While an average of 20,000 quakes above magnitude 4.0 are reported
annually, seismologists figure that at magnitude 2.5, that number is 120,000-a
formidable string of ambiguous rumblings to sift through. In addition, another
hundred thousand chemical explosions are set off by mining operations. While
these are often less than magnitude 3.0, determined testers can hide nuclear
explosions by synchronizing the blasts.
Researchers Scott Phillips and Craig Pearson of the Los Alamos National
Laboratories are compiling more detail of the seismic signatures of all
possible events into a library. They hope to profile a unique "nuclear
fingerprint" for even very small explosions. Similar work with underwater
blasts is also underway.