Using the US Geological Survey to track earthquakes, I found 3 epicentres of close proximity of one another within 7 years. This was in a small area inside North Korea. I would not assume this to be an earthquake of any kind. But rather, something completely artificial. So with the data included below this post, I presumed that this could only be the result of several systematic underground nuclear tests. But I will only focus on the largest and most recent nuclear explosion.
Epicentre 1 (M5.1) /Centre (blue)
Date/Time: 2013/02/12 (03:57:51 UTC+01:00)
Location: 41.308°N 129.076°E (uncertainty: ± 11.2 km)
Depth: 0.0km (uncertainty: ± 1.8 km)
Minimum distance: 370.3 km (3.33°)
Event ID: usc000f5t0
DYFI = VI (11 responses in 8 cities)
Below shows a fairly standard Distance/Intensity plot where a moderate negative correlation is drawn. But intensity appears to tapers off at around 80km and declines at a slower rate.
And, the responses (for the DYFI report) vs Time. The first report came approximately half-way between 30min and 60min.
And just for fun… Theoretical P-Wave travel times map for the world. Here is the table for this data in HTML format. As you can see, it takes little under 12 minutes for the p-wave to reach London from the epicenter.
Here’s a statement from the US to the UN regarding this (and previous tests):
Finally, here’s the data for the other epicentres.
Epicentre 2 (M4.7) /Left
Date/Time: 2009/05/25 (01:54:43 UTC+01:00)
Location: 41.303°N 129.037°E (North Korea)
Epicentre 3 (M4.3) /Right
Date/Time: 2006/10/09 (02:35:28 UTC+01:00)
Location: 41.294°N 129.094°E (North Korea)