The Partitioning of Radiated Energy and the Largest Aftershock of Seismic Sequences Occurred in the Northeastern Italy and Western Slovenia

We analyzed the most relevant seismic sequences occurred from 1977 to 2007 in the FriuliVenezia Giulia region (northeastern Italy) and western Slovenia. The 8 aftershock sequences were triggered by low to moderate magnitude earthquakes with mainshock duration magnitude ranging from 3.7 to 5.6. The b-value of the Gutenberg-Richter law varies from 0.8 to 1.1. The modified Omori’s modeling of the sequences evidences values of the p exponent ranging from 0.8 to 1.0. Using the Reasenberg and Jones (1989, 1994) approach, we computed the probabilistic estimate of the aftershock rates and the largest aftershock in given time intervals. The difference in magnitude between the mainshock and the largest aftershock is calculated according to the modified Båth law and using an approach that considers the partitioning of the radiated seismic energy between mainshock and aftershocks. The partitioning of the radiated seismic energy appears to play a significant role in the evolution of the sequences. We define the parameter RES as the ratio between the radiated seismic energy of the mainshock and the summation of the seismic energy radiated by the aftershocks. The difference in magnitude between the mainshock and the largest aftershock, calculated with the parameter RES, agrees well with the observed difference. In most sequences, the parameter RES decreases very quickly till the occurrence of the largest aftershock and then becomes constant. By analyzing the values of RES during the early hours following the mainshock, we found that the RES values after 24 hours are well related to the final ones, calculated on the whole sequence, and to the differences in magnitude between the mainshock and the largest aftershock. ha l-0 06 46 23 2, v er si on 1 29 N ov 2 01 1 Author manuscript, published in "J Seismol (2008)" DOI : 10.1007/s10950-007-9075-x