plot without a filter.



This is a plot with a filter.



Here's another earthquake for comparison. This one is a M 5.5 event at a depth of 71.6 km that occured near Kyushu.

No filter.



Filter.



I'm not sure how to distinguish between a nuclear blast and an earthquake. To my untrained eye it looks like the North Korean event is more impulsive (for lack of a better word) than the Sea of Japan event. However the North Korea event looks similar to the Kyushu event to me (of course the Kyushu event is much closer in depth to the North Korea event too). I see some differences in the later arrivals, but I don't know if I'm just seeing things.

UPDATES

I forgot to link to the post at No Se Nada that prompted me to look for the seismograms for the North Korean test.

Highly Allochthonous (great name) also has a post.

UPDATE: Posts at WG about the North Korea nuclear test:

Radioactive material detected from North Korea

Guestblog: Teachable Moment: North Korea nuclear test

More recordings of nuclear blasts

North Korea nuclear test

Comments:
Thanks for digging them out - I hope you don't mind, but I've borrowed them!

The larger amount of seismic energy received as early arriving P waves, compared to later arriving S waves, is what marks this out as a probable explosion.
 
Hi cjr,

You're welcome to them (FYI I generated them using Wilber II). I suppose I should have mentioned that in the original post.

Thanks for the information too, that makes sense.
 
Thanks for the link - I'll just note that due to correction of a rather embarassing spelling error, the address of my post is now this
 
I didn't notice any error (but then again I make a fair number of them myself). Thanks for the new link - I've updated my update.
 
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