From a data set of 150 digital records of T phases from 71 sources obtained
on seismometers of the Polynesian Seismic Network, we define a discriminan
t separating earthquake and explosion sources, which uses the maximum ampli
tude of recorded ground velocity, measured on its envelope, e(Max) (in mum/
s), and the duration of the phase measured at 1/3 of maximum amplitude, tau
(1/3) (in seconds). Earthquake sources and man-made explosions are effecti
vely separated in a log-log space by the straight line.