First question would be location in regards to the suspected site where Japan believes a test is soon to occur. Unfortunately I'm not feeling well enough yet to try to figure the geography out. If this is in the area, then the second question needs to be asked, why so many explosions, as indicated in the article. If not mining, or demolition then possible calibration testing. If it is in the area where it is suspected that a test (when it happens) will take place, then I'd lean towards calibration testing.
http://au.news.yahoo.com/060827/3/10ayb.html
Monday August 28, 09:12 AM
N. Korea Says It Conducted Large-Scale Blast Op For Waterway
SEOUL, Aug 28 Asia Pulse - North Korea said Sunday it conducted a large-scale blast operation two days ago for a waterway project.
The operation was carried out on Friday in a reservoir at Goksan county of Hwanghae province near the border with the South's Gangwon province, the North's Korean Central Broadcasting Station reported.
"The large-scale blast operation paves the way for the completion of the Risang Reservoir Project earlier than scheduled," the broadcaster said.
On Aug. 18, U.S.-based ABC News, citing unidentified U.S. officials, reported North Korea may be preparing to conduct its first underground nuclear test.
Immediately after the report, however, South Korean Unification Minister Lee Jong-seok told lawmakers on Aug. 19 he hadn't heard of any new evidence that North Korea is making such preparations.
(Yonhap)