Scientists examine seismic data from North Korean nuclear test

North Korea's unconfirmed nuclear test on 9 October displayed several characteristics not typical of earthquakes that indicate it was indeed a nuclear test, according to Paul Richards, a seismologist with the Lamont‐Doherty Earth Observatory of Columbia University, Palisades, N.Y. Richards said these characteristics include a type of seismic surface wave indicating the event occurred at shallow depth (less than one or two kilometers) and thus likely of anthropogenic origin; impulsive quality of the waves at the beginning of the seismogram; and very weak shear waves.