North Korea nuclear test - seismic verification

Science & Technology Review, a publication of Lawrence Livermore Labs, coincidentally has an article on seismic verification of nuclear testing in its latest edition, although not late enough to mention the latest nuclear test of North Korea.

I'm too lazy to paraphrase an article already well written. It starts out as follows:

AN earthquake, a nuclear test, and a mine collapse all cause seismic disturbances that are recorded at monitoring stations around the world. However, these three types of events produce very different ground motions at their source. Earthquakes are caused by sideways slippage on a fault plane, while underground nuclear explosions push outward in all directions. A mine collapse is a massive vertical roof fall.

Lawrence Livermore is at the forefront of research to more accurately distinguish nuclear explosions from the rest of Earth’s never-ending seismic activity, including earthquakes large and small, volcanoes, and waves crashing on shore. The Laboratory’s work was unexpectedly put to the test following the August 2007 collapse of the Crandall Canyon coal mine in Utah, which killed six miners. Ten days later, another collapse killed three rescue workers. Both events were recorded on the local network of seismic stations operated by the U.S. Geological Survey (USGS) as well as on the USArray stations, which are part of EarthScope, a program funded by the National Science Foundation. There was considerable contention about whether the initial magnitude-3.9 event was caused by an earthquake or a collapse.

At the time, Livermore seismologists were working with colleagues from the University of California at Berkeley on a waveform-matching technique to distinguish among nuclear explosions, earthquakes, and collapse events. This technique compares seismograms produced by computer modeling with recorded data at local to regional distances (from 0 to 1,500 kilometers) for periods of 5 to 50 seconds. Livermore’s analysis of the August 2007 seismograms pointed to a collapse rather than an earthquake. The important result for the Laboratory team was being able to identify the Crandall Canyon event from its seismic signature despite its small magnitude.

Livermore’s seismological research is part of the Department of Energy’s support for the U.S. National Data Center in the area of nuclear treaty verification. (See the box below.) The team’s experience with the Crandall Canyon Mine has given the Livermore seismologists even greater confidence that they can identify a relatively small nuclear test using the same technique.

More to come on this. Or go to the link, and read the whole article now.