SEISMIC ANOMALIES IN THE AFTERSHOCK SEQUENCE OF NOVEMBER 16, 200 IN PAPUA NEW GUINEA

The study of seismic anomalies, related both to the temporal trend of aftershock sequences and to the temporal series of mainshocks, is important for an understanding of the physical processes relating to the existence and the characteristics of seismic precursors. The purpose of this work is to highlight some methodological aspects related to the observation of possible anomalies in the temporal decay of an aftershock sequence. It is realized by means of several parameters. We focused our work on an analysis of the Papua New Guinea seismic sequence that occurred on November 16, 2000. The magnitude of the mainshock is M = 8.2. The observed temporal series of shocks per day can be considered as a sum of a deterministic contribution and a stochastic contribution. If the decay can be modeled as a nonstationary Poisson process where the intensity function is equal to n(t) =( K(t + c)^–p) + K1, the number of aftershocks in a small time interval delta(t) is the mean value n(t)*delta(t), with a standard deviation sigma=( nt(t) delta(t))1/2 . We observe that there are some variations in seismicity that can be considered as seismic anomalies before the occurrence of a large aftershock. The data, checked according to completeness criteria, come from the website of the USGS NEIC data bank (http://neic.usgs.gov/neis/epic/).