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Abstract: The aim of our search is the analysis of aftershock temporal series following a mainshock with magnitude M ≥7.0. Investigating aftershock behavior may find the key to explain better the mechanism of seismicity as a whole. In particular, the purpose of this work is to highlight some methodological aspects related to the observation of possible anomalies in the temporal decay. The data concerning the temporal series, checked according to completeness criteria, come from the NEIC-USGS data bank. Here we carefully analyze the New Guinea 29 April 1996 seismic sequence. The observed temporal series of the shocks per day can be considered as a sum of a deterministic contribution (the aftershock decay power law, n(t)= K·(t + c)−p + K 1) and of a stochastic contribution (the random fluctuations around a mean value represented by the above mentioned power law). If the decay can be modeled as a non-stationary Poissonian process where the intensity function is equal to n(t)= K·(t + c)−p + K 1, the number of aftershocks in a small time interval Δt is the mean value n(t)·Δt, with a standard deviation . [Copyright &y& Elsevier]