IN the NPR news item North Korea Possibly Conducts Sixth Nuclear Test, South Korea Says:
The U.S. Geological Survey says it detected a 6.3 magnitude "possible explosion" near Sungjibaegam, North Korea Sunday afternoon, "located near the site where North Korea has detonated nuclear explosions in the past."
South Korean Joint Chiefs of Staff say they detected an "artificial seismic wave" at 12:29 p.m. local time and are "currently looking into the possibility of it being a nuclear test."
The incident was near North Korea's Punggye-ri nuclear test site, which is in the country's northeast and the site of the five previous tests.
The magnitude and location of the event are strongly suggestive of the cause, but if the location were very different, it sounds like the nature of the seismic waves would already indicate that the source was artificial rather than a natural geological seismic event.
Question: What is it about a seismic wave measurements that would allow one to distinguish between natural geological and artificial causes?
below: "North Korea has conducted six nuclear tests. As this chart of seismic activity shows, the latest test on Sept. 3 was roughly an order of magnitude larger than earlier ones." From the NPR new item Here's How Big North Korea's Latest Nuclear Test Actually Was, Original: CTBTO