Earthquake sensors picked it up as a 4.5.
"A reading of 4.0 and 4.2 on the Richter scale would corresponding to a nuclear explosive yield of about 0.5 and 0.9 kt of TNT-equivalent, respectively, according to the above equation. Thus, the most easily obtained estimate of the size of the explosion is 0.5-0.9 kt. This is a yield given for small tactical nuclear warheads formerly in the American arsenal; and is a small fraction of the yield of first tests of other countries (19 kt US, 25 FSU, 25 UK, 60 France, 22 China, 12 India, ~9 Pakistan)."
http://www.nautilus.org/fora/security/0689HayesKang.html