This is the site of the North Korean underground nuclear test on May 25, 2009.
The state says it was more powerful than the previous one in October 2006.
A number of external agencies have confirmed a powerful explosion took place, suspected to be associated with a nuclear test.
http://search.us.reuters.com/query/?q=North%20Korea%20nuclear%20test&s=US&searchWhere=NEWS
http://earthquake.usgs.gov/eqcenter/recenteqsww/Quakes/us2009hbaf.php