Seismic Monitoring of North Korea Nuclear Tests

Alan Kafka
Weston Observatory
Department of Earth and Environmental Sciences
Boston College

People have been asking why Weston Observatory didn’t record the recent “seismic event” in North Korea.

It was much too small (magnitude 5.1) for us to see it this far away at our New England Seismic Network (or BC-ESP) stations. For us to see a seismic event at that distance, it would probably have to be about a magnitude 6.0 or higher. However, Weston Observatory seismologists also track recordings at seismic stations operated by collaborating observatories that are closer to North Korea.

Here are the seismograms at Weston, MA where it wasn’t recorded and at the IRIS/USGS station at Mudanjiang, China (MDJ) where it was recorded very well. This figure shows the MDJ seismogram and also the “spectrogram” (multi-colored plot, calculated by Dr. Jay Pulli, Visiting Scholar at Weston Observatory).

(Click to enlarge.)

 ______________

In this next figure (from IRIS and USGS) you can see the 1/6/2016 event seismogram, superposed on three other seismograms of previous North Korea nuclear tests. The seismograms are so similar that it is hard to distinguish the 2016 event (shown in red). This was one of the first clues that the event was probably a North Korea nuclear test. The biggest difference is just the relative sizes of the nuclear tests.

(Click to enlarge.)

 ______________

​Seismologists will be studying these, and other, seismograms of North Korea nuclear tests for forensic analysis of details of the nature of the 1/6/2016 event.